my friends heat stopped blowing in his 89 RS. With the windows up it gets hot in the car but it won't blow hard out of the vents. any idea what it could be? he is complaining about it being cold and can't be warm while smoking cigs. ty

If the defrost is working, then he has a vac leak. Put an ear to the HAVC controls. If you hear a hissing there, you've found the leak. A new valve should do the trick: Valve Vac Sel GM part # 16032395. If there is no hissing, check the black plastic vac lines under dash and under hood.

JamesC

i sent the msg to him i'll reply later on what he says

he says there is a hissing sound and nothing works he says

I am having the exact same problem. I replaced the blower motor, which made the defrost blow harder (enough to keep it from fogging) but its still too cold in the car. I hear a hissing sound behind the controls. Is there another way of explaining the part you mentioned to someone at autozone? They didn't know what I was talking about and the part # wasn't working for them (I don't know that they go by gm part #s)

Welcome to TGO. This is probably a dealership item--or you can order from the following site:

http://www.gmpartsdirect.com/index.c...TOKEN=43475709

JamesC

ok i looked at it myself b4 i was just going by what he was telling me. on full blast nothing blows at all and when u switch to defrost it makes that hiss sound for like 4-5 seconds. what will he need to fix it?

This sort of problem 'can' be confusing. I believe the MOODE switch is vacuum operated. The MOODE switch is the one that makes the air come from the floor or panels or defrost or vents, etc. It operates the doors { in part } that direct the air to the appropiete setting on the switch. If it is not functioning correctly the air could be moving out of all the vents at the sametime regaurdless of where the switch it set. Hence the slow moving random direction of air movement. Kinda like standing 3 inches in front of a house fan, or across the room. You would need to search this problem from the begining.
Are you getting vacuum to the switch?
if so
is it air tight connection at the switch ? {no hissing}
if so
when you change the moode setting does the appropiete door open/close without any hissing 'after' that particular door has been opened/closed ?
if it continues to leak vacuum you have a bad moode switch or maybe a broken vacuum line
if it doesn't continue to hiss
each door has a vacuum actuator control...are those working correctly ?
{they are like a enclosed vacuum diaphram that has an arm that physically operates the door/s via a metal rod}
Your sure the fan is blowing correctly ....right ? meaning its functioning on all speeds.
NOW HERES THE TOUGH PART
If all that is working correctly, and the blower motor is actually blowing on all speeds.
Field mice often get inside cars and build nests
Inside the heater box and vent work there is foam striping. When those doors close, they close against the foam for a more air tight seal. Sometimes that foam dries out and comes loose from the inner duct work and gets trapped in the doors. Making it impossible for the doors to close completely. Or even clog up a portion of the ducts. And then all the air is misdirected.
Pray thats not the problem....LOL
If it is, you have to completely remove the heater box, vent work from the car, then separate it, and open it up. I don't car what you read, or what your told its a freaking terrible awkward job. Very frustrating and most shops won't even do it. Its the same as installing a heater core or A/C evaporater. EWWWWWWWW
I do this for a living. Take my word, take as much time as you need, and assume nothing. You don't want to get involved in removing that heater box and duct work unless you are 110% absolutely sure you have to.

Before you do any purchasing or hard work, (this is going to sound stupid but it's a common mistake) did you check the coolant level? The heater in a car is run off of the heat of the coolant and if your coolant is low than you're not going to get any to the heater core. Before I dropped out of college for a medical emergency I did take the heating, air conditioning, and cooling class. My heater core was bad and fogging up my windshield with coolant vapor and dumping coolant on my floor and it's a lot of work to get to the air box behind the dash.

WHAT JOINER SAID !!!!!!!

yeah, I have to agree 100%. I just spent 2 days changing out a heater core and it's a brutal job. I had to take apart the entire passenger side of the dash to reach one bolt at the top of the heater box so don't change that thing out unless you know it's bad!