A/C compressor will not come on unless relay is jumped

Jason123177 · 2019-07-19T05:09:27+00:00

I changed the front and rear expansion valves. When I went to recharge the system, after pulling and making sure the system held a vacuum of 30in/hg of course, it would not take a full can of refrigerant. I discovered that the compressor clutch wasn’t engaging. I know I’m not supposed to do this, but I jumped pins 30 and 87 on the clutch relay, and the compressor ran and sucked in refrigerant like there was no tomorrow. After putting the recommended 2.2lbs of R134a, I was getting readings of 205 psi on the high side and 48-50 on the low side but, the clutch still would not engage unless the relay was jumped. This led me to believe that either the control module or pressure transducer was bad. I got a control module out of a wrecked vehicle instead of forking out over $400.00 on a new one. Installed it, reset the PCM and tried the A/C again. Nothing changed at all. I installed a new pressure transducer yesterday, reset the PCM, and again, nothing changed. I did notice that there is a connector in between the condenser coil and grill that isn’t connected to anything. Could this be for an ambient temperature sensor, and could that be the cause of the compressor clutch not engaging? If not, what in the world is going on, because I am baffled at this point.

2008 CHEVROLET UPLANDER

247,000 MILES • 3.9L • V6 • 2WD • AUTOMATIC

ASEMASTER6371

✓Experienced Mechanic
52,796 POSTS

20 lbs on the low side is the pressure needed to turn on the compressor.

25 to 30 lbs is the number for low side. You need an expansion valve.

The electrical issue is separate

Roy

Jul 25, 2019 at 10:23 PM

JASON123177

MEMBER
27 POSTS

The very first thing I done in this process was to change both the front and rear expansion valves.

Jul 25, 2019 at 10:28 PM

ASEMASTER6371

✓Experienced Mechanic
52,796 POSTS

I saw that but the pressure indicates it is not working correctly.

Roy

Jul 25, 2019 at 10:37 PM

ASEMASTER6371

✓Experienced Mechanic
52,796 POSTS

What are the pressures withe the engine off

Roy

Jul 25, 2019 at 10:37 PM

JASON123177

MEMBER
27 POSTS

I will check the pressures when I get home this afternoon and let you know. Thank you again for all of your help!! It is very very appreciated!!!

Jul 25, 2019 at 10:41 PM

ASEMASTER6371

✓Experienced Mechanic
52,796 POSTS

You are welcome

Always glad to help

Roy

Jul 25, 2019 at 10:52 PM

ASEMASTER6371

✓Experienced Mechanic
52,796 POSTS

You are welcome

Roy

Jul 25, 2019 at 10:54 PM

JASON123177

MEMBER
27 POSTS

The static pressure on both sides is 100psi

Jul 26, 2019 at 7:55 AM

ASEMASTER6371

✓Experienced Mechanic
52,796 POSTS

There is something wrong with that front expansion valve.

Roy

Jul 27, 2019 at 4:11 AM

JASON123177

MEMBER
27 POSTS

That’s just wonderful.

Jul 27, 2019 at 5:08 AM

ASEMASTER6371

✓Experienced Mechanic
52,796 POSTS

Sorry to tell you that but the pressure indicates that.

Roy

Jul 27, 2019 at 5:13 AM

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A/C compressor will not come on unless relay is jumped

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