heater ???

the heater in my '91 chevy p/u is not blowing hot air...i just blows cold air....it was working fine ...now its not....what could be the problem??

Heater core may be blocked. There are two heater hoses going to the heater core. Both hoses should be warm to the touch. If one of the hoses is cold to the touch, the heater core is blocked.

You can try to backflush the heater core to clean in out; otherwise, it may need to be replaced.

//2000CAYukon

thx

The damper may be stuck. I've known quite a few instances of this as well as my own a few years back.

actually my truck once lost heat when idling and it would work when i was moving with the engine above idle speed. i discovered that my coolant level was extremely low and that accounted for another problem of my truck overheating at idle then cooling back down when revved up. i guess you could say i was an idiot

where would the damper be ???

The damper is underneath the dash on the passenger side. If you look under the dash above the passenger floorboard you will see what looks like an irregularly shaped black plastic box. This is the heater assembly. I've change the heater core once in my '88 but never had to mess with the damper. I just played with the temp setting back and forth (for quite a while on several instances) until the damper began to move again. I found that if I set the temp control one notch from being completely hot or cold, the damper wouldn't stick and hasn't in the last 10 years or so unless I accidentally set the control all the way. To get at all of the assembly bolts, you need to take out the passenger side kick panel, the glove box liner and computer. This is all straight forward. I've changed the heater core by etching and breaking a section of the housing out then screwing it back (didn't feel like removing all the crap a manual said to) but I've never actually laid eyes on the damper in my heater assembly since I've gotten by with it. The Haynes manual for this year doesn't specifically mention servicing the damper. If your heater hoses are both hot (means hot antifreeze is circulating through the core) when the engine is up to temp and your blower motor is working fine, there isn't anything other than the damper to block the hot air. Sorry I can't be of more help on the actual damper other than to suggest getting into the assembly and make sure the damper can move on its own.