AC Questons


Old 07-08-04, 09:29 AM
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AC Questons

96 Firebird 3.8L

Bought the car new and the AC has always been marginal. The dealer checked it out and said it was working as designed. I have verified that the refrigerant operating pressures are in the normal range.

I have noticed the low pressure refrigerant lines are not insulated like the old days (70ís and 80ís). The compressor is beneath the cylinder head and therefore the a portion of the suction line is in very close proximity to the exhaust manifold. Certainly there is substantial heat transfer occurring. I am considering insulating the low pressure lines to reduce the amount of superheating. Is there any reason I should not do this?

In the old days, I recall GM AC compressors cycling on and off during normal operation. I donít see this type of operation on my or other modern cars. How is compressor outlet pressure controlled? Is there a bleed or bypass inside of the compressor? Is the outlet pressure what it is based on engine speed and refrigerant temperature?

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Old 07-08-04, 11:15 AM
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I don't know much about AC, but on my 99 Tahoe the compressor cycles on and off by itself. It does it on all of my cars, but this is the only GM car I own.
Old 07-08-04, 02:17 PM
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What do you consider marginal please describe how you came to that conclusion.Does the car have a sun roof?What are the a/c pressures that you read?Hi side pressure is temp related as is low side pressure.That is part of how heat transfer works.
Old 07-08-04, 03:35 PM
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Stick a digital thermometer into the center vent and drive around on high fan. If you can pull in the low 50s, there's nothing wrong with it. There wouldn't be a lot of point in insulating the suction line because that is the return from the evaporator and has already done it job and it entering the compressor to start the cycle over again.
Your car does use a cycling switch but if your running the blower on high, the pressure will likely stay high enough to prevent cycling. It is programmed to go off around 24PSI and back on at 48PSI. With a full charge and high blower on a hot day, it will likely never see 24PSI.
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