Re: [MBZ] DIY AC repair in modern times
It's not the flamability that is the problem, they all ignite about the way, but a slowly evaporating liquid and a substance that is a gas a atmospheric temperature and pressure are very different in explosion hazard. Halogenated hydrocarbons (all Freons, and anthing else with at least one chlorine or fluorine or bromine atom added) are NOT flammable under normal conditions, although most of them can be induced to burn. They don't explode as dilute mixtures in air, and that is the cogent point here, not flammability. Propane powered vehicles do NOT have high pressure propane in the tank, it's cool to cold and liquid at fairly low pressure. An AC system on a hot day will have hot gas (250F or so, maybe higher) in the condenser, it doesn't become a liquid until it's cooled. All propane tanks have anti-venting valves, so that tearing the regulator off (or uscrewing it with the tank valve open) will cause the tank to seal off. The fuel lines up to the engine have about the same pressure as the one to the burner valves on a gas grill. Peter
Re: [MBZ] DIY AC repair in modern times
The green ones are a different material, just what I don't know. The older black 0-rings don't last well in PAG or PEG compressor oil, although they will last nearly forever in mineral oil. All McParts stores have them, and I'm sure Rusty does. He will have the correct ones, makes it easier to get the correct ones in place -- the kits at McParts have dozens of sizes, and never enough of just the one you need -- there are at least six different ones I've found so far! Peter
Re: [MBZ] DIY AC repair in modern times
It gets hot a steamy here, but probably 1 degrees cooler than Dallas. You will probably be short of cooling in idling or slow traffic unless you get a larger condenser, I don't know of any way around that. Mine work fine -- I've never been comfortable in any car idling it traffic with the AC on anyway, so I don't notice it much. Once you get moving I cannot tell the difference. I would suggest replacing the condenser if it has a lot of miles on it, they collect crud internally over the years that reduces cooling. You must also have the system completely dry -- 134a makes hydrofluoric acid in the presence of water and heat. Peter
Re: [MBZ] DIY AC repair in modern times
On Jun 13, 2006, at 3:10 PM, Mitch Haley wrote: The gas dealers always have come pictures on the wall of cars which had leaky acetylene tanks in the trunk, most impressive. A garbage bag full of the stuff can take a the windows out of a few houses. I once drove home from Chicago with a couple pair of tanks in the passenger compartment with me (never in the trunk). If I'd smelled anything like almonds, I would have pulled over, left the door open, and run like heck. I knew a young guy who worked for his father's scrap/roll-off dumpster business. He had oxygen and acetylene bottles in the cab of his Mack heading into manhattan on the Williamsburgh Bridge. Anyone who is familiar with driving on this bridge knows that there is a jog in the roadway where some of the structure must be driven around. This kid hit the structural steel and a few other large immovable objects and the tanks exploded. The driver was tall and obese, small parts of him were found in the wreckage but nothing anyone would recognize as being Dave Jr. or part of any human, for that matter. I have transported tanks several times in an unsafe manner but never again after that wake-up call. Johnny B. I Mac Therefore I am
Re: [MBZ] DIY AC repair in modern times
Once you get moving I cannot tell the difference. I would suggest replacing the condenser if it has a lot of miles on it, they collect crud internally over the years that reduces cooling. You must also have the system completely dry -- 134a makes hydrofluoric acid in the presence of water and heat. Peter Well I've decided to replace the compressor, manifold line and the dryer. I will reuse the switches on the dryer, and if it looks clean inside I am going to try to have it evacuated / recharged with R12 It is currently R12. Rusty's site has 2 kinds of o-rings listed, one of them tools like what I call an o-ring the other looks wore like a flat 'rubber' washer. They are both listed for use with the R4 compressor the difference being 'stepped ports?'. What up with this? George Larribeau Dallas, Texas 1985 300SD 190K
Re: [MBZ] DIY AC repair in modern times
Rusty's site has 2 kinds of o-rings listed, one of them tools like what I call an o-ring the other looks wore like a flat 'rubber' washer. They are both listed for use with the R4 compressor the difference being 'stepped ports?'. What up with this? My guess is that they changed the way the manifold attaches at some point, and it may be the only way to know which style you need is to look. Perhaps you just have to order both sets and eat the wrong ones? Be silly to return something that small I'd think. -- Jim
Re: [MBZ] DIY AC repair in modern times
My guess is that they changed the way the manifold attaches at some point, and it may be the only way to know which style you need is to look. Perhaps you just have to order both sets and eat the wrong ones? Be silly to return something that small I'd think. -- Jim Buying extra o-rings is no big gig. However not knowing for a fact what the right ones are is another matter. Hopefully it will become obvious upon receipt of the parts. It would be a bummer to believe it was working and have it fail later .. George Larribeau Dallas, Texas 1985 300SD 190K
Re: [MBZ] DIY AC repair in modern times
Peter Frederick wrote: Propane is a compressed gas in an AC system, and hot while in use. Gasoline is a liquid, and while it will readily ignite and burn, it is NOT explosive unless atomized or very hot (yes, a gas tank IN A FIRE will explode, but liquid gasoline just spilled will not). Gasoline is a liquid, but a very volatile one. Just about any amount of liquid gasoline will form a flammable mixture in the air around it. I've heard it said that if you can smell gasoline, you're probably standing in a flammable atmosphere. Propane, by contrast, needs to reach a fairly narrow range of mixtures in the air before it will burn. Just look at how finicky it is to light some propane burners! As I said before, if there is air INSIDE the AC system, you can easily get high enough temps to ignite it, with shrapnel from the detonating compressor blown around. Do you have any references to this actually happening? I'm not saying it's impossible, but the chances seem really remote. If it's really as dangerous as you say, though, there ought to be some stories in the news. The issue is strictly safety -- hydrocarbons work pretty well as refrigerants. Its the flamability and explosion hazard that makes them unsafe. I suppose all the cars that are actually *running* on propane must be hideously unsafe too, then? I mean, they're carrying a high pressure tank with 20 gallons of the stuff, plus lines of it at 30 psi in the hot engine bay...
