My '08 has been having what used to be intermittent problems with the AC, but is now a constant problem. It behaves more or less like this:

On a cold start, the AC works fine for about 10 minutes. The compressor (which was replaced about a year ago) works fine, and it's nice and cool, cycling on and off normally.

After about 10 minutes, the compressor starts coming on less often, and for less time. After another few minutes, you can hear that it's coming on, then shutting right off again after a few seconds... and then a shorter and shorter time, until it's just clicking on and right off again. At this point, you give up, shut it off, and open the windows.

After a hot start (when you didn't turn it on at cold start), it will work for even less time -- basically not worth bothering with at all, except that I've been running it so I could observe its behavior.

I am not going to try to fix this myself, but as with any problem, the more you can tell the guy, when you take it to a shop, the better off your are. Has anyone had this behavior?

The other thing is that for a long time (say, a couple of years or more), it would misbehave once in awhile -- usually, when wet. Most of the time, though, this was a different behavior -- the compressor would suddenly come on, and start cycling on and off as if the AC had been turned on, when you hadn't turned anything on at all! No defroster, no fan, AC switch not pushed in. This led me to suspect some kind of wiring/insulation issue (especially because i usually happened only when it was raining or wet). But when it dried off, it would go back to normal, so I never bothered to do anything about it.

Thoughts? Culprits?

Urb

 

The a/c system is ECU controlled; grounding the signal wire via switch tells computer to energize a/c clutch and turn on fans. Any short from this wire to the ground acts like a/c switch
The above mentioned wire passes through the series of NORMALLY CLOSED safety switches (min/max pressure switch, compressor body temperature breaker switch); if any of these switches opens up for whatever reason the a/c shuts off
If one of the fans fails to run the gas will not condense and a/c will turn off
If air and moisture is present in the system due to sloppy evacuating/charging the expansion valve will freeze causing a/c system shutdown
I listed here only few common possibilities...

 

That's interesting; a number of possible suspects. Which one would be most likely to account for the fact that the system tends to work fine for a few minutes after a cold start?

 

Radiator fan(s) perhaps?