I was just wondering if anyone has disabled the ac compressor from coming on when the dial is set to defrost/defog the windshield. This just bugs the heck out of me when Im driving and the ac compressor is clunking on and off. Not to mention dropping my MPG further than it already is since the car is so fun to drive. If I want the ac to come on I THINK there is a button or **** some where on the the dash for that.

 

If I understand what you're asking , just push the a/c button and it should turn off ...

 

The ac light never comes on, but I will try it. The compressor kicks on automaticly.

 

Every single car I've owned that has had AC did this. The best thing to do is to turn the cold/warm air selector to warm side and the AC shouldn't kick in. The reason the compressor kicks in with the defrost is that AC also drys out the air passing though it, thus clearing your windshield. With the heat on (which you would normally have on in the winter) it wouldnt make any sence to turn the AC on.

I haven't noticed much if anything change in my cars MPG since I've been running the AC on it the past couple days...my MPG has actually gone up since I've used it

 

That is exactly why the compressor kicks on with the defrost. If I am not mistaken EVERY car does this.
I even had to take a parts guy out to my last car and prove to him that the compressor does indeed kick in when the defroster is used, and regardless of where the Heat selector is positioned.

 

Most modern cars do this, but not all. The compressor DOES NOT ENGAGE IN COLD WEATHER. Below a certain temp. (at about 45 degrees), the A/C will not turn on.
In many cars, that temp. control switch is in the compressor. You can add a cut out switch (solenoid) to the compressor and it will do the same thing.

 

Raise the temperture selection.

 

Actually, run the car on heat and a small amount will go to defrost the window and the A/C won't turn on. A/C won't operate on heat unless you hit the A/C button.
On defrost, it's automatic.

 

the ac is automatic, it is to chage the humidity of the air on the inside of the car. To be honest, i would just leave it alone. turn the defrost on, get the windows cleared off, and then just kick it back off. With the a/c on, it will help clear the windows much faster. The change in fuel mileage is minimal from just the defroster.

oh and another little tip that somehow some people just dont understand (some, i am not saying everyone here does this... just a thought if anyone is reading this and wondered why their windows wont clear sometimes)... a defroster will pretty much never work if you leave it on the recirculate, you need to pump fresh air to get the windows cleared out properly. i have noticed it especialy true when it is raining.

taking HVAC in college is such a curse and a power... i look at everything in terms of heat and humidity now.

 

I think it actually says in the owner's manual (I sometimes do rtfm) that the A/C is activated when the defogger is turned on.

I believe the real issue is the clunking compressor, which others have complained about before. I don't know that I've heard one quite as loud as this current one.

 

This is turned on by default for a couple of reasons. One is dry rot. The rubber fittings etc. This keeps the system from drying out and malfunctioning. Big problem in the early AC years. And secondly health reasons. To prevent mold and mildew buildup in the Cabin section of the AC unit. Dry air....no mildew.

Thanks
Cheers!
Irish

 

Yes my biggest peev was the clunking compressor, did try running it with the selector to the floor and got enough air to keep the windshield about 90% clear. Didn't think about the air being dried by the compressor. Luckily I live in coastal So Cal, or Nor Mex if you prefer, so I don't have to run the ac to often. Windows down, listen to the song of the engine and exhaust. Thanks for all the input.

 

totally with you on the clunking compressor clutch ... why is it like that? makes me chuckle!

 

The AC compressor doesn't come on in very cold weather because the low pressure switch in the system is always open. The gas cools and that little ideal gas law says that the pressure drops with the temperature in a closed system. Eventually, it will get so low that they low pressure switch activates (it is there to protect the compressor. You have to have enough gas in the system to move the oil), shutting off the compressor until the temperature rises.

All in all, it is good for the AC system to be used during the winter months. If you compressor clutch is clunky, you might want to take it in. Mine is VERY quite (but I do have a coupe and my windows are almost always up).