Air conditioning problem

[Makaha]

I own a 2001 Volvo Station Wagon V-70 24T and I'm having problems with the air conditioning.

After driving for 25 to 30 minutes the cold air starts getting warmer to the point I have to shut it off and open the windows. The fan also appears to weaken. (Note: I am not using the 'Auto' function).

Through hit or miss experimentation I've found that if I leave it off for 15 or more minutes and turn the system back on, it works fine for 25 minutes and then the warming starts all over.

I've made sure that the system is fully charged.

I have taken it to two shops and in each case they've checked out the obvious (?) and let it run [idle] for up to three hours and the air has, so they say, stayed cold.

This said, it appears to me that in order for the malfunction to manifest its self the car has to be driven at highway speed.

Whats wrong and how can it be fixed?

[jimmy57]

That car has a two wire temp probe that sticks into evaporator case just above and to the right of the accel pedal. Accessible with underdash panel removed. The sensor feeds temp info to the climate control module and the CCM cycles compressor off to prevent freezing. If the sensor is full of fuzz or is defective then the CCM does not get a cold enough temp signal to trigger it to cut off compressor to allow thawing. Usually the temp reaches 32F or a little below and the CCM cuts off compressor until the temp goes over 40F and then turns compressor back on. It is easy enough to do to try cleaning and if it does it again then get a new one. It is white with a green plastic connector on it. Twist and pull and it will come out. it is 3 or so inches long and the sensor part is in the end in a circular opening. If the shop wanted to find bad temp probe on a hot day they would have to run engine up to 1500 RPM and place a high capacity fan in front of car. You have to simulate the conditions of moving down the road in order for A/C efficiency to be great enough for it to freeze up. The two shops weren't really great at A/C diagnosis or they would have found this. I was an automotive educator and I tried my best to beat driving simulation into the students' heads when looking for A/C problems like this but knowing something and practicing it are not the same thing......

[vltjr]

jimmy57 - While our car isn't suffering with any A/C problems right now (or I should say, yet) that's great information that you posted. Thanks.