A/C charge and POA valve

[oledave60]

I put in a new dryer that looks like the old one, but it is for 134a and does not have a sight glass.

 

[twozs]

alot of people say you should use the poa eliminator and go to a fixed orifice cycling system when using 134. Rick Love of Vintage Air told us that the molecules in R-134a are smaller than those of its predecessor, and as such over time may leak from old-style flare fittings, which is why new systems employ O-rings. He also mentioned that the pressure/temperature curve is different between the refrigerants, and with GM products from the Sixties in particular, a temperature cycling switch may be required to replace the POA valve (Pilot Operated Valve-replaced by a Valve In Receiver valve, or VIR, in '73),( actually the vir started in 74) which keeps the evaporator coil from freezing. Also, if an expansion valve is part of the system, a new one recalibrated to work with R-134a will be needed too. Of course Vintage Air manufactures new A/C systems, so their interest lies in replacing rather than retrofitting, but Rick knows many will want to keep the original system and has even retrofitted a few himself in the past

 

[oledave60]

I checked the poa when installing everything and it was opening at 31lbs, I adjusted it to about 26 or 27 lbs. This was per an a/c forum that I found.They also said that 134a systems were required to have a high pressure cut-off.

 

[oledave60]

I have all new hoses and the fitting are o-ring (green). The new expansion valve is marked for 134a.

 

[twozs]

well something is skrewey with the pressures and I'm thinking the poa as the suction line is freezing . as stated most techs agree to eliminate the poa valve in the 134 systems. but what do i know . i replaced every part of my 73 z28s air conditioning system but the 2 coils as they were good and stuck with r 12 and that was in 97 and so far so good 12 years later.

 

[oledave60]

Thanks for all the replys. Maby someone else will offer a solution. I sure don't know the answer. But my next step is to remove the poa valve and check it again. Just a guess, but it seems this is where the blockage is. The valve frosts up right to the seam where the charge port is then it is air temp.

 

[oledave60]

I am really confused. If the flow of the refg is from the condenser to the exp valve to the evapator to the poa valve, why is there no cooling in the evapator yet the line from the poa to the compressor turns to ice as well as the metal fitting on the back of the compressor? help please.

 

[twozs]

maybe your not blowing any air over the evap coil . that would cause it to freeze immediately and be your problem??? check your dampers

 

[twozs]

http://www.hvacwebtech.com/RefrigerantCycle.htm

 

[oledave60]

Here is a picture of it frooze up. I tried to add more refrg and it doesen't seem to take anymore.