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Vacuuming the system

torque395 on Sun July 31, 2011 12:09 PM User is offline

Year: 1996
Make: Chevy
Model: Suburban
Engine Size: 6.5L
Refrigerant Type: R134A
Ambient Temp: 90
Country of Origin: United States

When vacuuming the system down do I open both high and low side valves or just one valve?

1996 Chevy Suburban 2500 4x2 6.5L Turbo

70monte on Sun July 31, 2011 1:19 PM User is offline

I always do both sides.


Airstream on Sun July 31, 2011 4:26 PM User is offlineView users profile

Originally posted by: 70monte
I always do both sides.
I would have thought pulling down both sides was best because if you only pull the low side, then that means the air/moisture on the high side has to bleed through the expansion valve/orifice to eventually make its way to the low side.

But I'm new at all of this, and my truck was just found to have way too much oil in the system. A lot of it is was found to be hanging out near the high side fitting [maybe] because the fitting is below the evaporator.

Although the truck now has a more appropriate oil level, I'm leery about pulling on both sides because I don't want to flood my vacuum pump with oil it may not like.

I'm willing to bet this question has been asked before, and the guyz who really know what they are doing are tired of answering the same ole question are tired of responding.

I've now got a different "take" on the question. A new Mastercool vacuum pump was purchased to get my '84 Suburban cooling us again. If it was to suck in PAG150, would it simply blow out the excess & keep pumping down to what it can do, or do I need to stop & change the oil when the sight-glass shows too much oil in the chamber?


GM Tech on Sun July 31, 2011 5:42 PM User is offline

I've never even had that concern--and I've been doing a/c for 25 years....oil will not come out under vacuum-- only when mixxed with liquid refrigerant.....and if it did- your vacuum pump would "process" it and spit it out its harm done...

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......

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