Automotive Air Conditioning Information Forum (Archives)

jay3000 on Wed July 04, 2012 1:11 PM

Year: 1972
Make: Buick
Model: GS
Engine Size: 355
Refrigerant Type: R-12
Ambient Temp: 85

R-12 AC system evaporator freezes up after about 30-45 minutes.. I don't know any history on the systen other than when I bought this car all of the AC system had been removed.. I found an entire sysyen in my friends garage still under pressure. It has been completely cleaned out with all of the o-rings replaced.. new oil. and a fresh install of R-12. about 3 years ago. I guess I never drove far enough in the summer to notice that it freezes up..

It's COLD at the center vent, Sometimes smoke and ice crystals blow out. But eventually, lack of air flow becomes a problem.. So I assume the evap is freezing. Any idea of a solution?? It has blown vapor and ice crystals out the center vent since it was charged. It was charged by a very experienced AC tech. But I don't know the high and low side readings are. Most times running the fan on low is plenty cool for cabin temps..

I wonder if the POA valve isn't calibrated for 134A??

Any ideas??

Jay

Dougflas on Wed July 04, 2012 4:19 PM

you need gauges and to give us pressures. Make your rpm 1200 to 1500, disconnect blower motor . Low side should be 30psi. This checks the POA

Leggie on Thu July 05, 2012 4:51 AM

How did cars of that vintage control compressor cycle? My car is 91 and it uses thermistor that tells the compressor to shut off when evaporator gets to 0C.

mk378 on Thu July 05, 2012 7:50 AM

POA systems do not cycle the compressor. The POA valve throttles the refrigerant flow to prevent over-cooling.