Re: [MBZ] DIY AC repair in modern times
Have you ever punctured a propane tank? Not like a rubber hose or aluminum condenser. Propane is explosive over exactly the same range as gasoline vapor, they are both hydrocarbons. I won't go into the difference between a volatile liquid like gasoline that takes an hour os more to evaporate a pint and the equivalent amount of propane that will make an explosive mixture on contact with air as it expands instantly when released. Gasoline isn't all that safe, either, witness the occasional severe burns received when a spark ignites the vapors while someone is filling something, usually a fuel can. Note that there is almost never an explosion, just a fire. With a propane filled AC system, a collision that puntures the condenser will provide a spark or many as the propane vents and everything folds up -- the resulting blast will probably blow the fenders off. A leaking tank in the car will roast the paint right off -- do a web search, not funny. You should NEVER carry propane tanks in a closed car!. Propane fueled vehicles have armored piping and flow restrictors in the pipes to prevent just such an explosion (notably pressure regulators that reduce the line pressure to 1 or 2 psi, not 300 psi), not something you can install in an AC system. Peter
Re: [MBZ] DIY AC repair in modern times
Propane is explosive over exactly the same range as gasoline vapor, That is not true. Anyone with any experience with propane torches or BBQ grilles knows that propane is finicky about its mixture with air if it is to combust. I have _never_ heard of anybody having any difficulty in lighting a gasoline fire! they are both hydrocarbons. That is true. -- Jim
Re: [MBZ] DIY AC repair in modern times
Well the hydrocarbons are legal in about every other country David Brodbeck wrote: Peter Frederick wrote: The propane is vastly more explosive than the oil -- this is, in fact, why hydrocarbon refrigerants are illegal in cars, not because they don't work well (very low temp cryo freezers run pentane, I belive, or propane, for the low temp part), but because of the explosion hazard. On the other hand, many people put large quantities of gasoline in their cars, which forms an explosive mixture even more readily than propane. And quite a few people (myself included) have driven around in RVs with *gallons* of propane on board in exposed, external tanks, often with the tank valve open and a propane-fired refrigerator running. I'm sure there's some risk of explosion, but it's hard for me to see this as a major issue. I suspect part of the reason that hydrocarbon refrigerants are illegal is because the companies that own the patents on the non-hydrocarbon ones have a certain amount of monetary influence over the regulatory agencies. I've always thought it was a little suspicious that R12 was banned just as the patent was expiring. ___ http://www.okiebenz.com For new parts see official list sponsor: http://www.buymbparts.com/ For used parts email [EMAIL PROTECTED] To Unsubscribe or change delivery options go to: http://okiebenz.com/mailman/listinfo/mercedes_okiebenz.com -- Kaleb C. Striplin/Claremore, OK 91 300D 2.5 Turbo, 90 420SEL, 89 560SEL, 87 420SEL, 87 300SDL, 85 380SE, 85 300D, 84 190D 2.2, 83 300TD, 81 300TD, 81 240D, 76 240D, 76 300D, 74 240D, 73 280SEL 4.5, 72 250C, 69 250 http://www.striplin.net
Re: [MBZ] DIY AC repair in modern times
Kaleb C. Striplin wrote: Well the hydrocarbons are legal in about every other country I suppose they're lucky their cars haven't been going off like roman candles.
Re: [MBZ] DIY AC repair in modern times
These super bombs use a liquid fuel, not propane: http://www.fas.org/man/dod-101/sys/dumb/fae.htm The US Armed Forces use propane tanks as super bombs a small charge to dipserse the gas and an igniter charge to set it off. Turns all the people for a couple hundred yards into scattered body part. ___ http://www.okiebenz.com For new parts see official list sponsor: http://www.buymbparts.com/ For used parts email [EMAIL PROTECTED] To Unsubscribe or change delivery options go to: http://okiebenz.com/mailman/listinfo/mercedes_okiebenz.com
Re: [MBZ] DIY AC repair in modern times
What I don't get is why R-290 is so bad when gassers have been converted to LPG... and where CNG is still used in vehicles? How does the flammability of these substances compare to the flammability of gasoline? -j.
Re: [MBZ] DIY AC repair in modern times
replace all the 0-rings with new green ones when changing a system over. What is the difference between green and black o-rings. Does Rusty have them? George Larribeau Dallas, Texas
Re: [MBZ] DIY AC repair in modern times
Most undercooling problems are a result of overcharging -- R134a is lighter than R12, only put in 80 to 85% of the weight -- otherwise you get high suction side pressures and low cooling. Peter Peter, has R134 worked for you? Is the evaporator big enough? How hot is it where you live. Here in Dallas 100F+ ambient temperature is nothing. George Larribeau Dallas, Texas 1985 300SD 190K
Re: [MBZ] DIY AC repair in modern times
What is the difference between green and black o-rings. The ones formulated to also tolerate R134A are usually green. (I don't know that they'd have to be.) R134A (or its oil) attacks the black rubber ones that were good for R12 systems. -- Jim
Re: [MBZ] DIY AC repair in modern times
The ones formulated to also tolerate R134A are usually green. (I don't know that they'd have to be.) R134A (or its oil) attacks the black rubber ones that were good for R12 systems. -- Jim Are 'green' ones backward compatible to R12? Rusty site has 2 kinds of o-rings (with pix) Online catalogue 1985 - 00SD - Climate Control - A/C O-Ring First - A/C O-Ring - A/C Compressor - Used together with R-4 or A-6 Type A/C Compressors. (Normal round cross-section looking o-Ring) Second - A/C O-Ring - For Non-Stepped Ports - GM radial R-4 version (Flat looking rubber washer seal thing) Where else in the system are they used ? George Larribeau Dallas, Texas 1985 300SD 190K
Re: [MBZ] DIY AC repair in modern times
George Larribeau wrote: And that goes triple for any kind of acetylene gas, very serious stuff The gas dealers always have come pictures on the wall of cars which had leaky acetylene tanks in the trunk, most impressive. A garbage bag full of the stuff can take a the windows out of a few houses. I once drove home from Chicago with a couple pair of tanks in the passenger compartment with me (never in the trunk). If I'd smelled anything like almonds, I would have pulled over, left the door open, and run like heck.
