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1990 GM Sierra Compressor Question

extramile on Mon May 18, 2009 11:05 AM User is offline

Year: 1990
Make: GMC
Model: Sierra
Engine Size: 305
Refrigerant Type: R-12
Country of Origin: Canada


Pressurized my system with nitrogen to find the leak and of course is was the O-rings on the back of the compressor, that was the easy part. On the back side of the compressor where the lines attach there is a plug that is broke off, it has a small tube sticking out of the compressor. What in the world is this plug for ??? This system has worked fine with this plug being broke off in the past 3 years just wondering now before I charge system system what it does. I believe the compressor is a Harrison, it is not the long size type but the shorter cylinderical type.

Chick on Mon May 18, 2009 11:30 AM User is offlineView users profile

you have an R4 compressor, and it's the pressure switch on the high side you are talking about.. some have two wires, yours has one..

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Chick
Email: Chick

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Freedoms just another word for nothing left to lose

GM Tech on Mon May 18, 2009 12:23 PM User is offline

On a 1990 vintage that is the switch that throws the system into recirc- when you are in next tio highest or highest fan setting, and next to lowest or lowest temp setting, and head pressure rises above 250 psi-- there is a TSB on it to just ground it permanently and forget the switch....which is what I do...I used to get all kinds of complaints that all of a sudden my fan goes into high high fen mode- then it goes down a level- then when in city traffic it goes up a level-- and what it actually is doing is going into recirc which gives folks the impression the fan speed has increased...We commonly called this the GM truck poor man's climate control......

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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......

extramile on Mon May 18, 2009 2:36 PM User is offline

How do I ground it then. The tiny pipe is sticking out of the compressor, forgive my stupidness as I'm sure the answer is simple.

GM Tech on Mon May 18, 2009 4:16 PM User is offline

You ground the wire that used to be attached to it- a single terminal plug in-- forget the switch in the compressor...you may have to hunt a little for that wire- can't remember the color---but it will be the only one not attached to anything- unless someone cut it off....

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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......

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