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No A/C But the pressure is good

Tiny
CANNON1349
  • MECHANIC
  • 2005 GMC ENVOY
  • 4.2L
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 194,497 MILES
The AC started only blowing cold intermittently a couple of days ago. I hooked my gauge to it and it said it was "low."

Today I hooked the gauge to it and more closely saw that when the compressor kicks on, the pressure gets too low and then it kicks off. So, I hooked it up to my AC machine.

Here is what happened:
- The machine held a vacuum at 30mmHg for about thirty minutes.
- It recovered 2.12 lbs (the car holds 1.87 lbs).
- It charged the system with 1.87lbs.
However, it failed the leak test.

How can it be possible to fail a leak test, stay at 30mmHg, and hold the charge pressure?

Now, problem is still that it will not blow cold. In fact, the fans will not even turn on now, even for heat. I am at a loss with the gauges reading good pressures and there is no air.
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Tuesday, August 14th, 2018 AT 11:29 AM

17 Replies

Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
Good afternoon.

If the machine senses a loss of one inch of vacuum, it will fail the test. Make sure the hoses are good and tight. It may be through the hose.

What is the static pressures with the engine off? Both sides.

What is the pressure when the system kicks on with the engine running?

Roy
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Tuesday, August 14th, 2018 AT 12:17 PM
Tiny
CANNON1349
  • MECHANIC
  • 581 POSTS
Low side sits at 110psi and high side 100 psi with the engine off. When the compressor is on the pressure goes to 45/50 psi I think, but still there is nothing leaking to what I can see.
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Tuesday, August 14th, 2018 AT 12:19 PM
Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
What is the high side pressure when running?

You need to do a leak detection with either a bright LED light or the UV glasses and check the entire system.

Roy
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Tuesday, August 14th, 2018 AT 12:30 PM
Tiny
CANNON1349
  • MECHANIC
  • 581 POSTS
Before hand the drier froze up like a big ball of ice, could the leak be there?

Also, what about the fan not coming on in the cabin?
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Tuesday, August 14th, 2018 AT 12:31 PM
Tiny
ASEMASTER6371
  • MECHANIC
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Again, what is the high side pressure when running?

The freezing on the direr indicates moisture in the system.

I need the pressures to see what or why the fans are not working.

Roy
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Tuesday, August 14th, 2018 AT 12:39 PM
Tiny
CANNON1349
  • MECHANIC
  • 581 POSTS
Cannot get a high side pressure, I have already driven the vehicle out and the machine will be in use for real customers.

Sounds like to me there is a small leak and air got in.
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Tuesday, August 14th, 2018 AT 12:42 PM
Tiny
ASEMASTER6371
  • MECHANIC
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When you can get the machine back and check the pressure, get back to me.

I need that to proceed.

Roy
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Tuesday, August 14th, 2018 AT 12:43 PM
Tiny
CANNON1349
  • MECHANIC
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With the engine on and the compressor cycling this is what happens:

The low side sits at 40 and the high at 135 PSI, when the compressor kicks on the low side gets down to 20 PSI and the high side goes down to 75 PSI.
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Tuesday, August 14th, 2018 AT 6:28 PM
Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
When you hit 20 lbs the low-pressure switch opens and turns off the compressor. Your high side is too low as well.

From those pressures, you are low in Freon. You need to recover all the Freon, evacuate the system and add the correct amount and then check the pressures.

Roy
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Tuesday, August 14th, 2018 AT 6:31 PM
Tiny
CANNON1349
  • MECHANIC
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I already did that today. I did see the high side get to 250 PSI earlier but still the fans did not kick on in the cabin.

And unfortunately the fitting on the drier started to hiss after all of this plugging/unplugging.
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Tuesday, August 14th, 2018 AT 6:41 PM
Tiny
ASEMASTER6371
  • MECHANIC
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The Schraeder valve is leaking. That must be replaced. Replace them both.

Lets get the AC working first before we get to the fan.

Roy
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Tuesday, August 14th, 2018 AT 6:48 PM
Tiny
CANNON1349
  • MECHANIC
  • 581 POSTS
Can I replace the Schrader valve without replacing the entire drier? The thing seemed to hold a charge until I started messing with it.
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Tuesday, August 14th, 2018 AT 6:49 PM
Tiny
ASEMASTER6371
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Yes, the valve is like a tire valve. You can get them at any parts store for a couple of bucks.

Roy
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Tuesday, August 14th, 2018 AT 6:50 PM
Tiny
CANNON1349
  • MECHANIC
  • 581 POSTS
Alright I figured it all out.

I did not have an A/C leak, the problem was the end of the gauge for some reason did not make a tight seal at the low side so it was leaking a little bit as I was checking pressures. Guess it is time for a new set. I used a different gauge and added the Freon needed.

The fans would not work because the blower motor resistor behind the glove box went bad. For this car it has an "updated" version and no part stores had it so I ordered it for $25.00. After installing the new resistor, the fans worked again and it was blowing cold!

With the resistor being bad, can it cause the A/C to blow hot before it goes all together?
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Friday, August 31st, 2018 AT 5:11 AM
Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
Yep. What are the high and low side pressures?
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Friday, August 31st, 2018 AT 5:15 AM
Tiny
CANNON1349
  • MECHANIC
  • 581 POSTS
High side was about 100/110 and low side at 90/40.
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Friday, August 31st, 2018 AT 5:17 AM
Tiny
ASEMASTER6371
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Okay, what is the pressure with the AC on?
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Friday, August 31st, 2018 AT 5:36 AM

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