Having a slight issue with my climate control and hoping this is the place to post this. I've discovered in my '04 4x4 that when I turn my selector switch to the defrost position my A/C compressor kicks on. It blows out to the windshield, sure enough, but my spider sense is telling me the A/C should only come on when I select it. Also, and maybe related, my vent door comes open above 2000 rpm and will let fresh air in, no matter what my selector is set to. I've been hunting for a vacuum leak but to no avail. Any ideas?

 

Your A/C compressor should come on when you select defrost because it helps with defogging your windshield faster.

 

The compressor running on the defrost setting is normal, it removes the excess moisture from the air. Don't have any idea why the vent door is acting that way, though.

 

never had a vehicle do that with the defrost. nice to know that's normal. thanks.

 

Every vehicle I've owned does this.

 

actually gonna remove the fuse for the compressor when it gets cold enough to need it regularly. don't need the extra wear on my compressor or motor. still hunting for a damn reason the vent door comes open on its own.

 

It does it on my 78 nova and 69 gmc. Its not something new. Like said it removes the moisture from the air to help defrost and defog the windows faster. Frankly running the compressor helps keep it in shape vs letting it sit for a few months with all the oil draining to the lowest point in the system.

 

What exactly do you mean, "vent door"? If you're referring to the recirculation door, (next to passenger side kick panel) it should only be closed when you select MAX AC. It has one orange vacuum line attached to the actuator.

 

guess I'm thinking about this wrong, but I was under the impression that if the climate control was turned off, there should be no air blowing through the vents. never had another vehicle that did. HOWEVER, as my rpm's increase, so does the amount of air coming through the vents. all of em. no blower, just what can be forced in depending on how fast I'm travelling. so if I go 50mph at 1700rpm, nothing from the vents. drop down into 3rd, and I get air from the vents. on max a/c, where the recirculation door is supposed to be open and fresh air closed, if my rpm's go above 2000 I notice it starts blowing much warmer. which is a stark contrast to the way it should be, given the way a compressor works. it's letting fresh air in with the recirc. have no idea where to look, but am absolutely certain it's vacuum related. nothing else would be affected by the engine speed that I'm aware of.