M. Mayben, off-brand AC question...

D

DNL

New member
Please forgive this off-topic ac post, but you are the leading ac expert I know, so I hope you can shed some light on this issue for me.
I have a 1996 cadillac sedan deville. Last summer, I foolishly had the ac compressor replaced by morons, and the ac has never worked correctly since.
It is a bone-stock ac system, factory 134a. With gauges on the system, with the ac set to max, the high side pressure ranges from 200 to 300, and it moves a lot. It often switches out the compressor on high pressure. While this is happening, the low side pressure is gradually climbing until it sits at about 25 lbs. When the high side is below 200, the low side gets down below 20 and kicks the comp. Out like it is supposed to, but after the car runs for any length of time, the high side pressure climbs, and starts to kick out the compressor.

Any thoughts on what is going on here? Afaik, only the compressor has been changed, nothing else. I have no idea if it is charged correctly amout-wise. Any advise would be appricaited, and I am an IH guy, I have 7 complete trucks at last count, and used to torment Mike with ac questions on the binder bulletin/planet.

Thanks

dave
 
Dave!!! It's about dam time ya showed up here!

The first thing to always do inna sitch like this is have the system refrigerant recovered, then evacuated, and then charged to the proper volume using an accurate dispensing unit.

Most all GM stuff (but not 100%) like you have is a "ccot" system, which means "cycling clutch orifice tube". Those systems were developed and manufactured by the old harrison radiator group of GM which became part of delco which evolved into delphi and we all now (as taxpayers) own a price of the bankrupt delphi operation. Those do not use an expansion valve, but rather have a plastic orifice tube located in the plumbing loop to create the pressure drop of the refrigerant before it enters the evaporator. They also use an "accumulator" for the system instead of a receiver/drier like ya prolly have on some of your binders.

The orifice tube is problematic regarding clogging since it also serves as a filter. But that condition is not indicated in your description. Orifice tube replacement is somewhat of a "maintenance" thing whenever the system plumbing is opened up for service.

If this rig was in my shop, I would do the "evac and charge" process first, and then run a performance test. Correct charge volume on these systems is imperative, they are not forgiving of charge volume at all. There should be an underhood decal on the car still (hopefully) that shows the type of oil that is oem in the compressor, the type of refrigerant used (r-134a), and the correct charge volume for that actual model vehicle and it's not a "generic" callout, it needs to be exact! The equipment mandated to be used in hvac shops is extremely accurate if operated properly in a charging procedure, no way a r-134a system can be charged or serviced by dispensing "one can" or "three cans" of refrigerant, they must be correct in charge volume by +/- 10 grams.

If...the evac and charge does not correct the condition, then we'll do some further analysis, but the recharge process is always the first thing to do in diagnostics (after doing a gauge diagnostic and performance test), that is not throwing darts, but the standard procedure done today with these advanced design systems.

You keep on comin' around here, we need your participation!!!
 
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Thanks micheal,

ok, everything so far has been sort of fly-by-night, but that ends now. Sticker says 32 oz. 134a, and pag oil. I will get the system pulled down and recharged with that exact amount, and we will go from there.

This system does have an orifice tube, and amazingly enough, especially since it is a cadillac, it is really easy to get to, and very cheap to replace.

Give me a few days to get everything done, and I will report back.

Dave
 
Your are correct dave, orifice tube/accumulator systems use a significantly greater quantity of refrigerant (relatively speaking) than a txv system (thermostatic expansion valve).

My bet...your system currently will be found to be overcharged by about 8oz. Of 134a let's see how close I can guess!!??
 
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