Automotive Air Conditioning Information Forum (Archives)

DCdH on Wed July 08, 2015 4:59 PM

Year: 2000
Make: Silverado 2500
Model: 4x4 Short box Ext-Cab
Engine Size: 6.0
Refrigerant Type: 134a
Ambient Temp: 75
Pressure Low: 20-50
Pressure High: 75-50
Country of Origin: United States

I had my truck worked on a few weeks back. The mechanic charged up the AC as well as other items. A few days later it was blowing warm air.

I just bought a set of Gauges and hoses so that I can do some of my own AC work on vehicles as well as farm equipment. My Son was helping and put the new gauges on the AC system. At first it was showing it took him a few times to get the clamps on so he lost a bit of pressure on the high side and once on the low. The gauges showed about 3 psi on both hi and low.

Started the engine and it didn't change so we went to add a can of 134a (12oz). Almost immediately the gauges jumped up and it seemed like the compressor was kicking in. I then verified the valves were set right and my son actually had BOTH the high and low side hoses open (I quickly closed down the high side).

What the system did then was kick in and out (had the AC on and blowers on high).

You'd see the low side gauge go from a low of 20 and go up to 50 while the hi would go from a range of 50-75 and it didn't take that long for this process to happen. I'd expect the compressor to be on for a while since it was warm but it was kicking in and out. When we shut off the engine it showed 50 on both gauges and was steady like that until we disconnected.

I did NOT get any cooler air on from the system.

Dougflas on Wed July 08, 2015 5:13 PM

This website sells a book on AC operation and repair. It would be a great investment to the both of you.

mk378 on Wed July 08, 2015 5:40 PM

Whenever you find a system leaked down to zero it is essential to find the leak first. If you just charge it is just going to leak out again in a few days.

GM Tech on Wed July 08, 2015 6:06 PM

So if you have a flat tire- you meerly put air in it and call it fixed? Find your leak- the compressor will cycle on low refrigerant charge- if you put in the factory specified amount, the compressor will run continuously (to be on for awhile as you stated).

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The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

SlickRidez on Mon July 13, 2015 10:19 PM

I really like that flat tire analogy. Well put!