A/C Comp just kicks on... Why? 01 XJ

My A/C compressor will kick on about 8 seconds when I am just running heat. I did a little off roading and it has done it since.

Also my heat only blows out of the defroster no matter were the knob is set, would that be something unhooked in the back?

Thanks any help would help me keep my hair!!!

Since the A/C system is set to run when you are in defrost mode, I would assume that is why it is running now. The reason you are stuck in defrost most is the mystery.

Most modern automotive HVAC systems use vacuum motor operated valves to control how the air is directed. The vacuum is supplied by the engine, tapped off the intake manifold and brought into the HVAC control panel to a central mulit-valve routing switcher. When you twist the knob controlling the heat, vent, defrost, A/C functions you are sending vacuum to the appropriate vacuum motor operated valve(s). If a vacuum line has been broken, a vacuum motor is faulty or the main routing valve is leaking you could experience the situation you've got. And as already pointed out, the A/C compressor will kick on during the defrost mode....which is apparently the mode your stuck in.

Unless you really want to delve into the dash of your XJ, this might be a case where the dealership is your best bet for repair. At the very least, have on hand a factory service manual befor you go digging into it.


mike

I've always wondered, why does the a/c pump kick in when the defrost position is selected? Both of my XJ's have done it and even my Ford work van does it... I've thought about disconnecting the a/c clutch electrical connection in the winter months, would that be evil...?

I've always wondered, why does the a/c pump kick in when the defrost position is selected? Both of my XJ's have done it and even my Ford work van does it... I've thought about disconnecting the a/c clutch electrical connection in the winter months, would that be evil...?
That wouldn't be evil :evillol: , just less effective :smokin:

While cooling the air, Air Conditioners (ALL of them) also remove moisture from the air. That's why water drips out of most AC units.

I ORDERED a 1983 Chevy S10 (my first "new" vehicle) that did not have AC. The defroster worked, but I had to WAIT for the engine to warm up before it was any good at all.

Take Care,

The A/C compressor dehumidifies the air, so even if you're not blowin cold a/c, if its on the windshield defrost mode, or feet air with defrost, the a/c compressor is still being used slightly to remove the humididty. If you put the knob on say just vent, or foot air, it will stop cycling on and off. It isnt anything to be worried about, my jeeps always do it. if you do want to unplug the compressor when you wont be needing cold a/c it will not matter, but your defrost air wont be dehumidified and therefore will defrost less effectively. As for being stuck on a certain setting, its probably is a vacuum line, but not sure. Best of luck

That's AWESOME! I would have never guessed it was removing moisture!
One more mystery of the universe solved...:ylsuper:

As has already been stated, it does the dehumidify routine which increases the ability to defog the glass but.... it also helps to keep the seals on the compressor and other A/C system components lubricated. Used to be the compressor wouldn't run in the defrost mode and after a long winter (and in some parts of the country we are talking L-O-N-G) and Spring season of non-use, the seals would fail (dry out) and the system would need a recharge. And since we are talking freon leaks, well you can figure the rest out.