Re: [MBZ] DIY AC repair in modern times
I once drove home from Chicago with a couple pair of tanks in the passenger compartment with me (never in the trunk). If I'd smelled anything like almonds, I would have pulled over... Almonds? Acetylene has a sharp acetone-y smell. It's delivered dissolved in acetone inside the tank. Now that is some flammable stuff. It can explode on its own at low pressures, like 20 psi (or some such ridiculous value) with no oxidant present, when one of the two carbon bonds lets go. -- Jim
Re: [MBZ] DIY AC repair in modern times
Are 'green' ones backward compatible to R12? I believe so. Where else in the system are they used? There are rings at all the joints in the system, anywhere it's not a flare fitting. (For example there were zero O-rings in my York-based 114 system, except for the two odd seals in the compressor fittings themselves. Everything else was a flare fitting in that car.) -- Jim
Re: [MBZ] DIY AC repair in modern times
Peter Frederick wrote: The propane is vastly more explosive than the oil -- this is, in fact, why hydrocarbon refrigerants are illegal in cars, not because they don't work well (very low temp cryo freezers run pentane, I belive, or propane, for the low temp part), but because of the explosion hazard. On the other hand, many people put large quantities of gasoline in their cars, which forms an explosive mixture even more readily than propane. And quite a few people (myself included) have driven around in RVs with *gallons* of propane on board in exposed, external tanks, often with the tank valve open and a propane-fired refrigerator running. I'm sure there's some risk of explosion, but it's hard for me to see this as a major issue. I suspect part of the reason that hydrocarbon refrigerants are illegal is because the companies that own the patents on the non-hydrocarbon ones have a certain amount of monetary influence over the regulatory agencies. I've always thought it was a little suspicious that R12 was banned just as the patent was expiring.
Re: [MBZ] DIY AC repair in modern times
Kaleb Striplin suggested an electronic leak detector. The cheapest one I found, Toolsource.com, was about $175. I'll keep that in mind if cheaper methods don't work. I have one I bought at a pawn shop for considerably less. I also have another one (same source) that detects hydrocarbons. The pair of them was less than the above figure. -- Jim
Re: [MBZ] DIY AC repair in modern times
Hadn't thought of that source. I'll check the pawnshops. Thanks, Gerry - Original Message - From: Jim Cathey [EMAIL PROTECTED] To: Mercedes Discussion List Mercedes@okiebenz.com Sent: Monday, June 12, 2006 9:00 AM Subject: Re: [MBZ] DIY AC repair in modern times Kaleb Striplin suggested an electronic leak detector. The cheapest one I found, Toolsource.com, was about $175. I'll keep that in mind if cheaper methods don't work. I have one I bought at a pawn shop for considerably less. I also have another one (same source) that detects hydrocarbons. The pair of them was less than the above figure. -- Jim
Re: [MBZ] DIY AC repair in modern times
Propane is a compressed gas in an AC system, and hot while in use. Gasoline is a liquid, and while it will readily ignite and burn, it is NOT explosive unless atomized or very hot (yes, a gas tank IN A FIRE will explode, but liquid gasoline just spilled will not). The US Armed Forces use propane tanks as super bombs a small charge to dipserse the gas and an igniter charge to set it off. Turns all the people for a couple hundred yards into scattered body part. As I said before, if there is air INSIDE the AC system, you can easily get high enough temps to ignite it, with shrapnel from the detonating compressor blown around. The issue is strictly safety -- hydrocarbons work pretty well as refrigerants. Its the flamability and explosion hazard that makes them unsafe. All the halogenated hydrocarbon refrigerants are fire suppresors (the halogen atoms absorb electrons and poison the combustion) -- in fact, Halon is one of them. Peter
Re: [MBZ] DIY AC repair in modern times
electronic leak detector archer wrote: If you convert to 134-A can you then go back to R-12 using your 134-A set of gauges? R-134-A doesn't do a very good job of cooling my MBs. I'm currently trying to find a second leak in an '83 300D. The first one was the pressure switch on top of the dryer which is now fixed. I'm using UV dye to look for the leaks, and I've wasted four cans of Freon trying to find it under the hood. Can someone tell me the best way to find it under the dash since that must be where it is? Thanks, Gerry Archer '83 300D and 240D - Original Message - From: Peter Frederick [EMAIL PROTECTED] To: Mercedes Discussion List Mercedes@okiebenz.com Sent: Saturday, June 10, 2006 3:36 PM Subject: Re: [MBZ] DIY AC repair in modern times Isobutane/propane refrigerant will work very nicely. However, if you have a leak, air leaks in while the hydrocarbons leak out, and you can get an explosive mixture fairly easily. The result can be a detonating compressor (don't laugh, I've seen it). You also risk a large explosion if you have an accident that punctures the condenser. You must indeed charge by pressure, adding 2.2 lbs of propane will definitely burst something. When whatever it is ruptures, you can get a propane/air explosion. R134a isn't much more expensive, is inert, and conversion isn't that hard. Peter ___ http://www.okiebenz.com For new parts see official list sponsor: http://www.buymbparts.com/ For used parts email [EMAIL PROTECTED] To Unsubscribe or change delivery options go to: http://okiebenz.com/mailman/listinfo/mercedes_okiebenz.com -- No virus found in this incoming message. Checked by AVG Free Edition. Version: 7.1.394 / Virus Database: 268.8.3/360 - Release Date: 6/9/2006 ___ http://www.okiebenz.com For new parts see official list sponsor: http://www.buymbparts.com/ For used parts email [EMAIL PROTECTED] To Unsubscribe or change delivery options go to: http://okiebenz.com/mailman/listinfo/mercedes_okiebenz.com -- Kaleb C. Striplin/Claremore, OK 91 300D 2.5 Turbo, 90 420SEL, 89 560SEL, 87 420SEL, 87 300SDL, 85 380SE, 85 300D, 84 190D 2.2, 83 300TD, 81 300TD, 81 240D, 76 240D, 76 300D, 74 240D, 73 280SEL 4.5, 72 250C, 69 250 http://www.striplin.net
Re: [MBZ] DIY AC repair in modern times
