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R12 Low side is high

dschmit on Tue June 29, 2010 11:28 AM User is offlineView users profile

Year: 1970
Make: chevrolet
Model: chevelle
Engine Size: 454
Refrigerant Type: r12
Ambient Temp: 90
Pressure Low: 42
Pressure High: 215
Country of Origin: United States

Factory POA/TVX system with the exception of a Seltec 15HD compressor and a parallel flow condenser. Last charge was two years ago and now most of freon was gone, but the compressor still cycled. Evacd system to 29.5 inches for half an hour and let set to check for leaks, all is good. Charged with 2 lbs 4 oz of R12, sight glass runs clear, at 1500 rpm engine temps @ 220, high pressures 210-215 low stays at 41-42 (doesn't move) cools to 52 vent temps in stall with a fan in front of car. Down the road vent temps will drop to 48-50 and engine temp at 200. I unhooked the blower fan and the low pressure reading does not move from 42, I thought it should drop to around 30 psi. Hows come I do not see lower pressure on the suction side? Is the compressor too small (compared to the A6) for the system, or maybe it has a valve stuck or is bad. Stuck POA? I did not try to put the TVX bulb in ice or warm water to see if that would change things

Chick on Tue June 29, 2010 12:54 PM User is offlineView users profile

It's working correctly, the POA will keep suction pressure steady...thats how it's designed...

Email: Chick


Freedoms just another word for nothing left to lose

Dougflas on Tue June 29, 2010 6:56 PM User is offline

If you disconnect the blower motor with the rpm at 1200 to 1500 and the low side does not drop to 30psi, (provided your gauges are calibrated) the POA is bad. 48º on those systems were the normal.

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