Lately I’ve been having Ac problems, the POA valve occasionally will chatter and sound like a bullhorn, while the outlet temps are only as low as 75-80 degrees on a 110 degree day. Putting the gauge set on, I get a low side reading of around 30psi give or take depending on ambient garage temp. High side is a bit low but still in the ballpark. This morning, in trying to determine the problem I put my hand on the line leaving the expansion valve going into the bottom of the evaporator and it was ice cold. That’s good, but the low pressure line leaving the evaporator was warm, that’s bad. but after (downstream)the POA valve the line felt was colder, and the small bleed line from the evaporator to the POA valve was ice cold. Is my assumption correct that the POA valve is bleeding off from the evaporator continually so the evaporator essentially gets partially bypassed? I’m thinking the bleed line continually feeding the POA valve is what’s making the line downstream of the valve colder than where it comes directly out of the evaporator. If it is a bad POA valve, are rebuilts or new ones available? Or has any tried to open one up to repair it? One last question, If I have to open up the system what else should be done as preventive maintenance besides replacing the drier?

 

I have to be a bit careful about commenting without knowing more information. If you're in AZ, it would be good to know the approximate relative humidity when you made the test. I'm sure that my LA humidity is significantly higher than what you usually get. It sounds like your duct discharge temperature is too high especially with low humidity. I'm assuming that the system still has R12, as that's what it came with. The POA should restrict flow somewhere around 29 PSI to avoid icing of the evaporator. Evaporator icing should be less of a problem in your part of the world. It sounds like your low side pressure is close to where it should be, but without the cooling capacity. That warm discharge on the evaporator is in agreement with the warm duct outlet. Check the sight glass to see if you have a solid liquid charge going to the expansion valve. It should be "clear". The small "bleed" line from the evaporator to the POA is intended to recover refrigerant oil which tends to accumulate at the bottom of the evaporator. Since the oil and refrigerant circulate in the system together, there may be a bit of refrigerant also coming through the small line but it probably would not be as a liquid. The POA is not considered to be serviceable, and generally is replaced as a unit IF it is determined to be faulty. Availability may be limited. Assuming that there are no leaks to correct, about the only other thing to check is the compressor oil level. Before dismantling, be sure to check the heater control valve and the function of the air doors. I have seen inoperative water valves and leaking air doors completely destroy the efforts of the A/C system.

 

X2 on the heater core vac operated valve as well as other vac operated valves in the duct system. To test a pilot operated absolute valve check the suction pressure at the valve. If the valve gives an improper gauge reading it may be failing. It can be rebuilt or replaced. Yes it is repairable. A POA Valve will generally fail in the open position, letting high pressure vapor into what should be the low pressure side of the A/C system. If the POA Valve is failing, you'll have little or no cold air coming out the vents when the air condition system is operating and the high side reading will be normal but the low side reading will be high. This is because the failing POA Valve is letting high pressure vapor into the low side of the system, which is not your case. Do you have an internal or external expansion valve? Did you check the strainer on the inlet to the expansion valve? The low side sounds ok so I suspect the POA is ok. What is the high side pressure?
The two well known muscle & classic A/C vendors... Vintage Auto Air & Classic Auto Air will have what ever you need to rebuild or repair your system. If none of his make sense Id give either vendor a shout and explain this to them. A noisy POA can be dirt, rust, low charge or moisture or ?

R12
High Side Readings
(Fahrenheit) Outside Air (Ambient)
Temperature
130-160 60
140-170 65
150-180 70
160-190 75
170-210 80
180-220 85
190-230 90
205-250 95
220-270 100
240-290 105
260-310 110
285-335 115
310-370 120