What pressure for 134a?

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Old 10-13-04, 09:14 AM
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What pressure for 134a?

Can someone kindly tell me the right pressure range for HIGH and LOW sides for R134a at idling speed (say 800 rpm)? My car is 98 Plymouth Breese, 2.0 L. The evaporator seems to freeze up. Initially fine cooling. After a few minutes fog is coming out with noticeably less cooling.

I am trying to figure out if the freezing is from lack of freon or some other problems. I don't smell coolant in the fog.

Right now I am reading about 30 psi (R12 gauge reading) at the suction side at idling rpm. Is this too low? Thanks.

One more question. I maintain my home (R22) and car (R134a) AC's with 1 gauge/hose set. The hose gets released of trapped refrigerant. But oils and dyes stay in the hose set. Do pros recommend separate sets? Thanks.
 
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Old 10-13-04, 07:32 PM
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30 PSI would be high enough that it shouldn't freeze. Have you checked the pressures at the time your having the problem? You could have a restriction in the evaporator that could cause that, among other things.
 
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Old 10-14-04, 08:48 AM
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To answer your other question...

One more question. I maintain my home (R22) and car (R134a) AC's with 1 gauge/hose set. The hose gets released of trapped refrigerant. But oils and dyes stay in the hose set. Do pros recommend separate sets? Thanks.


Yes, most pros will have one set for R-12 and another for R-134. The main reason is compatablility. R-12 and R-134 use different oils and they shouldn't be mixed. Having said that, I don't think using the same gauges once in a while will hurt anything. Another reason may be operating pressures, I know that R-134 tends to operate at higher pressures than R-12, as long as your guages are rated for the systems pressures, you should be good to go.
 
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Old 10-14-04, 09:57 AM
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OK, then the next question is "how are you using a R134 coupler on an R22 fitting"? Are you swapping hoses or something? They definately don't use the same fittings.
 
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Old 10-14-04, 12:09 PM
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I got mixed up. I am using 2 different hose sets. I am just using the same gauge. My apology.

Thanks for the tip. If the evaporator is blocked, should I get a higher than normal reading on the HIGH side? Like 300 psi? Will the safety switch kick in around that pressure? By the way, the AC was repaired twice at a dealer. First time, it was the compressor. Second time, evaporator was blocked. I don't remember exactly what they did second time. I need to know what's going on before taking it back to the dealer again. Whan a compressor goes bad, does it generate particles that can clog the small orifice before evaporator? If it does, how can all the particles be removed without replacing the entire system?

Many thanks for your help. I would like to get the system fixed once and for all.
 
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Old 10-15-04, 02:14 AM
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I don't even know if that is an oriface tube type system. Doesn't it use an expansion valve? Yes, you can get debri all through the system and it can be very difficult to get it all out. It could be lodged in the condenser and releasing a little at a time, depending what type of condenser you have. It's not really something we're going to be able to tell over the Internet. No, you high side woulsn't necessarily go high with an evaporator restriction. You really need a professional to examine it to determine the problem.
 
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Old 10-15-04, 05:24 AM
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Thank you so much for advice. I have not been able to receive professional help at any other online car forum. This weekend I will check pressure and report back. Thanks again.
 
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