IT freezes up into a chunk of ice all the way back to the compressor ..no cold air by the vents. Does POA actually go bad or is the expansion valve the actual problem? Thanks
It could be low on charge, or may be a plugged orfice screen in the expansion valve. It also could be moisture in the system freezing in the orfice making a restriction, and freezing internally in the POA. When the expansion valve goes bad, usually the result will be insufficient cooling, and higher low side pressure. The expansion valve allows more liquid refrigerant to enter the evaporator as it gets warmer at the outlet pipe. (due to increased load from warm temps inside the passenger compartment) When it gets cooler, less liquid refrigerant is sent in to cool it. A flooded evaporator will actually cool less, b/c it needs to boil down to a gas by the time it exits the evaporator. When liquid refrigerant boils, it removes heat. Too much will not boil and therefore not remove heat. The POA responds to the change in pressures resulting from more or less liquid refrigerant entering the evaporator, (and engine RPM) so that the low side stays above 28 lbs, keeping the temp above 32 so it won't freeze over. In your case, the evaporator pressure may be going way too low and it's temp. is getting below freezing, which is making the ice. I hope I didn't confuse you.
Joe is right :Smarty: What refrigerant are you using? Although it could be other things, what you described sounds like a bad POA valve. They can be tested on or off the car but if you do it on the car you need to be sure the refrigerant charge is right. That means weighing it in. IF you're going to weigh in the charge you're going to have to remove what's in there. If you're going to do that I'd rather just bench test it. The cost of refrigerant makes things more complicated. TESTING THE POA ON THE CAR... "The Pilot Operated Absolute Suction Throttling Valve-POA for short- mounted at the evaporator outlet is a back pressure valve that will close when the evap starts to freeze, raising pressure and therefore temp to above freezing. The way to test this is- hook a lo press gauge to both access port on POA and the access port closer to the compressor. If you don't have two, use the high side gauge on the port closer to the compressor. Run AC system, disconnect blower motor, run at approx 1200-1500 rpm. Gauge on valve should stay in 28-32 range, you should see it move up and down, you might even see the hoses frost a little, then thaw. Gauge closer to compressor can drop down to, but not go below 0, if it gets that low you will see the equalizer tube- small tube comming out of bottom of evap or out of xvalve going to POA-frost up when compressor port is at 0. Sometimes, doing this will make a sticky xvalve or POA unstick. Don't forget to reconnect blower motor, don't do this for more than 5 minutes, stop if the compressor gets noisy, because at 0 at the compressor port, you are returning liquid to the compressor."
After 2 junk yard POA 's the third one worked ! I cut the suckers open and they were both rusted shut they looked clean from peeping down the holes .I bench tested them by passing high pressure air into the inlet end and you could hear/feel the valve poping open the rusted one's did nothing.
I had one from a junkyard once that appeared to be clean as a whistle on the inside, and the outside was even nice too. My a/c worked fine, all the pressures were OK but everytime I decelerated with the a/c on the thing would make a sound like a bullhorn for a few seconds. I never had one do that before! ou: I never bothered to cut it open but perhaps I should have.
Are you sure you didn't run over a moose? Being the big fan of the POA valve that you are, I'm surprised you had never heard that before. It used to happen quite often when there were a lot of those cars on the road. I never bothered to open one up either, but someone told me once that a spring inside would break and let the valve flutter causing the noise.o No:
