Jibriggs

Hi all,

As stated, I am new here. I've lurked over the years to glean info for my various cars.
This is my 5th w124 (diesel) car and I am comfortable with just about anything in regards to working on them, however, this problem has me stymied.

It's a US 1995 E300D with 170k mi.

This car is new to me and I inherited it with the problem (and many others).

So, my problem is an intermittent acc system. Often, the AC compressor just turns on and stays engaged until I turn the car off. Sometimes the recirc light comes on and cannot be turned off. Also, the fan is ON always. When either of those conditions occur, the pushbutton unit becomes inop. There is never a time when the system functions normally. Hot air from the defrost and cold air from the center vents. I have to unplug the acc in order to drive since the compressor is engaged all the time....
Restart and all looks normal. Within 2 minutes of a cold start, the issue(s) return. On a hot start, it might be immediate.

At first I threw a new control into it (actually, 3 of them). It changed problems, but did not fix anything.
Under hood engine wiring harness is new. (Updated harness)
Strip fuse and all fuses are NEW.
Fan is operational and diode is good. (But not controlled by ACC .. just stays on until I unplug at brake booster)
I have followed the factory diagnostics for the climate system and not had conclusive results.
All sensors read good.
Interior temp fan is drawing air.


Would a bad vacuum block cause a fault? Testing for resistance was in spec, but I'm suspicious anyway.
Could a bad duovalve cause a system issue besides temperature control issues?

What other things might I look at?
I tried the blink tester, but it did nothing on my vehicle...

Thank you for your consideration. J

QVHK

Maybe the AC had been modified before as a quick fix and hence the problem never goes away and keeps haunting you. An always on or intermittent off and occasional normal symptoms are always caused by the failing AC Relay. You may also have multiple causes of your AC problem, like pressure switch or temperature sensors. Try one at a time to see if they would sort it. Here is a list of AC system parts that you may need:
http://www.pelicanparts.com/catalog/...VENTAC_pg1.htm

Jibriggs

Thanks QVHK,

I appreciate the list of possibilities and will certainly be buying something, I'm sure.

Just to be clear, I'm reposting the problem. It's not an A/C problem per se. The entire system is affected.

I purchased this car as a running project. After going thru the engine (full glow plug job incl reaming and prechamber cleaning, injector rebuild, new harness), I have a major gremlin in the HVAC/ACC system.

In any mode on the original pushbutton unit, the fan runs continuously at the same (mid) speed (3.3 volts at yellow wire) and heat is full on thru defrost ducts. Pushing buttons does NOTHING... On, off, whatever.

With a known good replacement unit, I have control over the flaps for about a minute after a cold start, then, the AC compressor engages and stays on regardless of settings all the while putting out full heat.

I understand that most of the components are switched on the ground side in this system, so, my theory is that one component is shorted.
I have followed the factory test procedure as best I can with a multimeter, but no love. All components check out fine.
As for the fan, I got in there, removed it, suspecting the relay. I changed it, and for testing bypassed the circuit, adding a fan controller pot. The fan works great, and I have independent control of it, but the acc is still inop.
I'm a rabid Diy'er, but I'm losing on this one.
Anybody have a similar issue?

Thanks,
J

Jibriggs

Oh, I should've said...

I tried a different klima relay as well. Same behavior..

QVHK

AS I said, the weird behaviour of your AC system is possibly caused by unknown modifications by the previous owner who would understand how to get it working properly, like sequencing or getting multiple parts on/off to turn on or cut the AC. Or maybe some of those coordinating parts (obviously non-OEM) have failed to work under the non-conventional set-up hence making maintenance and trouble shooting difficult. Would suggest you find a professional to get this sorted. Can't imagine driving without AC in summer.

Jibriggs

I hear ya.

So, yes, I do have finding a trusted professional to work on my car on my list.
The problem is that I haven't had anyone touch any of my vehicles ever (unless it was fabrication, or upholstery etc.)

So, since this car is a project, and I like punishment, I'm going to try a little longer.

The likely outcome is that I take it in...

In Seattle, I'm just as likely to use heat than ac. Good thing the car is making quantities of both hot and cold air simultaneously.

Recommendations​ for a good shop in my area anybody?

Regards,
J