Compressor Wont Engage

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tommyjack
Posts: 2
Joined: Tue Oct 01, 2019 5:57 pm

Compressor Wont Engage

Postby tommyjack » Tue Oct 01, 2019 7:47 pm

I have a 2011 Chevy Suburban, 5.3 engine, with rear air, 140k on the clock. Compressor will not engage. I can pull the relay at the box and jump it. Blows cold. Changed out relay with another from the fuse box (same part number, it's for the driving lamps), still wont engage. When engaged/jumped the low pressure is 42 and high is 213. Ambient temp here about 78 degrees. Did NOT blow air through condenser but I did test drive. When issue started, I replaced both OTs, pulled vacuum and recharged with approx. 3lbs per the decal in engine bay, using cans which is why is say approx. Since recharge I have also replaced the inline transducer switch, ambient temp sensor in front of condenser. Any advice here would be greatly appreciated and I promise when its figured out I'll post an answer for the next guy or gal. Thanks
BSTactics
Posts: 3
Joined: Thu Aug 29, 2019 6:55 pm

Re: Compressor Wont Engage

Postby BSTactics » Tue Oct 01, 2019 8:40 pm

Do you have access to a GOOD scan tool? If so, scan it. Check for ac request signal, air intake temperature, & a/c pressure. The expensive (good) scan tools can even override the pcm and turn on the compressor to check for functionality. Even if the system is okay, the pcm won't allow it to operate if those 3 conditions aren't in range.

Without a proper scan tool, it's pretty much a guessing game. If the check engine light is on, then make sure none of the codes correspond to any of those above AND check for continuity between all of the connectors for them as well. Corrosion, rust, broken plug, frayed wiring, ect. will cause mis-readings to the pcm which won't allow the system to operate. Basically everything needs to be perfect or as close as you can get it. Once you know continuity is good between all the sensors and pcm & pcm to bcm, you can move onto checking for your 5v reference signal to all of your sensors (A.i.t., high/lo pressure, map, maf [if equipped), ect.)

Since you've tested the compressor already and determined that everything functions there, your problem has to lie in meeting the right parameters for the pcm in order to turn on the ac. If you don't have access to the right scanner, there is Chinese made gm scanners for around $300 selling on Amazon. Of course they're knock offs but who wants to spend $2k to fix a $10k vechile.. Not me. Esp. when certified master mechanics can't tell the difference on YouTube.

Hopefully this helps you out some. Just let me know.
tommyjack
Posts: 2
Joined: Tue Oct 01, 2019 5:57 pm

Re: Compressor Wont Engage

Postby tommyjack » Wed Oct 02, 2019 4:26 pm

Thanks BSTatics. If I have to i'll bite the bullet and take it to a shop. Heck they gotta eat to right?

HOWEVER... had to drive the Burban today for about 15 minutes. It started cycling on for 10-30 seconds, cool air, then off for anywhere for 20-90 seconds. Could this be a pressure issue?
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Cusser
Posts: 479
Joined: Sun Apr 24, 2016 6:29 am

Re: Compressor Wont Engage

Postby Cusser » Wed Oct 02, 2019 6:56 pm

tommyjack wrote:Thanks BSTatics. If I have to i'll bite the bullet and take it to a shop. Heck they gotta eat to right?

I'd take it (1) to a real auto AC shop if there's one in your area, not a Brake-O or similar who just has a sign. (2) would be an independent ASE mechanic shop.


tommyjack wrote:HOWEVER... had to drive the Burban today for about 15 minutes. It started cycling on for 10-30 seconds, cool air, then off for anywhere for 20-90 seconds. Could this be a pressure issue?

Could be a pressure issue due to insufficient refrigerant. See above response.
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JohnHere
Posts: 171
Joined: Sun May 13, 2018 10:20 am
Location: South Carolina Upstate - USA

Re: Compressor Wont Engage

Postby JohnHere » Fri Oct 04, 2019 3:36 pm

Cusser said: Could be a pressure issue due to insufficient refrigerant. See above response.

+1 on that. It would be very interesting to recover the charge and see how much is in there now. If it's low, the system has a leak someplace.

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