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Ask GM Tech (Cam) Your Own Question
GM Tech (Cam)
GM Tech (Cam), Chevy Technician
Category: Chevy
Satisfied Customers: 15181
Experience:  GM Grand Master Technician 2007. 14 years experience.
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The ac on my 99 chevy pickup wont turn on. The charge is

Customer Question

the ac on my 99 chevy pickup wont turn on. The charge is full and I can cycle the compressor by supplying 12 volts directly to it but when I try to jump the ac relay or the high or low switches nothing.
Submitted: 10 months ago.
Category: Chevy
Expert:  Jared D replied 10 months ago.

Can you tell if you are getting 12 volts at the A6 pin of the compressor clutch relay in the under hood fuse box?

Expert:  Jared D replied 10 months ago.

It should be a dark green wire. Also check for 12 volts at the 10 amp "A/C Comp" fuse.

Customer: replied 10 months ago.
I will check and get back thanks
Customer: replied 10 months ago.
I have 12 volts at both
Customer: replied 10 months ago.
Posted by JustAnswer at customer's request) Hello. I would like to request the following Expert Service(s) from you: Live Phone Call. Let me know if you need more information, or send me the service offer(s) so we can proceed.
Expert:  Jared D replied 10 months ago.

Sorry, we're really swamped here at the shop and I'm not available for a phone call. Here is the diagram I'm looking at for this one:

You should have a diode in line with the AC clutch circuit. If you have 12 volts at the fuse and the dark green wire that leads to the clutch then either the diode is bad or the dark green wire leading to the ac clutch is broken somewhere.

Expert:  Jared D replied 10 months ago.

Also, the ground at the black wire of the ac clutch should be good as well. You don't have 12 volts at the dark green on the compressor do you?

Customer: replied 10 months ago.
where would the diode be located?
Customer: replied 10 months ago.
is the diode going out common?
Expert:  Jared D replied 10 months ago.

No, it's not common to go out; that's why I would check for 12volts at the green wire at the compressor clutch first. The diode is part of the engine harness, approximately 20 cm (8 in) from the A/C compressor clutch connector-according to GM.

Customer: replied 10 months ago.
No voltage at compressor green
Customer: replied 10 months ago.
Found the diode in a small plastic connection how do I test that?
Customer: replied 10 months ago.
No frayed wires this is a well cared for truck
Expert:  Jared D replied 10 months ago.

The dark green side should have 12volts. The black side should have ground. Then test across the diode with your meter set to resistance (ohms) and you should see OL with the leads hooked up in one direction and 1000 to 10 mega Ohms in the other direction.

Customer: replied 10 months ago.
I have 12volts at ac relay but nothing at green ac wire anywhere even coming out of fuse center unnderhood
Expert:  Jared D replied 10 months ago.

Can you check for 12 volts at the IGN E fuse?

Expert:  Jared D replied 10 months ago.

So you have 12 volts at B6 of the relay (dark green with white stripe wire)?

Customer: replied 10 months ago.
Expert:  Jared D replied 10 months ago.

Nothing at A4 (pink wire)- with the relay plugged in?

Customer: replied 10 months ago.
that goes to Inge fuse have 12 there
Expert:  Jared D replied 10 months ago.

Ok. That's good. 12 volts on the orange wire coming from the AC fuse right?