Re: [MBZ] A/C problem on 126
I would be surprised if the vacuum had anything to do with the A/C blowing warm, it is most likely only used for the diverter flaps. What I suspect may be happening is that when you floor the accelerator it operates a switch to disconnect the compressor, thereby giving you full power. My 87 300TDT works that way. -- SANTÉ Doug Quance Consciousness: That annoying time between naps. 90% of being smart is knowing what you're dumb at.
Re: [MBZ] A/C problem on 126
On Jun 21, 2006, at 4:03 PM, Donald Snook wrote: The only time I have noticed this phenomenon was climbing the hills. It worked great on flat runs. Any thoughts? There are safeguards that cut the AC out when temp is too high, pressure drops or engine is at very high revs. Did you observe the gauges? Was the tranny kicked-down? Johnny B. I Mac Therefore I am
Re: [MBZ] A/C problem on 126
Re: my question about the a/c cutting out on hills, Johnny B. wrote: There are safeguards that cut the AC out when temp is too high, pressure drops or engine is at very high revs. Did you observe the gauges? Was the tranny kicked-down? The engine was certainly at high revs. I was making this trip at 80-85 mph. This car has the 103 engine and the 126 (SEL) is a big heavy car, so at that speed I am always approaching 4000 rpm. I don't recall whether the transmission had kicked down, but I assume that it had because I was climbing a steep hill. Donald H. Snook McDonald, Tinker, Skaer, Quinn Herrington, P.A. 300 West Douglas P.O. Box 207 Wichita, Kansas 67201 0207 Tel. (316) 263-5851 This confidential message may be subject to the attorney-client privilege or protected by the attorney work-product doctrine. If you have received this message in error, please delete it and notify me.
Re: [MBZ] A/C problem on 126
Marshall wrote: There is another sensor that will cut off the AC compressor when the coolant temperature approaches the safe temperature limit. Either of these COULD be exceeded when climbing a hill. There MAY also be a pedal switch that cuts off the compressor when the accelerator pedal approaches the floor. This was often installed in cars with smaller engines (relative to the weight of the car). If you mean that the blower speed changes or the air comes from different vents, then I have NO idea. The air is not really getting warmer and I can still hear the blower motor running, but I am not getting good flow from the center vents. The symptom has not repeated itself in over a week. Perhaps it was just too hot and I was pushing it too hard. Donald H. Snook 1990 300SEL 128K
Re: [MBZ] A/C problem on 126
The engine was certainly at high revs. I was making this trip at 80-85 mph. This car has the 103 engine and the 126 (SEL) is a big heavy car, so at that speed I am always approaching 4000 rpm. I don't recall whether the transmission had kicked down, but I assume that it had because I was climbing a steep hill. If _you_ floored it the kickdown switch (on that model) could have turned off the AC compressor. But that doesn't affect how the blower and vents work. If anything the fan speed will _increase_ as it starts blowing vent air, assuming it's warm out and the cabin tends to get too hot without AC. That's what our SDL does. But if the tranny downshifted by itself that mechanism isn't operative. -- Jim
Re: [MBZ] A/C problem on 126
This is purely a vacuum storage problem, could even be normal if your time on the hill exceeds the volume of vacuum storage. The AC system normally _consumes_ no vacuum, so this shouldn't happen regardless. That is, when a pod changes state there is a consumption of vacuum, but steady-state there should be no draw. There would need to be a leak in order for this to be happening. -- Jim
Re: [MBZ] A/C problem on 126
