the a/c compressor isn't turning on. Its not getting any electricity when the control panel is on auto and set on 60 degrees. Can't find the relay for the compressor and my shop manual doesn't tell where it is either. Where is the compressor relay located?? Already did the system check, holding down the up and down fan control buttons for 5 seconds but it reads -00 (no codes).Its a '90 L98 coupe. Getting ready to take the control panel out and clean the contacts. Any suggestions?? The compressor isn't locked up. Thanks in advance

 

I am no auhority...but did you try jumping the low preasure switch to
see if maybe the freon was low??just my two cents.

 

[QUOTE=Great White North]I am no auhority...but did you try jumping the low preasure switch to
see if maybe the freon was low??just my two cents. [/QUOTE

Thanks for the suggestion, will try it.

 

Yep, if the charge is low, the compressor clutch won't get voltage. Blame it on the low pressure switch!

 

For your Year, you may need to disconnect the battery to get it running again. ECM controls compressor operation and monitors the low pressure switch for frequent cycling (on/off times which if it's off and on at a fairly high frequency, i to the ECM that the charge is low).

 

For your Year, you may need to disconnect the battery to get it running again; albeit, it may only be for a brief second or two if it's low on gas. The ECM controls compressor operation and monitors the low pressure switch for frequent cycling (on/off times). Too much cycling, and it shuts the system down until the problem is corrected. It also monitors a pressure switch on the high side which tells it electronically, what the operating pressure is. That switch, basically a thermistor, gets a 5 volt reference from the ECM and the higher the pressure, the higher the voltage return to the ECM (each volt is equal to 100 psi of gas). Should the ECM see something less than about .8 volt; or more than 4 volts (meaning it's about to blow up), it won't ground the compressor relay and that will also shut it down. In any event, if it's been cycling frequently and/or the pressure switch is outside of it's operating range, it should set a trouble code which you can access through the control panel or with a Scanner. To get it running again; either to test it or to recharge it, you've got to clear the code and you can either remove power from the ECM or disconnect the battery. Then, if you're going to recharge it (assuming there's something in it), put a paper clip across the low pressure switch harness terminals and that will keep it from cycling so it won't shut down and reset the code. If you just want to test it, you can do this and if there's any gas in it, you should see some ice on the evaporator outlet. If it's completely empty, then you're going to have to get a can in it before you try and start it and the only way to do that is to vacuum the system down and let the vacuum pull in the first can. Then, put your paperclip across the low pressure switch harness terminals and let the system pull in the balance of the charge.

As to the compressor relay, location should be shown in your owner's manual or look for it in one of the fuse boxes under the hood (assuming your Year puts a couple of the fuses under there).

 

Thanks very much!!!! Will try that this afternoon