Ah, but in fact air will diffuse through a small leak against a pressure gradient -- something I have trouble convincing the technicians at work of as well. If the evaporator is very cold due to low charge, you can and will get below atmospheric pressures occasionally as well, and a big leak will allow considerable mixing of air into the propane. The propane is vastly more explosive than the oil -- this is, in fact, why hydrocarbon refrigerants are illegal in cars, not because they don't work well (very low temp cryo freezers run pentane, I belive, or propane, for the low temp part), but because of the explosion hazard. There should be about 4 oz of oil compared to a pound or so of volatile propane. Only the oil mist is explosive, but the entire charge of propane is, and the oil; mist will drop out of explosive mixture range very quickly, while the propane has to be diluted out with air. Use at your own risk. Propane will leak out about the same rate as R134a -- with good hoses and new o-rings, I wouldn't expect to charge every year. You still have a leak, likely a compressor shaft seal (look for oil behind the drive pulley) or in the manifold or hoses. If it won't hold a vacuum overnight, it's leaking! A small nick in an o-ring will dissipate a charge over the summer and be fairly hard to find -- as I've learned on the TE. Peter
Re: [MBZ] DIY AC repair in modern times
The high side o-rings on the pump to manifold seal, right? These are known to erode with age -- the heat and pressure are highest here. They died on the TE before I converted, but only failed big time afterwards. I redid the body seals and found when I took the manifold off that I probably didn't need to -- after I took the front cover off. This is a normal failure, not related to use of R134a. The new o-rings intended for R134a are the same as the old ones. They did look much like rats had been chewing on them. Ditto for the manifold to hose set seals -- had to replace those o the 300D, leaked out all my R12. Polyester oil will either sit on top of the mineral oil, or emulsify it and circulate it. Either way, it works fine. Most of the non-dissolved oil will end up in the pump anyway, where it is needed. PAG oil will not dissolve the mineral oil, and you should not mix mineral and PAG. If you are converting, dump all the mineral oil out of the compressor and replace with the correct amount of PAG. Peter
Re: [MBZ] DIY AC repair in modern times
I use a GowMac thermal conductivity leak detector I picked up on eBay for $35 -- they run $3500 or so new. Very sensitive, but use with caution with flamables, they use a heated platinum wire as a detection device. It actually compares the heat conducting ability of a sample of air pulled through a probe to the heat conducting ability of the environmental air. Work great except you have to watch a needle (old style, the newer ones click too) and cold, wet air gives a good signal, just the opposite of Freon! Peter
Re: [MBZ] DIY AC repair in modern times
The high side o-rings on the pump to manifold seal, right? These are known to erode with age -- the heat and pressure are highest here. I'd assume so, but I no longer remember. They looked bad, like chunks had been forcibly removed, nothing like dissolvement. This is a normal failure, not related to use of R134a. The new o-rings intended for R134a are the same as the old ones. They did look much like rats had been chewing on them. The new green ones were expensive, and in my particular case, on back-order. As I was returning to R12-ish world I went with the black ones. Polyester oil will either sit on top of the mineral oil, or emulsify it and circulate it. Either way, it works fine. Most of the non-dissolved oil will end up in the pump anyway, where it is needed. PAG oil will not dissolve the mineral oil, and you should not mix mineral and PAG. If you are converting, dump all the mineral oil out of the compressor and replace with the correct amount of PAG. I flushed my pump with gasoline to remove the PXX oil (no clue as to what it was, the conversion tag was no help), more-or-less dried it out, and put back in the specified amount of mineral oil. Time will tell whether this will hold up or not, this car is presently not being driven since we're still trying to sell the 450 SL and can't justify the expense of keeping more than one convertible on the road. -- Jim
Re: [MBZ] DIY AC repair in modern times
The gasoline should have done a fine job getting the oil out. Methylene chloride used to be the main flush solvent, don't know now. Just don't spin the pump much with no oil in it, the pistons and sleeve sets are teflon coated or some such, and no lubrication is bad for them. Might not remove PAG oil very well, though, it's more water soluble than gasoline soluble. Main thing is to get most of it out. My o-rings looked like someone had taken bites out of them. Some shreddies, too, I suppose where bits were protected by being right up against the metal. Peter
Re: [MBZ] DIY AC repair in modern times
From: archer [EMAIL PROTECTED] If you convert to 134-A can you then go back to R-12 using your 134-A set of gauges? R-134-A doesn't do a very good job of cooling my MBs. I'm currently trying to find a second leak in an '83 240D. The first one was the pressure switch on top of the dryer which is now fixed. I'm using UV dye to look for the leaks, and I've wasted four cans of Freon trying to find it under the hood. Can someone tell me the best way to find it under the dash since that must be where it is? Thanks, Gerry Archer '83 300D and 240D -- From: Peter Frederick [EMAIL PROTECTED] All the connections are sealed with o-rings, and there are four on the expansion valve. I would guess that is where your leak is, and it may be slow enough that not much oil will blow out with the freon. I replace all the 0-rings with new green ones when changing a system over. Don't forget to check the compressor, too -- the hose junction on the later models tends to leak, as does the front seal and the piping manifold to compressor body on the Nippondenso conpressors. On my TE, the leak at the manifold to body was the high side o-rings, and the oil was on the block side, invisible until I removed the compressor.