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George H.
George H., ASE Certified Technician
Category: Chevy
Satisfied Customers: 18490
Experience:  GM Tech ASE Master Tech 15+ years
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Chevrolet Chevy: 02 blazer 4.3, no a/c engagement, low pressure

Customer Question

02 blazer 4.3, no a/c engagement, low pressure switch has ground on both sides and high pressure switch has voltage on green wire and shows around 1 volt on green/white wire. I can jump at relay and engage ac clutch. Would the problem be the high pressure switch on the compressor?
Submitted: 1 year ago.
Category: Chevy
Expert:  George H. replied 1 year ago.
Hello I will help you with your question, If you jumper the low pressure connection and leave the high pressure plugged in does the compressor run? If you jumper the high and leave the low plugged in does the compressor run? Let me know how I can help Thank you
Customer: replied 1 year ago.
Sorry but do u mean give the low switch 12 volts? With engine running and a/c turned to max the low switch is plugged in and shows ground on both sides. I didn't try jumping it because it showed the same thing on both wires while plugged in. Should it be voltage on one side?
Customer: replied 1 year ago.
Everything I checked was plugged in and KOER
Expert:  George H. replied 1 year ago.
Just use a small paperclip to connect the pins of the sensor connector.
The low side is just a ground signal.
Let me know what happens and what questions you have
Thank you
Customer: replied 1 year ago.
OK I'll have to get back with u tomorrow. Thanks
Expert:  George H. replied 1 year ago.
Great, post back to this thread and let me know what you find
Thank you
Customer: replied 1 year ago.
No it still didn't engage the clutch when I jumped the low switch wires.
Expert:  George H. replied 1 year ago.
Not with the low or the high bypassed? Do you have 12 volts at the compressor connector?
Customer: replied 1 year ago.
The system has plenty of pressure and like I said I have voltage on light blue wire at the high pressure switch on the back of compressor but the green and white wire on the same switch shows 1.0 volts. When I jump the high press switch it doesn't do anything either. At the clutch connector I have ground but there is no voltage.
Expert:  George H. replied 1 year ago.
Then we need to go to the compressor relay and jumper between the #30 and the #87 pin socket. IT is marked on the relay. Use a paperclip and if the compressor clutch does not pull in with the key on check the paperclip for 12 volts and the clutch connector. Let me know what happens with that
Customer: replied 1 year ago.
Yes that will engage the clutch. I have tried a new relay also but it did no good.
Expert:  George H. replied 1 year ago.
OK, we know the relay can engage it now we need to know why the computer is not turning it on.
Do you have a check engine light on or signs of overheating?
Do you have a scantool that shows engine computer data?
Customer: replied 1 year ago.
No check engine light and no overheating. No I don't have a scanner to check data.
Expert:  George H. replied 1 year ago.
OK, you can do this with your meter, bypass both sensors with paperclips. Insulate the high pressure one so it does not short.When you turn the switch on for AC it applies the 12 volts to the high pressure switch and if it is closed that goes to the computer as an "AC Request". If everything else is ok (overheating etc) the computer turns on the compressor relay and the compressor runs. The low pressure sensor closes when pressure is above 20 psi and the computer is happy if you bypass its connection to ground. Meet those conditions and the computer should apply ground to one pin of the relay and the relay turns on. What part of the puzzle are you missing? I can help with locations but let me know what happens when you have the sensors bypassed. I know you did this before but it is not adding up what you see happening. Thanks
Customer: replied 1 year ago.
OK I have to get to work, but I'll check tomorrow and let you know what I find. Thanks for the help George!
Expert:  George H. replied 1 year ago.
OK, I plan on being here most of the day so let me know how I can help.
Thank you