billschroeder5842

I need a little direction with trouble shooting my 91 ZR1 Air conditioning.

I bought the car a couple of weeks ago with the AC non functional. All vent doors operate, heat works. Buttons flash indicating low pressure.

I took it to a AC guy who has done work for me in the past who is knowledgeable and honest.

He checked the pressure and said that was good, the system was converted to 134, was full of Freon and with no leaks. He "jumped" the compressor and it kicked on. He also went to the passenger side and jumped what looked like a relay switch and the compressor popped on.

He spend about 45 minutes with it and said that I most likely have electrical issues that he needed to fully diagnose. He asked me to bring it next week when he could spend more time with it. He asked for me to bring my electrical FSM.

So.... is there any "typical" electrical gremlins for him to check? The car has not (not) be bubba'd as far as I can see. Sure electrical could be one of a gazillion things, but are there "common" bugs that we can attack first?

BTW... my stereo is out and Ill be doing a CDM (gulp) and amp swap on the Bose Gold this weekend-- I take it there is no linkage between the AC and radio if the CDM is junk??

Thanks!

ddahlgren

Bad low pressure switch? My 91 coup had a bad switch that PO jumped and hid from me when selling the car.

billschroeder5842

So, I did a bit of trouble shooting (press the fan buttons and then Auto) and got 09 code for low Freon. However, the tech found that the system was fully loaded and properly presured.

Any thoughts? I'm following the FSM, but wondering if anyone has had a similar situation and can help me short cut.

ddahlgren

Why not just trace the circuit from the ECU to the relay.

gmboileau

Once Code 9 is set the code has to be cleared before the compressor will kick in.

Disconnect the negative battery cable for a short time ......it should turn off the flashing and clear the code. If the system is not low on charge it should start up.

WVZR-1

IF it's got a sufficient charge and IF there are no other issues this should certainly "clear" the C68 control logic.

It's actually the 1st step in the FSM for 09 DTC diagnostics.

ddahlgren

C68 only knows what the sensors tell it.

bjankuski

When he jumped the low pressure switch the compressor kicked in, that is the bad component (Since he checked the actual Freon pressure and it was good). Replace the switch and all will be fine. (That switch is telling the car that the Freon is low and not allowing the compressor to kick in).

gmboileau

The radio issue that the OP mentions is another clue...if the 15amp CTSY fuse is installed when the ignition is on it can cause a false code in the AC programmer. Disconnecting the battery for a short time clears that issue....quick and easy. If the code returns then other issues need to be explored.

WVZR-1

While i agree that it's likely the issue I don't think you just throw a switch at it. It seems the fellow approached the diagnostics realistically and asked for the FSM to complete the diagnostics. With the FSM he can check the switch for correct operation. The OP mentioned "honest" and has previous experience with so I believe you let him finish.

billschroeder5842

*UPDATE*

Thanks everyone... I followed your advice and the FSM and pulled the negative cable and followed the "reset" procedure and it works!

I turned the car on/off a few times and pushed different settings and could hear the compressor go on/off and the fan would go on/off in the recirculate setting. The AC was blowing at 45 degrees, idling in my garage. The fault code disappeared.

This is my first C4 (I also have an 82 C3) and they are WAY more electrical and sensor oriented than I'm used to. Thanks for the direction.

I will check the CTSY fuse later today just to be sure.