A/C Heater Control Unit has mind of it's own!!

[99'Yukon]

So for the past few weeks while driving my Yukon, I have started to hear this kind of high pitched sound that sort of sounds like a CD synchronizing coming from the dash area. It's not the CD player bc mine isn't even hooked up. I think it might have something to do with my A/C unit itself. Once the sound begins, even with my knob on the OFF position, the heat or a/c will start blowing on it's own. I am very perplexed at this situation, and have yet to find a solution to this strange problem that I'm having. My thoughts might be a vacuum line or something, but any other thoughts on this situation would be greatly appreciated.

 

[SunlitComet]

no vacuum lines really. at least not in hvac assembly. only for water valve under hood. if you mean actual blower is operating while switch is off you need to replace the fan switch in control head. they do cause issues.

 

[99'Yukon]

Are those switches (lo/hi-hot/cold-dash/floor) 3 separate switches behind each knob or are all 3 knobs part of a complete unit? If they are 3 separate switches, that would be great knowing that the fan switch would be the only one requiring replacement. If it does happen to be all one complete unit about how much do those usually cost? Are there any good sites to get these units from to save a little bit of money? I know those things probably can't be cheap lol

 

[SunlitComet]

the fan switch and rear defrost switches by themselves are replaceable. others are not.

http://www.amazon.com/ACDelco-15-72275-Heater-Blower-Control/dp/B0012P2KB4

Make sure to inspect the wire pigtail for electrical or heat damage before installing new one.
If needed: http://www.amazon.com/ACDelco-PT1346-Female-8-Way-Connector/dp/B000C9TZBY/

 

[LI99HOE]

Replace the fan control switch. you can find it on Ebay, or any gm supply parts place.
Fairly cheap, and easy to change. Link below is for reference.
http://www.ebay.com/itm/CHEVROLET-C...pt=Motors_Car_Truck_Parts_Accessories&vxp=mtr

I can't see the switch squeeling though... my motor was making this noise when turned on.... if it's your motor making the noise, you'll have to replace the motor ass'y w/wheel. Also avail @ above mentioned places, but more $$$.

 

[JBeezy]

Kinda late but I'm just searching. Could this be the same problem if the fan won't come on at all? When the vehicle gets up to speed you can feel heat coming out the vents but motor won't work by the switch

 

[SunlitComet]

yes, or its fuse.

 

[JBeezy]

What I just found out was the fan will blow but only after the truck warms up some when it's cold outside. Weird

 

[JBeezy]

Turned out to be a bad resistor. Dealer fixed it for $120

 

[robhenry2990]

ouch