Re: [MBZ] 201 HVAC
Any caps in the works that could have failed, or had their ESR rating fluctuate? Not just electrolytics. There are _lots_ of analog components in there. Was hoping for a 'common cause' kind of idea. All fourteen op-amps had what looked to be good outputs at least, so I'm not expecting silicon process problems. No conformal coat. If I had a schematic I'd probably be done by now, but making one would be a real PITA. -- Jim ___ http://www.okiebenz.com For new and used parts go to www.okiebenz.com To search list archives http://www.okiebenz.com/archive/ To Unsubscribe or change delivery options go to: http://mail.okiebenz.com/mailman/listinfo/mercedes_okiebenz.com
Re: [MBZ] 201 HVAC
The HVAC system in my '83 300D was doing weird things, even after
I replaced all the units, pushbutton, temp controller, and fan speed
controller units.
Having had bench experience with the weird things low voltage can cause
a solid state system to do; (especially old solid state systems), I used a
relay and fed 12v directly to the fanspeed control module even though
voltages were normal at various points in the system. Power to the
pushbutton module and the temperature module remained the same.
The system has been working well with no problem for several months.
I ran a piece of 14ga drop cord from the 12v bus bar on the right fender
throught an existing grommet in the firewall to power the fan speed
controller
and put an inline fuse holder next to the buss.
The headlight relay coil connects to the power supply from terminal
#8(16amps) on the fuse module and the 12v line from the buss and the
positive line from the controller connect to the relay contacts. Drop cord
has a very tough covering and I've found it to be ideal in running extra
wiring; especially through the firewall since one size of grommet fits it
snugly.
If your system is anything like a 123, splitting the power supply might be
worth trying.
Gerry
'83 300D and 240D
---
From: Jim Cathey j...@windwireless.net
Anybody have any in-depth experience with the early ('86) 201 HVAC
controller? Mine refuses to turn off the water valve so it's
always heating, and I've 100% proven that it is the HVAC box
that's not activating the vacuum solenoid, everything downstream
of there works perfectly if it's jumpered manually. The only
other symptom is that the automatic AC compressor setting is
equivalent to off, you have to use the ON/DEF AC button to turn
it on. Other than that the system seems to be working properly.
I've followed my own checklist to ensure that all the inputs to
the unit are reasonable, specifically the four analog inputs
(3 temps and the blend flap feedback pot) appear to be OK.
A junkyard unit (spare) does _exactly_ the same thing.
Coincidence? Unrecognized external problem? Common failure?
I've resoldered it, and dug far enough into the thing to prove
that it's not a fried output. (If I ground the - input of
the op-amp that ultimately drives the water valve it will engage
the valve and turn off the auxiliary pump, as it should. It's
a control problem of some sort. On the bench the blend flap
and AC control outputs work, and react to the external inputs
and the control dial. Just no heat-off ability.
-- Jim
___
___
http://www.okiebenz.com
For new and used parts go to www.okiebenz.com
To search list archives http://www.okiebenz.com/archive/
To Unsubscribe or change delivery options go to:
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Re: [MBZ] 201 HVAC
Any caps in the works that could have failed, or had their ESR rating
fluctuate? Not just electrolytics.
Any critical feedback resistors that could have drifted over time?
Did you throw the scope on the thing at various points along the signal
paths, checking each stage?
Conformal coat changing capacitence due to water uptake?
Just some random musings.
Walt
On Aug 4, 2011 11:25 AM, Jim Cathey j...@windwireless.net wrote:
Anybody have any in-depth experience with the early ('86) 201 HVAC
controller? Mine refuses to turn off the water valve so it's
always heating, and I've 100% proven that it is the HVAC box
that's not activating the vacuum solenoid, everything downstream
of there works perfectly if it's jumpered manually. The only
other symptom is that the automatic AC compressor setting is
equivalent to off, you have to use the ON/DEF AC button to turn
it on. Other than that the system seems to be working properly.
I've followed my own checklist to ensure that all the inputs to
the unit are reasonable, specifically the four analog inputs
(3 temps and the blend flap feedback pot) appear to be OK.
A junkyard unit (spare) does _exactly_ the same thing.
Coincidence? Unrecognized external problem? Common failure?
I've resoldered it, and dug far enough into the thing to prove
that it's not a fried output. (If I ground the - input of
the op-amp that ultimately drives the water valve it will engage
the valve and turn off the auxiliary pump, as it should. It's
a control problem of some sort. On the bench the blend flap
and AC control outputs work, and react to the external inputs
and the control dial. Just no heat-off ability.
