Big Willy

My A/C work great. My heat works great. However, when I turn the heat on and select the Defrost setting to blow air on the windshield, the A/C compressor starts to run. I have heated air blowing on the windshield. The temp setting is in the 80's. I just don't understand why the compressor runs. It only does it in the Defrost position. The motor that controls the Air Blend Door failed last summer. Could that be why?

1989 Coupe

Thanks
*****

GreyGhost

The a/c will kick on when you put the defroster on..its normal. The a/c tries to pull the water out of the air.

flannel_man

newbecorvetteguy

Yep, normal condition. Don't understand how you didn't notice it before. Every AC equiped vehicle I've ever had works this way.

Mr Mojo

94ZR1

It helps defog the glass
All A/C cars do it

Big Willy

Thanks. You Guys always come through. Good to know I don't have a problem.

*****

Paul Workman

Nobody said you didn't have a problem. But, your A/C is working normally.

(Juuuuuuust pullin yer chain! )

P.

All2kool

You've never owned an old car.

You can disarm this feature by disconnecting the plug at the Compressor. Won't hurt a thing to do this. Been running unplugged all winter.

jrzyvet

So then I guess it would not be normal if I just had it on heat. Mine comes on when just the heat is on????

65Z01

I think my '88 with electronic HVAC control does not run the A/C when in the "heat" position.

BTW, you likely should run the A/C periodically (e.g. in Defrost) during cold weather just to keep lubricangs fresh in all the system.

robertt43

Its not a good idea to unplug your air for the winter. Its a good idea to circulate the air compressor once a month during the cold months,to keep the seals oiled and the clutch from sticking.

swifty

There are several settings for directing the airflow, and most of them run the compressor (GM cars only concern). With my '93 there is only one setting that leaves the compressor off (automatic climate control) - the one that directs the air through the upper vents on the dash. Same with my '99 Blazer, same with the SO's '98 Monte. The trick is to find the setting that doesn't rob you of as much horsepower and learn to live with it. You never know when the guy in the lane next to you will ask for a lesson. (I mean at the strip, of course.) One of the few reasons to not like summer - the need to AC with it's concurrent power loss.

RTFM - it's buried there among the other jewels. Good luck.

BADDUCK

I hate summer! (you can only take off so many clothes), so does my Vette. We both love winter and run better.

Paul Workman

I always heard that it is a good idea to run the AC compressor a little in the winter to keep the seals from drying out (or whatever). With the AC compressor coming on with the defrosters, it dries the air out for better evaporation, AND keeps the system lubed, etc. I'm NOT an AC engineer, so I speak not from any qualified knowledge, so I dunno. But, it makes sense, and the manufactures have been running the AC compressors on AC cars for decades.

newbecorvetteguy

Define old car. I'm 50. The first AC equiped car I owned was a '77 Ford LTD. It worked like that. I worked in the shops of GM/AMC dealerships in the 70's. Those cars worked that way too.

At GM school they gave reasons for having the AC on in the defrost position as drying the air to help remove fog off the windows and wanting the AC to cycle in the winter to keep oil circulating to prevent the compressor from siezing at start up for lack of oil after setting idle for months at a time. Same reason given for having the fan running all the time. They felt it stayed lubed better and would last longer running all the time than if it didn't run for months at a time. Don't know if that holds true or not. A lot of vettes set for 9 months or more out of the year from the time they're new.

As always, engineers design things to operate the way they do for a reason.