If the dash vents switch to defrost at full throttle, you have a vacuum leak -- there is a tank that holds vac for the system, but leaking supply lines and/or leaking servos will cause it to cycle back to defrost at wide open throttle. Usually this is leaking servos, as they require condsiderably more vac that the system usually provides at WOT. As for the temp rise, you should check the AC pressures at high rpm (3000 -- only for a few seconds, please, the engine doesn't like it!). Either excessive high side OR too low low side pressures will cut the AC off. A faulty expansion valve will cause very low pressure by preventing freon flow, and this can also cause the compressor to stop. Usually this means a clog. Air in the system will cause excessive high side pressure hot. And, a bad evaporator temp sensor will cut the compressor off inappropriately, too! However, the very first thing I would do is replace the belt -- a slipping belt will cause the AC compressor to drop off line until the engine is restarte. This is to prevent a compressor lockup from making the engine inoperable. I don't know if there is a WOT cutout for the AC compressor. That would be unusual, as even the old diesels don't have one! Peter
Re: [MBZ] A/C problem on 126
Donald Snook wrote: The air is not really getting warmer and I can still hear the blower motor running, but I am not getting good flow from the center vents. The symptom has not repeated itself in over a week. Perhaps it was just too hot and I was pushing it too hard. Sounds like vacuum leak (probably an actuator has cracked) and without high vacuum to overcome the leak, the system defaults to defrost. The things I described would shut off the compressor - not change the air distribution. Marshall -- Marshall Booth (who doesn't respond to unsigned questions) der Dieseling Doktor [EMAIL PROTECTED] '87 300TD 182Kmi, '85 190D 2.0 161Kmi, '87 190D 2.5 turbo 237kmi, '84 190D 2.2 229Kmi (retired)
Re: [MBZ] A/C problem on 126
Donald Snook wrote: I took a trip 300 mile trip the other day in my 1990 300SEL (128K) and I noticed that when I was climbing a long steep hill (steep for Kansas, not steep for anywhere else) my a/c would stop blowing very hard. It was a very hot day and when the a/c would stop blowing it was noticeable. When I crested the hills and proceeded down the hill the a/c would return full blast. This was all at 75-85 mph. Could this be a vacuum problem? Probably a minor vacuum leak. At large throttle openings manifold vacuum drops to almost nil. To allow the HVAC system to still function properly, there's generally a reservoir somewhere and a check valve to provide a steady vacuum source. If the check valve is bad or there's a leak somewhere, the vacuum will bleed down to nothing when you have your foot in it for a long stretch, and the HVAC flaps will go to their 'default' positions.
Re: [MBZ] A/C problem on 126
very cold. The only time I have noticed this phenomenon was climbing the hills. It worked great on flat runs. Any thoughts? Yeah, could be vacuum loss. Does cold air start coming out of the defrost vents at this time? -- Jim
Re: [MBZ] A/C problem on 126
Donald Snook wrote: I took a trip 300 mile trip the other day in my 1990 300SEL (128K) and I noticed that when I was climbing a long steep hill (steep for Kansas, not steep for anywhere else) my a/c would stop blowing very hard. It was a very hot day and when the a/c would stop blowing it was noticeable. When I crested the hills and proceeded down the hill the a/c would return full blast. This was all at 75-85 mph. Could this be a vacuum problem? Or something else? The a/c works great otherwise - very cold. The only time I have noticed this phenomenon was climbing the hills. It worked great on flat runs. Any thoughts? If you are talking about how cold the air is, here are several possibilities: There is a pressure cutoff that will cut off the compressor when the high pressure exceeds some limit. This could easily happen in a system that's been converted to R-134a. There is another sensor that will cut off the AC compressor when the coolant temperature approaches the safe temperature limit. Either of these COULD be exceeded when climbing a hill. There MAY also be a pedal switch that cuts off the compressor when the accelerator pedal approaches the floor. This was often installed in cars with smaller engines (relative to the weight of the car). If you mean that the blower speed changes or the air comes from different vents, then I have NO idea. Marshall -- Marshall Booth (who doesn't respond to unsigned questions) der Dieseling Doktor [EMAIL PROTECTED] '87 300TD 182Kmi, '85 190D 2.0 161Kmi, '87 190D 2.5 turbo 237kmi, '84 190D 2.2 229Kmi (retired)
