AC Compressor Will Not Shut Off

[Jimmy535i]

My vehicle is a 1992 535ia (e34)

I have a problem with my AC system that I am trying to sort out.
When I turn on the AC. The compressor will come on. AC is ice cold.
When I turn off the AC , the AC compressor will
continue to run. It will run basically until I shut the car off.

I have completed the following work on the AC System:

Conversion to R134A. With New receiver drier.
The system is fully charged and has correct amounts of
R134A and PAG oil.

Installed new auxillary fan resistor after fuse #25 blew.
Auxillary fan is working.

I swapped the HVAC control panel with one that I know was working
in another vehicle. So I have eliminated that.

Has anyone had a similar problem? Or can offer some advice?
Could it be the AC Control module or some relay that is bad?

Thanks in advance for any Ideas.

[winfred]

the compressor relay is the one next to the position that i am pointing to, the climate control unit energizes the relay with a ground signal

[Jimmy535i]

Winfred....Thank you for your help. I will swap the relays and see if that does the trick.

[Javier]

shorted, any thermostat low speed auxiliary fan request will also trigger the A/C compressor.

Easy check: When A/C compressor refuses to shut down, remove Auxiliary fan low speed relay K21. If A/C clutch disengages, replace K21 relay diode (or complete relay, depending on your finances/abilities).

Javier

[Jimmy535i]

Thank you Javiar... I will swap this relay also

[winfred]

the compressor relay that i pointed out is probably not bad, that's just a good place to check out the system

Thank you Javiar... I will swap this relay also

[Jimmy535i]

I removed the AC relay and the AC compressor shut off. I swapped this relay with one from another vehicle and the AC compressor continues to run after the switch on HVAC control panel is turned off.

I think I have some more hunting to do.

Is it possible that the new auxillary fan resistor that I installed is either no good or
is it possible to wire this incorrectly.

[Jimmy535i]

Javiar. I removed the normal speed relay and the AC compressor continues to
run. I swapped this relay and I am still experiencing the same problem.

Could the resistor for the auxillary fan be the problem. I replaced this resistor
with a new one I got from BMW. Is it possible to install it incorrectly?

[winfred]

aux fan resister has nothing to do with the compressor, if you pull the relay i pointed out and the comp still has power something has probably shorted under the hood, the relay is triggered with a ground from the climate control unit under the dash

Javiar. I removed the normal speed relay and the AC compressor continues to
run. I swapped this relay and I am still experiencing the same problem.

Could the resistor for the auxillary fan be the problem. I replaced this resistor
with a new one I got from BMW. Is it possible to install it incorrectly?

[Javier]

and wire replacement in its place, there is no reason to have modified old wiring.

If I understood correctly, when you pull compressor relay, clutch disengages. So relay is getting a request (pin 86 of relay is grounded as posted by Winfred). There are only two ordinary ways to have this ground, either from Fan low speed relay if diode is shorted (you did pull and ground was not removed, so this one is discarded), or from climate control. Extraordinary way to have this ground includes damaged wiring.

The estrange thing here is that compressor (and obviously low speed auxiliary fan as they go together at compressor request signal) is not engaged as soon as you start the engine (per your post), this will be the case if a damaged wiring imposes a permanent ground to pin 86 on the relay. I feel the ground signal comes from Climate control and there is some other reason it is not removed. You told that climate control was already swapped, so should be OK.

In order to completely discard wiring damage, I would remove climate control and compressor relay, and check continuity to ground at compressor relay socket pin, corresponding to pin 86 of the relay. If continuity there, also remove auxiliary fan relays to discard they are providing it. If ground is still there, wiring should be checked looking for a damaged insulation and short to ground.

If no continuity to ground, the Climate control is requesting the compressor to be engaged, as even with Low speed fan relay removed, compressor refuses to stop.

You said compressor turn off when you turn off the engine, try turning it back on immediately to check if compressor stays off or go on immediately even not having turned A/C on. If so, turn back off engine, remove climate control and turn on again to check compressor status (this should be done in a very short time, so to keep things hot); if still engaged, I feel the wire short to ground is not permanent but a consequence of thermal issues in the wiring, it is not there until you start the compressor trough the climate control, and stays there even after climate control compressor request is removed, probably for a short period of time, after the engine is turned off.

On the other hand, may be some expert in IHKR/F3 can tell us if there is any sensor or signaling to Climate control that can request compressor on even after A/C is turned off. I doubt it.

Javier