Recently, the A/C compressor on my '08 has started coming on whenever I turn on the heater fan. Normally, it's supposed to only come on when you're using the defroster, but now, it comes on regardless of the heater position (floor, floor/dash, floor/defroster, defroster alone).

Several months ago, I noticed it coming on whenever I turned on the fan -- the headlights dim noticeably for an instant when the compressor comes on, then the voltage regulator responds and they brighten again. OK, so I noticed that it was coming on. That was in a heavy rainstorm, and it was coming on even when the fan was turned off entirely -- so I thought maybe there was a short caused by moisture, because when the car was dry, it wouldn't do it. But from time to time, the problem has occurred -- sometimes when the car's wet, sometimes not. And for the past week or so, it happens all the time -- whenever I turn on the fan, the compressor comes on. I have not had a recurrence of having the compressor come on even when the fan was turned off.

What's the likely cause of this problem? (It's probably irrelevant, but I think I need a new compressor anyway -- the A/C stopped working suddenly last summer, but I was in the middle of moving and didn't have time to drop my car off and not have it for a few days. Since it's running OK otherwise, I got lazy and haven't fixed the problem yet. I don't think it's just leaking refrigerant, because it's a little noisy, besides just not working.)

Urb
'08 Fit Sport
5-speed
More fun than the Corvette I used to drive

 

So, when you are turning your blower motor, the a/c kicks in?
Are the engine cooling fans on when a/c is on?

 

Is the AC pushbutton switch stuck in/on?

 

Will check the cooling fans next time I'm out there (I have to park in a municipal lot down the street). I don't think the A/C switch is stuck in, but will make sure, for idiot-elimination purposes.

One reason I asked was to find out if there might be a non-obvious cause, as in the case of my wife's Jeep a couple of years ago, when the heater fan gradually lost speeds 1, 2, and 3, eventually getting to where it had to be either off or on full-blast. I figured it was the switch -- but no, turns out there's a resister that gets rusty and causes exactly the problem I was observing, and every Jeep owner knows about it because it's going to happen sooner or later....

Urb

 

Ya, the AC and rear defog switches had occasional issues with getting stuck in the on or off position, partially stuck far enough to keep either system on, lights that may or may not work, and possible blown fuse.
So it could have the AC button pushed in, with no light indicating it's on.


Kinda wondering why the ac didn't work (at all??) sometime in the recent past, but now it does. Don't have enough info for all that right now though.