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roybelding
roybelding, Master Tech/Trainer
Category: GMC
Satisfied Customers: 4656
Experience:  35 years of retail operations on all vehicles
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I have a 2004 GMC Sierra 1500 4.8. The a/c compressor will

Customer Question

I have a 2004 GMC Sierra 1500 4.8. The a/c compressor will only engage when relay jumped. no power or ground on spade 85 of the relay
Submitted: 1 month ago.
Category: GMC
Expert:  roybelding replied 1 month ago.

hello, my name is ***** ***** I will be glad to assist you. please allow me a couple of minutes to gather some basic info.

Roy

Customer: replied 1 month ago.
Okay
Expert:  roybelding replied 1 month ago.

ok, attached a wire diagram for you to view

do you have any power to the low pressure switch??

did you verify powers to the ac clutch relay???

Roy

Expert:  roybelding replied 1 month ago.

check ignition fuse E in the fuse box. that powers the control side of the relay which is terminal 85

Customer: replied 1 month ago.
I have power to the spades 30 and 86 on relay. I can jump power to 87 and compressor engages. No power to low pressure switch
Customer: replied 1 month ago.
That fuse is good.
Expert:  roybelding replied 1 month ago.

with the relay plugged in, can you test terminal 85 for power???

Customer: replied 1 month ago.
no power
Expert:  roybelding replied 1 month ago.

ok, are you using a volt meter or test light

Expert:  roybelding replied 1 month ago.

is there freon in the system???

Customer: replied 1 month ago.
Test light
Customer: replied 1 month ago.
Freon is full works when jumped
Expert:  roybelding replied 1 month ago.

ok, good. when you probed the relay with the test light, it should have created a ground, which is what terminal 85 is for. if the relay did not energize, the relay is bad.

can you switch it with another relay???

Roy

Customer: replied 1 month ago.
switched with horn still doesnt work
Expert:  roybelding replied 1 month ago.

with the horn relay in, can you re check terminal 85 with the test light??? the test light should provide a ground and activate the relay

Roy

Expert:  roybelding replied 1 month ago.

are you there

Expert:  roybelding replied 1 month ago.

are we going to continue???