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??
Check what the first Steve mentioned first. The suction throttling valve could be stuck partially closed. Another possibility is a restriction in the evaporator, which is not as common. Also, you can temper the air by dialing the heat on a little if all these possibilities pan out. That'll take care of it.
Seems to me if you found an ENTIRE SYSTEM UNDER PRESSURE, that it would have the correct POA valve for that style system. Does it have R-12 style fittings, or does it have R-134 style fittings? You said that you added R-12... Also, did you get the sensing bulb in the close enough position?
Sensing bulb is right where it should be and insulated.. And yes if the system had been converted it would have different fittings.. Didn't think about that.. Air flow is good. On this trip I ran the fan on high and medium mostly.. For a good portion smoke came out the center vent and then later in the ride the air was not as cool as things started to freeze up..
Have you checked the refrigerant charge level yet? If it is a stock receiver/dryer, you can pop the little plastic cap and view the window, which should be free of bubbles. Any bubbles (or a lot) means a low charge. It will likely have leaked a little in three years. Did you try tempering with a little bit of heater into the system yet?
Well. The system is full.. And I did try running a little warm air with it but that just made the cold air warmer and not cold enough to cool the car.. I ran by and talked to my GM master tech best friends and the first thing out of his mouth is that the POA valve is stuck.. He said "tap it with a hammer a few times" and see if it will start working again.. So, this weekend I will try that.. If not he said "I have plenty of r-12 if you have to open the system".. Found this on Classic Auto Air's site.. On older cars with a POA Valve type system, the Compressor runs continuously whenever the air conditioning system is operating. The POA Valve prevents the Evaporator from freezing by by-passing excessive system pressure. If you have little or no cold air coming out the vents when the air conditioning system is operating and the high side reading is normal but the low side reading is high, or if your evaporator is freezing, chances are good you have a failing POA Valve.
OK.. Drove it around today with vent temps in the upper 20's to around 30 and it was starting to freeze up.. I pulled up and beat on the POA valve with a hammer and the temps went up to 36 or so and it thawed quickly.. So that is obviously where the problem lies.. Guess we will see if the hammer worked or if I need a new one..
