Quote:
Originally Posted by 70GMCer
With a 134 conversion, would the low be set at 30psi cut out? Also, I didn't think there was a high pressure switch for this year. If I install one, would I wire it in series with the low switch?
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HPCO should be wired in series between the LPCO & the AC clutch.
The refrigerant charge level, orifice size, and the compressor cycling switch are kindof an interesting dance.
If the charge level is too low the evaporator will freeze. If the charge level is too high the compressor will suffer and vent temps will rise. As outdoor ambient temps rise the compressor head pressures rise.
The LPCO or Compressor Cycling Switch needs to cut out at a high enough pressure that the evaporator doesn't completely freeze and yet not short cycle the clutch. If the pressure is too low and the compressor doesn't cycle the evaporator will freeze regardless of charge level.
R134a should be roughly 35°F at 31psi in the evaporator.
I wouldn't set the Cycling Switch any lower til you get some runtime on it and observe vent temps and system pressures at around 85°F ambient outdoor temp on MAX AC and max fan.
Good vent temps should be around 40-45°F.
At the temperatures we're interested in, 20°F-40°F R134a runs @ 2PSI lower pressure than R12.
That adjustment screw is sensitive... One eighth turn counterclockwise lowers the cut out pressure approximately 2 PSI and one quarter turn lowers the cut out pressure approximately 4 PSI.
E38.org refrigerant pressure vs temp table
