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sprinkles08, ASE Certified Technician
Category: Chevy
Satisfied Customers: 21436
Experience:  ASE Master and Advanced level certified. Factory trained with 15 years dealership experience
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Can't resolve ac issue 08 cobalt, how to check when clutch

Customer Question

can't resolve ac issue 08 cobalt
JA: Have you checked the Freon level? Have you checked the hoses?
Customer: how to check when clutch not engaging
JA: What year is your Cobalt?
Customer: 08
JA: Are you hoping to fix this yourself? What have you tried so far?
Customer: 08 ls
JA: Anything else you think the mechanic should know?
Customer: have replace clutch, high low pressure switch, continuity from relay to clutch, but no power
JA: OK. Got it. I'm sending you to a secure page on JustAnswer so you can place the $5 fully-refundable deposit now. While you're filling out that form, I'll tell the Chevy Mechanic about your situation and then connect you two.
Submitted: 4 months ago.
Category: Chevy
Customer: replied 4 months ago.
continuity to clutch from relay, no power. other fuse good. replaced clutch and high low pressure switch, still no power at clutch
Customer: replied 4 months ago.
on clutch relay 4 pins, one is hot when engine off, 2 are hot when running
Customer: replied 4 months ago.
2 are hot even before ac switched on
Expert:  Juan Crespo replied 4 months ago.

Hi there.

Once the A/C control is turned on, a request is sent to the onboard computer (PCM). The PCM then looks at refrigerant pressures, engine temperature and throttle position. Once it sees all of those parameters are met, it grounds the clutch coil relay and the compressor engages.

So first question is; do you have a scan tool that can communicate with the PCM to see if there is a request signal from the A/C control? Second, have you checked refrigerant levels and pressures? Third, have you checked for 5 volts at the Gray wire connected to the A/C pressure sensor?

Customer: replied 4 months ago.
how to check pressure with compressor not working, use fill gauge?
Customer: replied 4 months ago.
no on gray wire
Expert:  Juan Crespo replied 4 months ago.

There are two kinds of refrigerant pressure; static (compressor not working) and dynamic (compressor working) both can be measured with a manifold gauge set (click here to see example). Static pressure gives us an idea of system charge in relation to ambient temperature; dynamic pressure tells us the state of the system and its components.

The A/C system in your vehicle is controlled by the PCM, which also sends the 5 volt reference signal to the A/C pressure sensor. Without a Tech-II or equivalent scan tool, we can do very little; ad to that not having a set of gauges and we're guessing instead of diagnosing.

If I were to guess, taking into consideration the fact that you post there is no 5 volt reference signal coming from the PCM, I'd say it is bad.

Customer: replied 4 months ago.
no I have not checked 5v wire, thats at pressure sensor, I put pressure valve on low side and it read over 65, bled down to 40
Expert:  Juan Crespo replied 4 months ago.

I’m sorry, but I don’t have any other information that could help you at this time. I’ll opt out so others may try. Please do not reply until another expert responds or the site will cycle this request back to me.

Expert:  sprinkles08 replied 4 months ago.

Hello and welcome to JustAnswer!

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