Vastly Changing Suction Pressure
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Joined: Jan 2003
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From: Tucson
Vastly Changing Suction Pressure
Ok, First I am not an Auto AC guy... The vehicle is a 99 Expy with rear AC. If I run the system with only the front on low the suction pressure will drop to 15-20 and the air is below 40f. Now when I put the system on max a/c windows up and rear AC running the suction pressure climbs to 65 and the register air is about 55 degrees. BTW ambient during all this is 90-100 degrees and less than 30 percent humidity. What am I missing, the suction pressure I am seeing should not even be cooling when converted to temperature. Are two evaporators just to much for this system? I am cautious of adding refrigerant with suction pressure at 65 already on max AC. If the system was low wouldn't I see a lower suction pressure until a point where it would start cycling the compressor? And slightly off subject why would these systems use orifices instead of an thermo expansion valve... Is this all about saving a buck or someting unique to auto's that doesn't work well with them?
Thanks,
Dave
Thanks,
Dave
Tuned
Joined: Feb 2003
Posts: 495
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From: Cincinnati, Ohio
Dave,
What is high head pressure when suction is at 65 psi? 15 is low on the suction side and the pressure switch should be causing the compressor to cut out at that pressure. 20 psi on the low side should keep the compressor running in a R-134a system. Check pressures at 1000 rpm windows closed, max AC, both blowers on high and tell us what you are reading. Do you have a shop manual or access to one for that Expy to give you AC performance values? Best bet might be to evacuate the system and pull a vacuum and then recharge to the capacity indicated on the front of the vehicle or at the evaporator case.
John
What is high head pressure when suction is at 65 psi? 15 is low on the suction side and the pressure switch should be causing the compressor to cut out at that pressure. 20 psi on the low side should keep the compressor running in a R-134a system. Check pressures at 1000 rpm windows closed, max AC, both blowers on high and tell us what you are reading. Do you have a shop manual or access to one for that Expy to give you AC performance values? Best bet might be to evacuate the system and pull a vacuum and then recharge to the capacity indicated on the front of the vehicle or at the evaporator case.
John
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Jan 27, 2009 08:28 PM