\ You can go back, but you really need to flush the oil out properly. Most undercooling problems are a result of overcharging -- R134a is lighter than R12, only put in 80 to 85% of the weight -- otherwise you get high suction side pressures and low cooling. - Kaleb Striplin suggested an electronic leak detector. The cheapest one I found, Toolsource.com, was about $175. I'll keep that in mind if cheaper methods don't work. -- From: Jim Cathey [EMAIL PROTECTED] Jim, what is test refrigerant It is what I use to test a system before committing scarce and expensive R12 to it. (None of my cars has sufficiently 'passed' the test to earn my only three cans of R12.) It's a mix of isobutane and propane, and there are commercial formulations of this. Costs about $7 per full* charge DIY. * full as in fully functional, but hydrocarbon blends are usually quite undercharged when compared to an R12 installation. This is to control the pressures, since propane (R290) has an R22-like pressure curve. This makes them very sensitive to minor leakage, with the usual result being a need for an annual charge. Big deal, so I have to spend $7/year to keep AC working in each car! According to the EPA (and just how does this policy result in a protected environment?) it is not legal to use this refrigerant or anything like it in the US. The political machinations behind this policy are both frightening and disgusting, I'll leave it to you to surf for it on the web. is there a FAQ ? if you have been over and over this is it in the archives ? Only the two links I gave before: http://cathey.dogear.com/efair.html http://cathey.dogear.com/cwair.html - Thanks to Peter, Kaleb, and Jim for the information and suggestions. Bought a package of green O rings in various sizes for A/Cs yesterday, so I'll replace all you suggest while it's apart, as well as install a new dryer. Gerry Archer '83 300D and 240D
Re: [MBZ] DIY AC repair in modern times
Both pressures are low. Compressor _could_ cause this, but it sounds undercharged. I am going to put the gauges on it tomorrow. Is there a max pressure at Idle? I thought that the low side pressure was important at idle like not to exceed 28 psi or something? Am I misinformed? At what RPM should it start to work? Also I was told in an older system if you replace the compressor you should replace the expansion valve? The tale I was told on this is that here in Texas 1t 110 F with a new compressor, they will usually blow when they are old. Did I bite on some bate and swallow it hook line and sinker? What should I look for with the gauges on it tomorrow? The systems I worked on 20 years ago were 220V AC operated. Compressor output was constant. I am trying to understand when it should be working? (in terms of RPM) George Larribeau Dallas Texas 1985 300SD 170K 1987 HD FLHTC 86K 1984 Motoguzzi Cal -2 80K 1972 Motoguzzi Ambassador LOTS 1965 Chevy C-10 pick up truck lots of miles 3rd small block ..(Extra Ugly,but runs) 1993 BMW 323i 110K (Wife's Car) 1967 BMW R50/2 (Wife's MC, currently in a Basket)
Re: [MBZ] DIY AC repair in modern times
R12 low side should be above 35 psi (which, so conveniently, is also 35F) with expansion valve open (as it will be at idle). The high side pressure should be around 250 psi, higher as the external temp goes up. At 1500 rpm (the normal spec) low side pressure should be 35 and high side under 350 or so. Aux fan should run above about 250 psi, I think, although I'm not exactly sure of that. Certainly comes on as I charge my car(s). When the expansion valve closes due to low evaporator temp, the low side can drop as low as -15 psi, as it should to prevent freezeup. The compressor will also cycle on a Benz to prevent freezeup and to control cooling. Low high side pressures and no liquid in the sight glass (it looks different that the liquid, notably it will have oil bubbles) indicate a low charge. If you have intermittant very low (- 15 or lower) pressures while checking, the expansion valve is closing and the compressor is fine. Cold pressure with the compressor disengaged should be 70 to 100 psi, I think, at least significantly higher than 50 psi. I've not checked that in a long while, and you cannot charge by idle pressure (weigh the cans instead), but less than 50 psi cold with compressor disengaged would make me think low charge. If you want to stick with R12, have what is in there recovered, replace ALL the o-rings, and charge with something else to check for leaks, then repair any. You can then recharge with R12 with some assurance it will stay in. If you want to stay with R12 for the long run, I would also suggest replacing all flexible hoses with new barrier type hoses as they leak less. Peter
Re: [MBZ] DIY AC repair in modern times
When the expansion valve closes due to low evaporator temp, the low side can drop as low as -15 psi, as it should to prevent freezeup. The compressor will also cycle on a Benz to prevent freezeup and to control cooling. When charging on a hot day, as I like to do, the system ends up running flat-out and you don't usually have too much trouble with weird symptoms caused by feedback mechanisms kicking in. A big reason I like to do it then! That, and using test refrigerant instead of R12 means it's not cookbook time, you have to tinker with the (under-)charge. -- Jim
Re: [MBZ] DIY AC repair in modern times
I am going to put the gauges on it tomorrow. Is there a max pressure at Idle? I thought that the low side pressure was important at idle like not to exceed 28 psi or something? At idle it's not running very effectively, and I've found the pressures are _never_ as low as when running at speed. 28 is way too low an expectation at idle in my (limited) experience. I was told in an older system if you replace the compressor you should replace the expansion valve? Depends on why the replacement. Because expansion valves are easy to clog, if the compressor grenaded you may well have to. But if a reed valve broke and it just couldn't pump well then there would be no need, nor if it was just a bearing that went out. Did I bite on some bait and swallow it hook line and sinker? Commercial mobile AC servicing is, these days, a government-sanctioned racket IMHO. I have _never_ heard of a repair estimate that did not entail replacing at least half of the system, even if the real fault was merely a leaky O-ring. Thank you EPA. I do my own these days, and I've spent less keeping my entire fleet going, including the purchase of tools, than the _first_ estimate I had done. -- Jim
Re: [MBZ] DIY AC repair in modern times