-- Jim
___
http://www.okiebenz.com
For new and used parts go to www.okiebenz.com
To search list archives http://www.okiebenz.com/archive/
To Unsubscribe or change delivery options go to:
http://mail.okiebenz.com/mailman/listinfo/mercedes_okiebenz.com
___
http://www.okiebenz.com
For new and used parts go to www.okiebenz.com
To search list archives http://www.okiebenz.com/archive/
To Unsubscribe or change delivery options go to:
http://mail.okiebenz.com/mailman/listinfo/mercedes_okiebenz.com
[MBZ] 201 HVAC
Anybody have any in-depth experience with the early ('86) 201 HVAC
controller? Mine refuses to turn off the water valve so it's
always heating, and I've 100% proven that it is the HVAC box
that's not activating the vacuum solenoid, everything downstream
of there works perfectly if it's jumpered manually. The only
other symptom is that the automatic AC compressor setting is
equivalent to off, you have to use the ON/DEF AC button to turn
it on. Other than that the system seems to be working properly.
I've followed my own checklist to ensure that all the inputs to
the unit are reasonable, specifically the four analog inputs
(3 temps and the blend flap feedback pot) appear to be OK.
A junkyard unit (spare) does _exactly_ the same thing.
Coincidence? Unrecognized external problem? Common failure?
I've resoldered it, and dug far enough into the thing to prove
that it's not a fried output. (If I ground the - input of
the op-amp that ultimately drives the water valve it will engage
the valve and turn off the auxiliary pump, as it should. It's
a control problem of some sort. On the bench the blend flap
and AC control outputs work, and react to the external inputs
and the control dial. Just no heat-off ability.
-- Jim
___
http://www.okiebenz.com
For new and used parts go to www.okiebenz.com
To search list archives http://www.okiebenz.com/archive/
To Unsubscribe or change delivery options go to:
http://mail.okiebenz.com/mailman/listinfo/mercedes_okiebenz.com
Re: [MBZ] 201 HVAC
I have several of these with the following behaviors:
Full heat all the time
Won't turn on AC
Won't turn on heat
The one in my car does a pretty good job but reacts slowly.
Seems like they fail all sorts of ways.
I'll send you my box of spares if you want. If you can make 2 of them work
right send me one and we'll call it good. If you can only make one work right
keep it for yourself. If you can't make any work, add them to the scrap pile.
-Curt
Date: Thu, 4 Aug 2011 08:25:51 -0700
From: Jim Cathey j...@windwireless.net
To: Mercedes Discussion List mercedes@okiebenz.com
Subject: [MBZ] 201 HVAC
Message-ID: 09ceacb8-beae-11e0-9000-000502d9a...@windwireless.net
Content-Type: text/plain; charset=US-ASCII; format=flowed
Anybody have any in-depth experience with the early ('86) 201 HVAC
controller? Mine refuses to turn off the water valve so it's
always heating, and I've 100% proven that it is the HVAC box
that's not activating the vacuum solenoid, everything downstream
of there works perfectly if it's jumpered manually. The only
other symptom is that the automatic AC compressor setting is
equivalent to off, you have to use the ON/DEF AC button to turn
it on. Other than that the system seems to be working properly.
I've followed my own checklist to ensure that all the inputs to
the unit are reasonable, specifically the four analog inputs
(3 temps and the blend flap feedback pot) appear to be OK.
A junkyard unit (spare) does _exactly_ the same thing.
Coincidence? Unrecognized external problem? Common failure?
I've resoldered it, and dug far enough into the thing to prove
that it's not a fried output. (If I ground the - input of
the op-amp that ultimately drives the water valve it will engage
the valve and turn off the auxiliary pump, as it should. It's
a control problem of some sort. On the bench the blend flap
and AC control outputs work, and react to the external inputs
and the control dial. Just no heat-off ability.
-- Jim
___
http://www.okiebenz.com
For new and used parts go to www.okiebenz.com
To search list archives http://www.okiebenz.com/archive/
To Unsubscribe or change delivery options go to:
http://mail.okiebenz.com/mailman/listinfo/mercedes_okiebenz.com
Re: [MBZ] 201 HVAC
I'll send you my box of spares if you want. If you can make 2 of them work right send me one and we'll call it good. If you can only make one work right keep it for yourself. If you can't make any work, add them to the scrap pile. Hey, I'll take that deal! We're headed out for a week's vacation, but after we get back... Seems like these things are a lot less reliable than the two-piece ones in slightly older cars. Yes, their PB arrays were less reliable, but they were also easily fixed. I never had a Temperaturregler fail. I think I have one spare in the garage just in case, since we have five cars that use that system. (All five, btw, are working, or at least were working when last tried.) So far this thing's kicking my butt. -- Jim ___ http://www.okiebenz.com For new and used parts go to www.okiebenz.com To search list archives http://www.okiebenz.com/archive/ To Unsubscribe or change delivery options go to: http://mail.okiebenz.com/mailman/listinfo/mercedes_okiebenz.com
