I have an 07. It is cold here now in Indiana and I've noticed when my defrost is on, blowing warm, that there is a small jump in the RPM. it lasts about 2 seconds then stops, repeats.

The a/c blows cold and everything works fine. When i dont have it in defrost it doesn't do it. I seem to notice it when I'm in park or at a stop.

Car runs great other than this. no other idle issues.

Any help would be great. Thanks everyone!

 

I think it is just the A/C compressor cycling on and off -- the defrost uses the A/C to dry the air before it heats it

 

I've read that too. Should I be worried? The car is all stock. The only thing I've done to it is add an aftermarket head unit and a back up camera..

 

How big is the RPM jump? It's probably nothing to worry about.

 

Barely anything lol. I can just hear and tell that its doing it. The rpm needle barley even moves

 

pretty sure it is normal . . . when the engine picks up the load of the A/C compressor it surges the RPM a little, just to get the compressor turning then it settles back down

 

Why would the compressor be kicking on if im using defrost and dont have the ac turned on?

 

Heater alone will cause the windscreen to fog up as the moisture in the air turns into a very light, but very much there, steam. The solution is to pull the moisture from the air, make it drier. The A/C system can do that, so they route the air through the A/C, then through the heater core, then to the windscreen. It's always used thusly. You can turn off the A/C for the other settings, but not that one (nor Max A/C, of course). Cars have been set up like this for a while now, it's a safer, faster way to get the windscreen defrosted/defogged. And some days, if you didn't have that A/C setup going on, it will be impossible to get it to work because the air is so humid.

If you're in a cold desert, sure, it'll work. But then, it probably won't be frostin'/foggin' up in the first place, not a lot of moisture going on in the first place. It could still happen, sure... But I can tell you that if you are in a rainy day/night and you try to defrost the windshield in Houston (for example, probably Tampa or Seattle or others can be made examples) without the A/C? Yeah. That's a hoot. The old cars I used to drive were miserable about it, because they didn't have A/C. So fun. Had to have a lot of napkins/paper towels/towel in general to wipe the windshield off on those days. Windows cracked sometimes helped, sometimes didn't... You really don't want no-A/C for defrost, lemme tell ya...

Hope that helps!

 

. . .whether you turn on the A/C or not

 

Agree with all. The compressor is used with defrost to dry the air. It will cause extra load on the motor, so it causes a surge in RPM to compensate when at idle. All normal as long as it is just a slight increase as mentioned. You are all good.