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AC charge pressure

Tiny
SIERRA GUY
  • MEMBER
  • 1997 GMC SIERRA
  • 105,000 MILES
Truck not blowing as cold as it used to. With air temp 90-95 what is recommended low port pressure? Should read ac. Pressure I am getting with engine running and warm with everything on max is 31 PSI.
Wednesday, July 26th, 2017 AT 7:05 PM

17 Replies

Tiny
HMAC300
  • MECHANIC
  • 48,601 POSTS
Low port pressure depends on condition like wind etc you could be that low but sounds like system needs some juice should be in 40 range.
https://www.2carpros.com/articles/re-charge-an-air-conditioner-system
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Thursday, July 27th, 2017 AT 7:06 AM
Tiny
SIERRA GUY
  • MEMBER
  • 21 POSTS
Everything hooked up engine warm. Ac, fan at max. Gauge reading 31, open valve on can and goes to 80 psi. Immediately shut off valve to can pressure returns to 31. Any ideas other than take to pro?
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Friday, July 28th, 2017 AT 12:54 PM
Tiny
HMAC300
  • MECHANIC
  • 48,601 POSTS
When you add Freon on a hot day or anytime really unless system is empty it will go way up and compressor will compress the gas it will go down some as it takes it in. You should have windows open as well when you add Freon. Then when you shut the valve off to add will give you a reading that is more like what it should be. On that kind of temp you should do at a fast idle like 1500 or so and if outside temp is in 90 degree range a fan in front helps. Check it after about a half can as can will be warm on top cool on bottom. See what you read and what temp is coming out center vent. But if you really don't know what you are doing then a pro should do that. Least that is my opinion.
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Friday, July 28th, 2017 AT 1:16 PM
Tiny
SIERRA GUY
  • MEMBER
  • 21 POSTS
Thanks, will try again. Was afraid I was gonna damage system.
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Friday, July 28th, 2017 AT 1:40 PM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 47,642 POSTS
Please let us know what happens, we are interested to see what it is.

Cheers, Ken
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Saturday, July 29th, 2017 AT 11:38 AM
Tiny
SIERRA GUY
  • MEMBER
  • 21 POSTS
Decided to roll the dice and try again. With temp 95 and someone holding 1500 rpm pressure was 41.I left it alone, figure ac was trying as hard as it could with it being so fricking hot.

Thanks y'all
Never let me down.
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Sunday, July 30th, 2017 AT 6:56 PM
Tiny
HMAC300
  • MECHANIC
  • 48,601 POSTS
When it is that hot you need to put a fan in front of vehicle you could add some more Freon bring it up to 45-47
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Monday, July 31st, 2017 AT 6:09 AM
Tiny
SIERRA GUY
  • MEMBER
  • 21 POSTS
Took it to a pro, 15 minutes and a can of freon, blowing as cold as when it was new. Thanks for all the help.
Tom
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Tuesday, August 1st, 2017 AT 12:17 PM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 47,642 POSTS
Nice work, we are here to help, please use 2CarPros anytime.

Cheers, Ken
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Wednesday, August 2nd, 2017 AT 10:55 AM
Tiny
JOHNNY DILLARD
  • MEMBER
  • 1 POST
  • 1992 GMC SIERRA
  • V8
  • 2WD
  • AUTOMATIC
  • 160,000 MILES
Air Conditioning problem
1992 GMC Sierra V8 Two Wheel Drive Automatic 160000 miles

RECHARGED A/C SYSTEM WITH 134a and flush out and vac down but forgot to install new orfice tube old one has been removed and now ac dosent get cool but working a little do I need the tube installed?
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Wednesday, August 2nd, 2017 AT 10:56 AM (Merged)
Tiny
JIM SHIRRON
  • MECHANIC
  • 77 POSTS
Yes, you do have to have the orifice tube. It is really the "expansion valve" for your A/C system
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Wednesday, August 2nd, 2017 AT 10:56 AM (Merged)
Tiny
JIM SHIRRON
  • MECHANIC
  • 77 POSTS
Also, where are you? I own a r134a recovery/ recharge machine, I would be glad to help if I could.
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Wednesday, August 2nd, 2017 AT 10:56 AM (Merged)
Tiny
BITTERCRITTER
  • MEMBER
  • 2 POSTS
  • 1990 GMC SIERRA
Dad had a stroke. Used to be a master mechanic and a used volvo dealer. I am his 39 year old daughter taking care of him. He bought a 1990 gmc truck and we're working on a/c. I can charge his volvos with his equipment but am not bright enough to figure out how to make that equipment work on this vehicle. The connectors don't match up. All he has is 134A. Dad can scoot around in his chair but he can't talk. Are there adaptors? Advice?
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Wednesday, August 2nd, 2017 AT 10:56 AM (Merged)
Tiny
WRENCHTECH
  • MECHANIC
  • 20,761 POSTS
A 1990 would have come originally with R12 which you can no longer buy. You can retrofit the system to R134A by changing the oil in the system and installing retrofit adapters. I have to warn that this change doesn't work out well with all cars as they were engineered for R12. When recharged, you use only 80% of the original R12 charge.

I would suggest Googling R12 retrofits and read up on the methods and pros and cons.
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Wednesday, August 2nd, 2017 AT 10:56 AM (Merged)
Tiny
BITTERCRITTER
  • MEMBER
  • 2 POSTS
Excellent. You were right, of course. Dad already had the conversion kit and the dealie with the three gauges and all the hoses. And boxes of 134a. But eventually something had to be bypassed for a second with a piece of wire.(Completely beyond my comprehension. Thank jebus for stand-in mechanics when they show up). Mechanic said something about tricking the brain for a second so he could continue. We jacked up the price of the machine by many dollars with your advice. Thank you. I will feel even better when the machine sells.

KC
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Wednesday, August 2nd, 2017 AT 10:56 AM (Merged)
Tiny
JOHNROBE
  • MEMBER
  • 1 POST
  • 1995 GMC SIERRA
Air Conditioning problem
1995 GMC Sierra V8 Two Wheel Drive Automatic 150K miles

AC is loosing Freon. Leak started as a small one - then got worse. System works fine when recharged
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Wednesday, August 2nd, 2017 AT 10:56 AM (Merged)
Tiny
DOCFIXIT
  • MECHANIC
  • 18,828 POSTS
Yo need to have the system leak checked most shops do for small fee that is applied to repair. I think you Evap is problem. If so set down before you read estimate.
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Wednesday, August 2nd, 2017 AT 10:56 AM (Merged)

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