Is there a max pressure at Idle? The modern AC system is deceptively simple. It's rather elegant engineering, which means that it's more complex than it appears. It's all about fluid dynamics, with phase changes thrown in, and a lot of weird plumbing. Testing is done by pressure gauges, thermometers, and inference, yet an important variable is the amount of fluid flow, both gaseous and liquid, for which there is no direct measurement. In electrical terms, it's like trying to diagnose a battery/starter problem using only a voltmeter and your brain. That's what most of us do and it certainly works, but it's _so_ much easier to _also_ use an ammeter to measure the current draw rather than trying to infer it. -- Jim
Re: [MBZ] DIY AC repair in modern times
The most common failures are leaks, which are fairly easy to fix, if not cheap, but a compressor failure these days almost always means changing the condenser to get rid of all the crap sitting in it -- which stuff will promptly wreck a new compressor. My friend Hans always installs a filter if he has to put a new compressor on, and they still sometimes croak from dirt. It's nearly impossible to flush the evaporators since they are multi-coil units, and the partially clogged coils won't flush. On Jun 10, 2006, at 12:07 AM, Jim Cathey wrote: Is there a max pressure at Idle? The modern AC system is deceptively simple. It's rather elegant engineering, which means that it's more complex than it appears. It's all about fluid dynamics, with phase changes thrown in, and a lot of weird plumbing. Testing is done by pressure gauges, thermometers, and inference, yet an important variable is the amount of fluid flow, both gaseous and liquid, for which there is no direct measurement. In electrical terms, it's like trying to diagnose a battery/starter problem using only a voltmeter and your brain. That's what most of us do and it certainly works, but it's _so_ much easier to _also_ use an ammeter to measure the current draw rather than trying to infer it. -- Jim ___ http://www.okiebenz.com For new parts see official list sponsor: http://www.buymbparts.com/ For used parts email [EMAIL PROTECTED] To Unsubscribe or change delivery options go to: http://okiebenz.com/mailman/listinfo/mercedes_okiebenz.com
Re: [MBZ] DIY AC repair in modern times
reason I like to do it then! That, and using test refrigerant instead of R12 means it's not cookbook time, you have to tinker with the (under-)charge. -- Jim Jim, what is test refrigerant is there a FAQ ? if you have been over and over this is it in the archives ? George Larribeau Dallas Texas 1985 300SD 170K 1987 HD FLHTC 86K 1984 Motoguzzi Cal -2 80K 1972 Motoguzzi Ambassador LOTS 1965 Chevy C-10 pick up truck lots of miles 3rd small block ..(Extra Ugly,but runs) 1993 BMW 323i 110K (Wife's Car) 1967 BMW R50/2 (Wife's MC, currently in a Basket)
Re: [MBZ] DIY AC repair in modern times
In electrical terms, it's like trying to diagnose a battery/starter problem using only a voltmeter and your brain. That's what most of us do and it certainly works, but it's _so_ much easier to _also_ use an ammeter to measure the current draw rather than trying to infer it. Thank you I am an electronics type ... GL
Re: [MBZ] DIY AC repair in modern times
Jim, what is test refrigerant It is what I use to test a system before committing scarce and expensive R12 to it. (None of my cars has sufficiently 'passed' the test to earn my only three cans of R12.) It's a mix of isobutane and propane, and there are commercial formulations of this. Costs about $7 per full* charge DIY. * full as in fully functional, but hydrocarbon blends are usually quite undercharged when compared to an R12 installation. This is to control the pressures, since propane (R290) has an R22-like pressure curve. This makes them very sensitive to minor leakage, with the usual result being a need for an annual charge. Big deal, so I have to spend $7/year to keep AC working in each car! According to the EPA (and just how does this policy result in a protected environment?) it is not legal to use this refrigerant or anything like it in the US. The political machinations behind this policy are both frightening and disgusting, I'll leave it to you to surf for it on the web. is there a FAQ ? if you have been over and over this is it in the archives ? Only the two links I gave before: http://cathey.dogear.com/efair.html http://cathey.dogear.com/cwair.html -- Jim
Re: [MBZ] DIY AC repair in modern times
Isobutane/propane refrigerant will work very nicely. However, if you have a leak, air leaks in while the hydrocarbons leak out, and you can get an explosive mixture fairly easily. The result can be a detonating compressor (don't laugh, I've seen it). You also risk a large explosion if you have an accident that punctures the condenser. You must indeed charge by pressure, adding 2.2 lbs of propane will definitely burst something. When whatever it is ruptures, you can get a propane/air explosion. R134a isn't much more expensive, is inert, and conversion isn't that hard. Peter
Re: [MBZ] DIY AC repair in modern times
If you convert to 134-A can you then go back to R-12 using your 134-A set of gauges? R-134-A doesn't do a very good job of cooling my MBs. I'm currently trying to find a second leak in an '83 300D. The first one was the pressure switch on top of the dryer which is now fixed. I'm using UV dye to look for the leaks, and I've wasted four cans of Freon trying to find it under the hood. Can someone tell me the best way to find it under the dash since that must be where it is? Thanks, Gerry Archer '83 300D and 240D - Original Message - From: Peter Frederick [EMAIL PROTECTED] To: Mercedes Discussion List Mercedes@okiebenz.com Sent: Saturday, June 10, 2006 3:36 PM Subject: Re: [MBZ] DIY AC repair in modern times Isobutane/propane refrigerant will work very nicely. However, if you have a leak, air leaks in while the hydrocarbons leak out, and you can get an explosive mixture fairly easily. The result can be a detonating compressor (don't laugh, I've seen it). You also risk a large explosion if you have an accident that punctures the condenser. You must indeed charge by pressure, adding 2.2 lbs of propane will definitely burst something. When whatever it is ruptures, you can get a propane/air explosion. R134a isn't much more expensive, is inert, and conversion isn't that hard. Peter ___ http://www.okiebenz.com For new parts see official list sponsor: http://www.buymbparts.com/ For used parts email [EMAIL PROTECTED] To Unsubscribe or change delivery options go to: http://okiebenz.com/mailman/listinfo/mercedes_okiebenz.com -- No virus found in this incoming message. Checked by AVG Free Edition. Version: 7.1.394 / Virus Database: 268.8.3/360 - Release Date: 6/9/2006
