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Jerry Newton
Jerry Newton, Cadillac Technician
Category: Cadillac
Satisfied Customers: 4413
Experience:  ASE Master Technician, L1, Master GM Technician. Over 20 years of bumper to bumper GM experience.
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I have a 1992 Cadillac De ville. The a/c quit. i am trying

Customer Question

i have a 1992 Cadillac De ville. The a/c quit. i am trying to check the relay because fuses are good and no power to limit switch. The relay box does not show me which one it is. Does anyone have a relay box diagram and a wiring diagram for this car?
Submitted: 1 year ago.
Category: Cadillac
Expert:  Jerry Newton replied 1 year ago.
Does the "Service A/C" light work on the dash during bulb check, and/or is it illuminated when you start the car?
Customer: replied 1 year ago.
I will check tomorrow because Dad is at work now, but I do not think it has a light on at all.
Expert:  Jerry Newton replied 1 year ago.
There is a light equipped on the car, but the bulb may be missing or burned out. I would be checking trouble codes next, because the BCM will disable AC for low refrigerant, and set a code. This would be the most common scenario. Do you know how to check for codes on this car? No tools necessary. I can teach you if you like.
Customer: replied 1 year ago.
it full of r134a we had done a complete change over in March
Expert:  Jerry Newton replied 1 year ago.
Understood. However, if this trouble code is set for low refrigerant (whether actually true or not), the compressor will not reengage until the code is cleared. First step has to be checking for trouble codes, since the BCM controls the compressor, and the BCM can prevent compressor operation. Do you know how to read trouble codes?
Customer: replied 1 year ago.
no codes, no power to a/c compressor
Expert:  Jerry Newton replied 1 year ago.
No body controller codes? Did you check using a scan tool or onboard diagnostics?
Customer: replied 1 year ago.
snap- on Solis. no BCM codes
Expert:  Jerry Newton replied 1 year ago.
Dealer techs never use scan tools on these cars, for good reason: scan tools notoriously report no codes when there are codes stored. The onboard diagnostics are much more comprehensive. Sit in the driver's seat, key on, engine off. Press and hold OFF and WARMER until everything lights up, then release the buttons. After a few seconds, watch the fuel data center. It will start reading out trouble codes. By way of example, you should see things like E.1.2, E.5.2, F.3.7, etc . Write down what you see. When it's done, it will say 7.0.0. At that point you can just shut the key off.
Customer: replied 1 year ago.
ok started .8.8.8 the F11 then F48 then .7.0
Expert:  Jerry Newton replied 1 year ago.
OK, F48 is the low refrigerant code. Enter diagnostics again, and wait until you get to .7.0. When you do, press and hold OFF and BLOWER LO buttons (the blower lo button is the second one from the right). This will clear BCM codes. Then, your compressor should start working for you after you cycle the key.
Customer: replied 1 year ago.
Did clear codes but a/c compressor did not cycle
Expert:  Jerry Newton replied 1 year ago.
OK, at least we have the BCM back on board, trying to make it work. Check to make sure no BCM codes are set again, before continuing on to find the problem. My recollection is that the AC compressor fuse is under the right side of the dash, on a small fuse block. Have you located that yet?
Customer: replied 1 year ago.
#7 in fuse box. all good. No BCM codes
Expert:  Jerry Newton replied 1 year ago.
OK, what do you have, no ground to the compressor relay? Is the AC system still charged? If the low and high pressure switches don't close, the compressor won't run, which means if there is not enough refrigerant in the system, you won't have compressor operation. Put a test light to the relay, you should have power on two legs of it, and ground from the BCM on one leg. Use the diagram on the side of the relay to figure out which pin is which.
Customer: replied 1 year ago.
do you know which relay it is? there are 2 fuse boxes sitting over the top of 4 relays on back of engine firewall when standing in front of car. Which one of the 4 is it?
Expert:  Jerry Newton replied 1 year ago.
Yes, here is a drawing that shows the relay location.
Customer: replied 1 year ago.
I will check it out in morning. Too hot going Home. Thanks
Expert:  Jerry Newton replied 1 year ago.
Sure, let me know how it turns out.
Customer: replied 1 year ago.
tested relay, 2 wires hot and 1 ground with key off, turn key on and a/c on I have 3 wires hot and 1 ground.
Customer: replied 1 year ago.
also charge on a/c with a/c off. high side 140psi, low side in retard over 125psi. This is with the engine not running and engine running.
Expert:  Jerry Newton replied 1 year ago.
Two wires should be hot. A third wire goes to the compressor clutch. And the fourth wire goes from the ECM to the relay, this is the control wire. I cannot find a schematic for this old gal, so I don't have wire colors to work with. If you test the wire going to the compressor with key on, you'll probably find that it has power, because the other side of the compressor coil is attached to battery voltage and the current simply runs through the coil and to this wire. It's the fourth pin I am concerned with, it should go to ground when the ECM turns on the AC compressor. Lacking wire colors, you'll have to rely on the diagram on the side of the relay. Pins 85, 86, 87, and 35 are the ones you're looking for here.