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The compressor is coming on b/c the relay is closing. Either the relay is bad or something is telling the relay to close. As far as I know, the ACC unit tells the relay when to turn the compressor on. Other things can turn the compressor off, but I think the ACC is the only thing that can tell the compressor to turn on. The ACC will engage the compressor for a multitude of reasons, including defrost. Accordingly, it is not inconceivable that the ACC would run the compressor on HI if it determines defrosting is required.
That said, I can think of only 2 reasons the compressor would run all the time in normal operation. First, there is an undercharge of refrigerant and the compressor is working overtime to try to keep up with the demand. Second, it is really hot out and the windows are down.
If this investigation started due to a lack of cold air, I would investigate either an undercharge or an air mixture problem. If you don't have AC gauges, you can still check the air mixture operation yourself.
If the compressor clutch is engaging, there should be at least some refrigerant in the system. You may wish to eliminate the possibility of an air blend problem before taking the car to have the ac charge checked. First thing to do is to run a calibration of the ACC unit by pushing the Auto and <-> (bottom right) buttons at the same time. If the self test comes up with 0, either the ACC is fine, or it's really broken. Next check that the wire which controls the air mixture flap by the blower motor is still attahced. Turn the ACC to HI and then to LO and make sure that the flap arm moves all the way. If that looks ok, I doubt you have an air blend problem. One last test is to set the ACC on LO and squeeze one of the heater core hoses closed by using 2 small blocks of wood and a pair of vice-grips. If closing one of those hoses makes a big difference in cooling, then you have a mechanical problem in the air mixture area.
One last ACC related thing I would consider is a bad cabin air flow sensor. That's the thing behing the bullseye below the seat heater switches. A bad sensor will cause the ACC to do unsual things. You can try unplugging that sensor and turning the ACC to LO and then to HI and see what happens.
posted by 24.50.58...
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