Defroster/Heater problem

[cam69ss]

I have a manual climate control car and when I put the car in defrost mode with full heat, I hear the AC compressor cycle on for a few seconds then off for 10 seconds, then back on again. Does anyone know what causes this? A vacuum leak somewhere?
Thanks

 

[salvageV6]

Usual problems would be low on freon or else a bad pressure cycling switch on the drier.

What type of freon you using?

 

[cam69ss]

Still has R-12, but I didn't think the AC compress. would turn on if if it is set at hot an defrost. I only think newer cars use the AC when you put the defrost on?
Dan

 

[Sleeper-6]

Mine does it too.

I believe it's normal, not only does AC cool the air it also removes the moisture from it. So hot dry air will do a much better job of defoging the windows than warm moist air.

 

[Tony sy2356]

It is normal for the compressor to cycle on when in the defrost position.

Tony

 

[salvageV6]

Not every 10 seconds it isn't.

 

[Sleeper-6]

Nope, qwick cycleing, as you said salvage, usually indicates a low pressuse condition.

 

[Tony sy2356]

Depends on the ambient temp. Low temp = low pressure= quick cycling.

Although the car likley is a bit low on charge. Disconnect the pressure cycling switch on the accumulator for the winter if you'd like to get rid of the compressor cycle.


Tony

 

[cam69ss]

Ok thanks for you help guys, I will worry about the AC in the spring. I just thought something was wrong with the climate control. Never new the AC turned on for defrost in the vintage '80 GM cars. I guess I never noticed it because I didn't hear the compressor cycle on and off before.

Dan