A/C compressor kicks ON with heat ON. Normal?

[jjrock5]

I noticed it was happening to my old 97 GST. I bought a newer climate control switch module but never got the chance to replace it since I sold the car.

Now with my 99 GSX, I notice that when I turn the heat on (AC button not in the ON position) the AC compressor starts kicking on.

I visually see it on, I hear it click, and my RPMs lower just as if the AC was on.

The heat still blows hot but Im sure my MPG is going down since the compressor is running...

Is this normal? Or is my luck that bad that it happened on both of my 2g cars??

 

[ramsack]

The AC will go on in every car if you use the windshield defroster. If the AC is coming on with any other mode then there is a problem.

 

[jjrock5]

Hmm yup that's gotta be it since I always keep my blower in the defrost position. Well that was easy. Thanks!

I'll have to check to see if it kicks on in any other position.

 

[LKWTSI]

The fact that your A/C is coming on is perfectly normal, when you put it on defrost. The compressor isn't just for pushing out cold air. The system is running and helping pull the moisture out of the air, from the water vapor that is added when the windscreen defrosts.

 

[ZenkaiRacerDsM]

Yep its normal. I think only the 95's don't do it. Its rather annoying and I'd rather have control over whether or not I want to dehumidify or not. In my civic I leave it in that position most of the time too since I'd rather not have hot air blowing directly in my face. And I cant really do that in my eclipse.

Normally I put it in between the defrost and the foot well setting just enough that the a/c compressor is not on.

 

[DSM1G90]

All cars with A/C kicks on the compressor in the defrost mode to keep the refrigerant and system in good operational condition, for if not used, the refridgerant will get contaminated and lose it's efficency from not being used and you'd be facing an A/C recharge every season.

 

[jjrock5]

Anybody know if installing a 95 climate control would stop making the AC kick on?

Or any way from stopping it?

 

[ramsack]

It kicks the defroster on not to keep freon fresh, but because AC removes moisture in the air, which is what would be covering the window. It dries the window and prevents condensation from further forming because the air is dried. I don't think refrigerant loses potency just because of sitting. Freon (r-12) has been around for decades and every molecule of it was manufactured long ago and none have just rotted away from sitting. The oil is one thing that would need to be cycled around the system once and a while.

 

[ZenkaiRacerDsM]

Yes I think the 95 climate control will do it. I swear I read about it here on tuners a while ago. But it looked like a pain so I've never tried it. Maybe you can find the post. And no not ALL cars do this. Maybe most newer cars do, but none of my civics ever did it. I hate that my eclipse does this.

Actually I just remembered from the same post that I remember from a while ago someone mentioned that there was a wire you can just cut on the back of the controls so it doesnt kick on unless you push the button. I may just search for the post myself now.

 

[ramsack]

It probably became mandatory a certain year. I don't think you can even get cars without AC anymore legally. My '01 Civic turned the AC on with the defroster. I can't believe it's illegal to remove climate control (for inspection, at least in PA.)

 

[PieEyedPiper]

It probably became mandatory a certain year. I don't think you can even get cars without AC anymore legally. My '01 Civic turned the AC on with the defroster. I can't believe it's illegal to remove climate control (for inspection, at least in PA.)

You can buy new vehicles without A/C.