I had the AC evaporator, receiver/drier and expansion valve and recharged with R12 two months ago, and it is acting a bit odd to me.

First of all, after taking the 10 minutes or so to cool down, the temperature at the vent is anywhere from 43-48?F. However, after about a half hour of driving on the freeway, I can watch the dial on the thermometer rise. At which time, the vent temperature was about 65?. Again, this was on freeway driving and ambient was about 85-90.

I do some tile shopping for my leaky shower for an hour and a half, and the system was back down in the 40's after a short drive but then crept back up again. This should rule out low Freon. I should also note the CCU is trying to compensate with a gradually higher fan speed, which leads me to believe it's not the CCU.

Any guesses as to what is going on? Will overcharging the system do this?

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1999 Black MB E300TD - 135k miles
2007 Toyota FJ Cruiser - 2k miles

Maybe the AC is battling a leaky monovalve.

Sixto

this system is equipped with a pressure switch which cuts off the circuit of the ac compressor when the system is under-charged or over-charged. if i will make a guess, the system is over-charged. why did i say so? your ac gets cold then quits after a while which makes me think that the freon gas expands when it gets hot, therefore, expanded gas will build up high pressure and cuts the ac compressor circuit off. check your refrigerant pressure try to relieve the pressure a little bit if you think its too high.

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'85 300D Turbo - CA Version