Chevrolet Repair Questions? Ask a Chevy Mechanic for Answers ASAP
Hello I will help you with your question,
There are a couple of possibilities for this problem,
This is the manual system of controls?
First find the AC clutch relay in the underhood fuse block and use a paperclip to jump the #30 to the #87 sockets in the fuseblock. (Look on the underside of the relay for the numbers)
If the clutch clicks in when you turn the key to run then the compressor, the power to the compressor and the wiring for the compressor are good.
Let me know what you find and we will work the other side of the system if necessary
the relay is a small one and the numbers are 2 3
5 1 in that order
If you have a voltmeter or testlight check for voltage at the paperclip and if that is good check at the compressor connector.
The rear is the high pressure cutout and is not part of the circuit you are working on. so check the paperclip with the key on and if there is voltage there check the green wire at the compressor. If there is voltage to the compressor and the clutch does not pull in when you plug it in replace the compressor.
It's not reading any volts from the green wire
Then you have an open in the green wire between the #5 terminal of the relay and the compressor connector. This is a single piece of wire so look for any breaks in the harness and if you cannot find anything overlay a new wire. This takes care of the power to the compressor but to be sure of the repair you need to check the control side and be sure the PCM is turning the relay on by grounding the pin #1 of the relay.
The is a splice just where the wire from the compressor connector enters the main engine harness I would start looking there.
There are two sides to any circuit that has a relay in it. You have just diagnosed the power side that runs from the fuse through the relay contacts to the load (in this case the compressor) . The relay is controlled by the PCM (computer) which grounds pin #1 of the relay to turn it on (or to close the contacts so that power flows to the compressor)
For the PCM to ground the relay coil at pin #1 it has to be sure all conditions are correct. The AC switch on the dash has to be turned to on, the pressure of the cycling switch has to be above 40 psi and the high pressure switch on the back of the compressor has to show pressure below 425 psi. If all these conditions are met the PCM grounds the relay and the compressor is turned on.
By jumping the relay contacts with the paperclip you did the job of the PCM and found that the power was not reaching the compressor but was present at the relay. Double check that you have the correct pins jumpered and that you don't have power to the compressor connector then find the break in the wire. You may have to expose the wiring harness back to the relay box to find the break
Once you have power to the compressor you can install the relay and see if the compressor operates on command from the AC switch. If it does you are done. If it does not we will have to work to find which of the conditions the PCM does not like
Let me know what I can do to help you with this
It really doesn't matter which way the relay is installed for the four leg relays, I like to look at the tops and keep all the printing the same but when you turn it the contacts just swap ends so the connections remain the same.
I'm not sure what you mean by a connection from the panel to the plug? Do you mean you have a complete wire from the paperclip (installed as a jumper between the two corners of the relay sockets (3 and 5) or (#30 and #87)? If you do have a complete wire check for power at the paperclip and at the connector.
If the numbers ar in the corners and you have the wide flat side of the relay up with the legs pointing at your face and the 3 is in the upper right with the 5 in the lower left turn the relay 180 degrees so that the side that was pointing up is now down. The 5 will be in the upper right with the 3 in the lower left now. It doesn't matter as long as you start at the 3 or the 5 and use the paper clip to jump diagonally to the other corner.
Draw this out on paper if you are not sure