Re: [MBZ] DIY AC repair in modern times
If you convert to 134-A can you then go back to R-12 using your 134-A set of gauges? Not easily, and not legally. The fittings are all wrong for filling. The oils are mutually incompatible. I back-converted one of our 560 SL's, the fitting adapters just unscrewed. Getting that evil POS oil out of the compressor was difficult. I didn't do the complete flush before putting in mineral oil. Should have, but was getting tired, and you can't flush the drier, nor can you flush the evaporator without removing the expansion valve. R-134-A doesn't do a very good job of cooling my MBs. No, it doesn't. For a variety of reasons. (It perhaps could be made to work better, but longevity is also an issue.) I'm currently trying to find a second leak in an '83 300D. The first one was the pressure switch on top of the dryer which is now fixed. I'm using UV dye to look for the leaks, and I've wasted four cans of Freon trying to find it under the hood. This is a perfect example of where/why I use a test refrigerant. As a bonus, if you smell gas in the passenger compartment you know you have an underdash leak. Can someone tell me the best way to find it under the dash since that must be where it is? UV dye? Soapy water? Smell? Process of elimination? -- Jim
Re: [MBZ] DIY AC repair in modern times
All the connections are sealed with o-rings, and there are four on the expansion valve. I would guess that is where your leak is, and it may be slow enough that not much oil will blow out with the freon. I replace all the 0-rings with new green ones when changing a system over. Don't forget to check the compressor, too -- the hose junction on the later models tends to leak, as does the ffront seal and the piping manifold to compressor body on the Nippondenso conpressors. On my TE, the leak at the manifold to body was the high side o-rings, and the oil was on the block side, invisible until I removed the compressor.\ You can go back, but you really need to flush the oil out properly. Most undercooling problems are a result of overcharging -- R134a is lighter than R12, only put in 80 to 85% of the weight -- otherwise you get high suction side pressures and low cooling. Peter
Re: [MBZ] DIY AC repair in modern times
Isobutane/propane refrigerant will work very nicely. However, if you have a leak, air leaks in while the hydrocarbons leak out, and you can get an explosive mixture fairly easily. I do not see how a charged system can get _any_ air in it. I have never observed low-side pressure that dropped below atmospheric pressure if it was at all working correctly. If you let it get extremely low on charge, perhaps. But it would have stopped cooling long before this point, and should have tripped the safety switch anyway. It's not like you wouldn't have had your warning. Water doesn't flow uphill, after all. You also risk a large explosion if you have an accident that punctures the condenser. A rapid decomp of an R134A-filled condensor is also quite flammable. The oil spray is the big component, but you add the extremely toxic combustion products of the somewhat-combustible (!) refrigerant to the party. R134a isn't much more expensive, is inert, and conversion isn't that hard. All somewhat true. It's the nasty side-effects that are the problem. (It doesn't work well, it doesn't last long, the required oils are _not_ inert, and correcting it afterwards is made considerably more difficult.) -- Jim
Re: [MBZ] DIY AC repair in modern times
Don't forget to check the compressor, too -- the hose junction on the later models tends to leak, as does the ffront seal and the piping manifold to compressor body on the Nippondenso conpressors. The ND compressor has 6 O-rings, four at the manifold/body interface and two more where the hoses attach. There was a tremendous leak at the manifold on our latest 560 SL, where the _black_ O-rings of the 'converted' system were chewed. (It looked like mechanical rather than chemical degradation, but I've no experience with that to compare to.) It is an extremely obvious bit of crappy conversion, no doubt done at full price. Most undercooling problems are a result of overcharging -- R134a is lighter than R12, only put in 80 to 85% of the weight -- otherwise you get high suction side pressures and low cooling. Also, unless you've removed all the mineral oil (extremely difficult to do) you've left a large indigestible lump of oil in the system, where it can puddle and coat things to prevent heat transfer. It's immiscible in R134A, which is why you have to replace the oil when you convert. Most conversions, of course, don't replace the oil --- they just _add_ more new oil. -- Jim
Re: [MBZ] DIY AC repair in modern times
I am going to Replace the compressor, Dryer, under hood AC lines Easy-squeezy! and the expansion valve (bummer) in my 85 300SD. So sorry to be you! After I reassemble it I intend to evacuate it. I have a 1HP Alcatel 2 stage lab Vacuum pump. And get it down to 100 microns or so .. Vast overkill, and the pressure will never get that low due to the oil boiling slightly. But that won't hurt any. Not having R12 anymore I intend to put about 5 to 10 PSI of dry nitrogen in the system so it is not trying to draw out side air while I am waiting to get it charged (logistically it could be about a week) I will have the AC compressor unplugged to prevent unfortunate events. That sounds reasonable. You can go up to 100 psi or more with no ill effects. That might help to show up any small leaks. Now the system will have no oil in it. Is it acceptable the have the AC shop use the oil charge or should I try to find some oil in a bottle Just let them do it, I can't imagine they'll bill all that much. It's just oil, after all (of the correct sort), and something they should have on hand. When I open it I have been told to look for 'mud' and if it has it, it will need to be purged ..Sugestions . If the hose from the compressor is full of gunk it's because the old compressor grenaded and put shrapnel all through the system. That can be difficult to completely remove, and if any is left it will take out the new compressor quickly. Given your other replacements, a new condenser might not be a bad way to go in that case, as it's immediately downstream from the compressor. The remainder of the system would need to get a good flushing too. My AC stories: http://cathey.dogear.com/efair.html http://cathey.dogear.com/cwair.html Deep vacuuming app note: http://www.jbind.com/tech_info/pdf_docs/DeepVacArticle.pdf -- Jim
