I have a '96 850 Turbo Wagon. Recently I had the a/c evaporator replaced at the dealer.

Now that the weather is a little warmer up in Canada (23 to 27 degrees C) I have had problems with the system freezing up. It seems that during highway driving and low fan speed, the evaporator seems to ice up after about 30 minutes. I believe it is icing up as the air flow becomes significantly reduced (even if the fan is then set manually to full speed) and the air is cool rather than cold. If I turn off the air conditioning, in a few minutes the air flow returns. I have also noticed that I often have a thin layer of ice forming on the line at the firewall between the evaporator and the accumulator. Icing also sometimes occurs at the firewall on the line from the condensor to the evaporator. The a/c clutch on the compressor does cycle on and off when the evaporator is not iced up. The last time the evaporator iced up and air flow was reduced, I believe the compressor was staying on full time (I didn't think to check the compressor the other times the air flow reduced).

Icing should not be a normal situation. Does anyone have suggestions on what might be the root cause (e.g., over or under charging of the system, a faulty low pressure switch,...) ?

Thanks in advance,

Garth Gullekson

1996 Volvo 850 Turbo Wagon
2001 Subaru Outback
1978 Porsche 911 (no A/C !)