high side service valve

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high side service valve

Postby johnbkobb » Mon Sep 12, 2016 9:10 pm

1996 Chevy C3500 7.4L 269,000 miles

When I got this truck the AC didn't work. I've put a set of gauges on it and both registered a static pressure of 0 . Pulled vacuum to about -28 hg and that didn't hold either, slowly lost vacuum. System was empty. Pressurized system with compressed air up to 90 psi hoping to find a leak. It didn't happen until I disconnected the red hose from the high side. I could hear the air escaping from the high side service valve. I knew I'd need to replace it so I got out a Schrader valve remover. Since the valve is vertical I couldn't see the Schrader inside. Pushed down on the tool and began to try loosening the Schrader. Couldn't get it out!!! Climbed on the front bumper to see what was wrong and found that there was no schrader valve in this service valve. Not sure whether it is a ball with a spring or what. Compressor is not seized and the clutch will cycle on and off. Tested it with the vehicle turned on, AC on and an air pressure charge of about 80 psi for about 4 seconds.

Could you enlighten me on this and suggest whether I should replace it with an original type valve or with a Schrader type and why? Thanks for the reply.
EPA 608 & 609 Certified / Burtchville Township, MI / kc8frw at gmail dot com / 1996 Chevy C3500 7.4L Dually 269,000 miles
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Re: high side service valve

Postby GM Tech » Tue Sep 13, 2016 12:28 am

They are replaceable- the top half screws off- this site sells them I believe-- but I am here to tell you that the valve leeking is not your issue- a good plastic cap with a good rubber element (washer) inside will seal off that leaky ball valve- my leak detector confirms that fact many times--

Your issue is, if and only if you have a blue labeled compressor (factory OEM unit), a belly leaker- look and see if you have oily greasy mess around the belly of the compressor- leaks at the head interface to the cylinders are guaranteed if yours is an OEM delphi Ht-6 high mount unit . been there, done that numerous times-- I reseal them- take compressor all apart, clean all sealing surfaces, and put in new o-rings and new shaft seals-all obtained off the Bay....
'95 Chevy 3500 454 Dually 142,000 miles
'94 Chevy Astro Van 358,000 miles!
'86 Buick Park Ave 192,000 miles
'86 GMC S-15 Pick-up 150,000 miles
'92 Chevy Lumina Van - 265,000 miles- given to me to see how far it can go! all above are white!
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