A/C electrical problems

[87GNSteve]

Bought car as a roller. Recently installed a rebuilt engine, trans etc. New: AC compressor, condenser, exp. valve, drier etc.
Vacuumed the system held great now when I try to charge the system and jump the pressure switch the fans go on, and then the wires get super hot at the point of going to melt if I left them the compressor clutch doesn't move.. I made a jumper with a 20 amp fuse and it pops in a few seconds. I swapped relays for another used on I had and same thing...
Help!

 

[TurboTdr3.8]

I have the same problem to a tee and I would like to know also what anybody has found .

 

[Turbo Negro]

If the wires are getting hot while jumping the pressure switch, there is power present with a high resistance. I would check the diode at the compressor plug.

 

[TurboTdr3.8]

If the wires are getting hot while jumping the pressure switch, there is power present with a high resistance. I would check the diode at the compressor plug.

I have unplugged the wire at the compressor that has the diode in it and it still keeps the jumper wire on the low pressure switch still very hot . So if the diode is bad would that keep power going on through the wiring back to a grd somewhere ? What does the diode do for the system do anyway ?

 

[GNVenom]

A shorted diode will blow a fuse. An open diode will sometimes cause the engine to stumble when the compressor kicks off, due to a voltage spike on the circuit.

Most likely you have a bad fan control relay, probably the low speed relay. http://www.installationinstructions.com/FYI/relaylocations.pdf
http://www.installationinstructions.com/FYI/relaylocations.pdf

 

[krom]

Check the wires in the harness running to the compressor near the drivers header, a friend recently found melted wires causing A/C compressor issues.

 

[TurboTdr3.8]

A shorted diode will blow a fuse. An open diode will sometimes cause the engine to stumble when the compressor kicks off, due to a voltage spike on the circuit.

Most likely you have a bad fan control relay, probably the low speed relay.
http://www.installationinstructions.com/FYI/relaylocations.pdf

My fan works OK on the low side of coming on for the radiator. The green wire going into the relay does it work another relay points inside for the ac ? plus my fuse has not blown for the ac

 

[GNVenom]

The green wire is a control wire from the ECM. The only way that wire will overheat and not blow a fuse would be due to a partial short. A partially shorted relay coil could cause that and still close the contacts. The relay coil is fused on the high side (brown wire) and the ECM (and the AC line pressure switch) provides a ground to energize the relay.

Try swapping the high with the low relay connectors and check for heated wires again.

 

[TurboTdr3.8]

Thanks so much I will try that

 

[87GNSteve]

Well the relay swap fixed my melting wire problem but now after I charged the system the compressor will not engage unless jumped.

 

[TurboTdr3.8]

Well the relay swap fixed my melting wire problem but now after I charged the system the compressor will not engage unless jumped.

Sounds like low pressure switch could be bad , I had one that had 134 switch in it and would not engage the compressor , went bought the R12 low pressure swicth and then it worked