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Failing to charge

beginner on Fri August 17, 2012 9:26 PM User is offline

Year: 1991
Make: chevy
Model: silverado
Engine Size: 350/5.7
Refrigerant Type: R-134
Ambient Temp: 102f
Pressure Low: 120
Pressure High: 0
Country of Origin: United States

I bought this truck with a non functioning AC system that was retrofitted with R-134 . I replaced the accumulator and pulled the proper vacuum 3 times . I got 3/4 of a 12oz can of refrigerant into the system , but the compressor will not start even with 120 pounds on the low side . I jumped the low pressure switch and the compressor runs , but it runs like it is free wheeling . There is no pressure change on the low or high side with the compressor running .

(1) how long can I run the compressor under those conditions for testing ?

(2) Is the compressor most likely bad or is there another possibility ?

Thanks for any help .


Edited: Fri August 17, 2012 at 11:14 PM by beginner

mk378 on Fri August 17, 2012 9:52 PM User is offline

Something is wrong with your gauge hookup, high side and low side should be the same with compressor off.

Switch is likely bad. It should close at pressure above 50 psi. Make sure it is fully seated to the accumulator-- but hand tight only.

Inspect the OT for debris to get some idea if the compressor has blown up. The R4 should be difficult / impossible to turn by hand even when good.

Don't jump the switch to charge. You should be able to dump in one or two cans as liquid with the engine off. Then the switch will be closed and you can engage normal operation and complete the charge as vapor.

Nobody has had very good results trying to convert those particular trucks.

Edited: Sat August 18, 2012 at 1:49 PM by mk378

beginner on Tue August 21, 2012 6:03 PM User is offline

Thanks for the reply .

I borrowed another gauge set , but still the same problem . After some gauge troubleshooting , I found that the R134 quick connect couplers on both gauge sets would not open the shrader valves enough for the valves to work . If the couplers ( on both sets ) are manually held in the maximum bottomed out position , the shrader valves open enough to work . If the quick couplers are put on the normal way , they do not work or sometimes work . I went down and bought new R134 fittings and new shrader valves , but its still the same .

I don't understand why the stack tolerance is off . Do I need to get a special shrader valve with a longer than normal stem ? ... totally confused here .

Thanks .


Edited: Tue August 21, 2012 at 6:03 PM by beginner

bohica2xo on Tue August 21, 2012 9:31 PM User is offline

Obviously it is a vehicle problem if more than one coupler does it.

I just use a zip tie around the assembly to hold it open when this happens. Seems like GM had some sloppy tolerances in that area, seen it more than once.

oops. Just re-read your last post. Conversion fittings. If you are using the ones that keep the original schrader, they are know for this problem too. Buy quality fittings with their own schrader,and toss the OEM schrader valves.


"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

Edited: Tue August 21, 2012 at 9:34 PM by bohica2xo

mk378 on Tue August 21, 2012 10:08 PM User is offline

You probably also have the special GM "deep throat" on the original R-12 high side where the shrader is recessed. That shrader must be removed and a converter with its own shrader installed.

Use these converters or similar (from the site sponsor or found at better local parts stores). They are steel with a yellow finish. The aluminum conversion fittings on the market are junk.

When you're starting with an empty system that needs to be evacuated, here's one way to tell if your hoses are properly coupled. Open only the high side at first to start to evacuate. You should see the low side gauge go down into vacuum if you're really evacuating everything. Having confirmed that, next open the low side too and let it pump out both in order to get a full vacuum.

Edited: Wed August 22, 2012 at 10:59 AM by mk378

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