Re: [MBZ] DIY AC repair in modern times
I am going to Replace the compressor, Dryer, under hood AC lines Easy-squeezy! and the expansion valve (bummer) in my 85 300SD. So sorry to be you! I was told to do this, The last time I had a gauge set on the AC system it had a lo side pressure of about 20 at idle and very low hi side. The high side would come up at about 3000 rpm the lo side would read vacuum 15- 20 inches or so. That is when I got the car. The ac would sort of function on n a day when you did not really need it. I have had the car for 2 years and don't turn on the Air I don't know yet if the compressor decided to mimic a fragmentation grenade yet. I was hoping to be lucky and just have a weak compressor. This could make the repair easer. When I get the system open what do I look for to determine if it is contaminated Maybe I could get lucky and not replace the expansion valve? George Larribeau Dallas, Texas 1985 300SD 190K 1987 HD FLHTC 86K 1984 Motoguzzi Cal -2 80K 1972 Motoguzzi Ambassador LOTS 1965 Chevy C-10 pick up truck lots of miles 3rd small block ..(Extra Ugly,but runs) 1993 BMW 323i 115K (Wife's Car) 1967 BMW R50/2 (Wife's MC, currently in a Basket)
Re: [MBZ] DIY AC repair in modern times
Maybe I could get lucky and not replace the expansion valve? If it's just plugged and there's not a hose full of crap coming out of the compressor (indicating that it was the source of pluggage), likely you don't need to replace it either. -- Jim
Re: [MBZ] DIY AC repair in modern times
Maybe I could get lucky and not replace the expansion valve? If it's just plugged and there's not a hose full of crap coming out of the compressor (indicating that it was the source of pluggage), likely you don't need to replace it either. Now this is very obvious crap right ? ( can be easily identified ?) George Larribeau Dallas, Texas 1985 300SD 190K 1987 HD FLHTC 86K 1984 Motoguzzi Cal -2 80K 1972 Motoguzzi Ambassador LOTS 1965 Chevy C-10 pick up truck lots of miles 3rd small block ..(Extra Ugly,but runs) 1993 BMW 323i 115K (Wife's Car) 1967 BMW R50/2 (Wife's MC, currently in a Basket)
Re: [MBZ] DIY AC repair in modern times
Maybe I could get lucky and not replace the expansion valve? If it's just plugged and there's not a hose full of crap coming out of the compressor (indicating that it was the source of pluggage), likely you don't need to replace it either. And I should have been more clear that I'm talking about the compressor here. If it ain't broke don't fix it! There are really only two places where plugging can occur, ignoring physical damage to a line. The expansion valve, and the receiver/drier. These both feature screens and/or small orifices. If the drier's desiccant bag breaks it can travel downstream and plug up the expansion valve. Now this is very obvious crap right? (can be easily identified?) I should think so. I have personally never seen it, but the term 'black death' has been used a lot. -- Jim
Re: [MBZ] DIY AC repair in modern times
And I should have been more clear that I'm talking about the compressor here. If it ain't broke don't fix it! I have repaired non-broken things before. It's funny (many months after the fact) because it does usually wind up being broke after the repair. -- The reason that I thought that the compressor is bad is: At Idle the LO side is about 24 Psi ( or something, it matched a listing in a book) The HI side would not make 100 Psi (75 ?? don't remember). As the RPM is increased 3 to 4 K the HI side would jump up to over 200 Psi. The LO side would be 15 to 20 inches vacuum. The gauges seemed very responsive to RPM. Back off on the RPM, the HI side drops and LO side comes right back up. I will put a set of gauges on it this weekend and document the observations. What should I look for? This observation is from memory and most likely somewhat flakey. 20 years ago I worked on refrigeration in lab equipment however the compressors run at fixed RPM. Switched on and off for temp control. Now this is very obvious crap right? (can be easily identified?) I should think so. I have personally never seen it, but the term 'black death' has been used a lot. -- Jim But I don't what to go on the cart George Larribeau Dallas, Texas 1985 300SD 190K 1987 HD FLHTC 86K 1984 Motoguzzi Cal -2 80K 1972 Motoguzzi Ambassador LOTS 1965 Chevy C-10 pick up truck lots of miles 3rd small block ..(Extra Ugly,but runs) 1993 BMW 323i 115K (Wife's Car) 1967 BMW R50/2 (Wife's MC, currently in a Basket)
Re: [MBZ] DIY AC repair in modern times
The reason that I thought that the compressor is bad is: At Idle the LO side is about 24 Psi ( or something, it matched a listing in a book) The HI side would not make 100 Psi (75 ?? don't remember). Both pressures are low. Compressor _could_ cause this, but it sounds undercharged. As the RPM is increased 3 to 4 K the HI side would jump up to over 200 Psi. Still a bit low. I push 300 psi when charging with my test refrigerant on a hot day. But what I'm really doing is matching the _temperature_ scale on the R12 gauge to the temperature of the high-side fitting (while trying to keep it under 300 psi, while making sure the low-side hovers above freezing, engine at 2000 rpm). A dead compressor couldn't do this. The LO side would be 15 to 20 inches vacuum. Also too low. (Translation: the compressor is being too effective for current conditions.) Undercharged? Does not sound like a dead compressor to me. What should I look for? This is still R12? If the sight glass is frothy the system is definitely undercharged, and pressures _will_ be low. Are you _sure_ that there's anything more wrong than it's just undercharged? The systems (all of them) do leak a little, which is why R12 systems were built to hold an excess charge. Got them past the warrantee period before they stopped cooling. Most of our cars require charging annually now. But the test refrigerant is both cheap and benign. -- Jim
