Automotive Air Conditioning Information Forum (Archives)

LDA007 on Mon July 08, 2013 9:43 PM

Year: 1995
Make: GMC
Model: Sieraa
Engine Size: 305
Refrigerant Type: 134A
Ambient Temp: 85
Pressure Low: 0
Pressure High: 100
Country of Origin: United States

Vehicle is a 1995 GMC Sierra 1500 w 5.0L RWD



This vicious cycle has been going on for about three years.
1)Freon will leak out. Some times fast ( a week) other times slow (three months)
2) I will vacuum the system to find it hold a vacuum.
3) I will refill according to manual. ( 2 pounds or 2.5 pounds depending on source)
4) The air will blow cold for a month to 6 months or longer then will lose all the freon. The last time it was lost in about a week.

The last time this happened, I did the following:


I have put about an ounce may be more of oil with dye in the system.
I have changed the o-rings on the back of the compressor. I would change more but the system keeps holding vacuum.
I have put a new low pressure switch on it.

Unrelated but I also changed:
fan belt.
EGR Valve
Spark Plugs
Wires
Distributor cap and rotor


Currently, I again hooked it up to a vacuum pump and after removing the pump it again is holding a full vacuum (at least three hours now).
To my surprise, not a trace of dye. I am using an 18" long florescent UV light. May be its not right.


Any help will be greatly appreciated.

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Murphy is faster than I.

GM Tech on Mon July 08, 2013 10:31 PM

If it is the original compressor- an R-4- you can bet it needs a new shaft seal- and it probably has the dreaded shell ..o-rings leaking-- those big o-rings are flatter than a pancake over time

these are the two most common leak points- I always start by resealing and new shaft seal in compressor- then let it go- it solves 95% of leak issues.--

If you take your clutch driver off- you'll see massive grease build up- most Old R-4 compressorsl have this. also, do you oil sling strips on the underside of hood liner? this is a telltale sign the shaft seal is a gonner..


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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......

LDA007 on Mon July 08, 2013 11:23 PM

I closely examined the compressor and you are exactly correct. A super fine mist of dye is all over it. I barely am able to see the dye. I will replace the compressor. Do I need to change the accumulator and orifice tube? The video I watched shows this step to be tricky. The orifice tube got stuck and on my truck, evidently it's behind the head lights.

Thank you very much for your help. I have been working on this problem for a long time.
Now if I can just resolve the issue with my transmission delaying shifting and no codes showing. But that's another show. LOL.

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Murphy is faster than I.

GM Tech on Tue July 09, 2013 8:26 AM

I personally don't replace accumulators or OT for a failure mode of a leak--the accumulator will refuse to let go of the evaporator connection and you will tear it up to replace something that doesn't have to be replaced-- OT will be fine....

Been doing a/c jobs like this for 30 years- never an issue not replaceing the A/Ds-- we ran experiments with no desiccant in A/Ds on sheriffs fleets in Texas-- 3 years with no issues---so with r134a the desiccant is not that important...

let the debate begin...just sayin....

-------------------------
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......

LDA007 on Tue July 09, 2013 1:41 PM

Thanks I may check the OT just out of curiosity but I am going to follow you experiences.

To help in the debate you may have started, it's humid in Texas (I'm in Tennessee). So if a failure was going to happen due to the lack of desiccant, it probably would have happened. I love the "Proof is in the Puddin" examples. Thank you for your help.

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Murphy is faster than I.