how hard is it to change out on a 91? the reason i ask is that when i press the floor vents or the top vents or any, there is no air coming out even with full blast. occasionally the defrost will come on. is this the blower motor or something else?

 

Having barely worked on a car before, when i got mine, i had basically the same problem as your having. I changed mine in about 20 minutes.

 

how expensive and how much of a pain in the ***?

 

Are you sure the doors are open? don't remember what year(s) but I though some were operated by vacum-could be wrong though.

 

i have know idea. i guess i ought to start taking the dash apart and find out.

 

The blower motor isn't too expensive and is quite easy to remove and replace. rick lambert is correct in that there is a door under the dash that must open and close correctly to direct the air into the proper ducts. If you remove the blower motor and look into the opening you can see the door. If the motor is bad, the plastic "squirel cage" is easily removed and put on the new motor. You probably don't need a new cage. Some motors come with a new one attached and some do not. The 90-91 blower motor is GM part #22098837.

 

I think this may be the answer I've been looking for. I've had same A/C & Heater problems when set above 5. I bought the blower control module and that didn't make one bit of difference. It's just so hard to look up under the dash much less work on it. O'h well I'll go pop another and have it.

 

If you do have a blower door problem it shouldn't be that hard to fix/adjust. In the C4 103 Class that Gordon Killebrew teaches in his school in TN, we covered this very subject on my 88. I believe that the door in your 91 is slightly different from mine in the control attachment setup, so I cannot help there, but others may be able to. If not, Gordon can probably answer your question on the door control linkage by phone. He charges $10 for the call and $2 per minute, but he knows this stuff inside out.

Living in Arkansas you can drive up to his C4 school and take his classes easily. I had to drive all the way from CA, but it was a fun trip in my 88 and worth the drive.

 

With the exception of the Temp door - driven by motor or a cable - all of the HVAC doors are vacuum operated. Look at the vacuum diagram in the engine compartment for the line labeled HVAC. Vacuum flows from the source through a three way check valve which is either to the left of the distributor or under the fuel rail. When the valve breaks or if vacuum is removed from whatever controls the door position, all you get is defrost. That valve is the first thing to check. If good, then manual air controls vacuum at the panel - electronic at the Programmer, above and to the right of the accelerator.

Quantity of air flow usually has nothing to do with vacuum (if it isn't working, it's all going to blow through the defroster but the amount of air will be quite good). Insufficient flow is generally because the duct work is leaking. It's sealed with foam that falls apart with age. A quick test is to remove the passenger side hush panel. If you have a nice stream of air at your feet, the seals are probably shot. To access, you need to at take off the crash pad. Reseal defroster and vents with duct tape (or whatever you can find at Home Depot).

Another source is the Evaporator Housing - particularly where it's split and at the firewall. If you can feel air at any of these locations (and don't forget to feel underneath it too), it can be sealed back up with window ribbon sealer - a nicey gooey clay like substance that's easily molded and trimmed so that it looks OEM. Most housing leaks are because somebody replaced the evaporator and didn't bother to seal it back up right (opps - guess how I found that out!).

If you suspect the blower motor, jumper it to the battery first. If it blows stronger, it isn't getting enough juice. Check the wiring. It's marginal for the draw (old motors can suck 25 amps at max). If it's discolored, take apart the weatherpak and solder the connectors (they're only crimped). That should stop any voltage drop.

 

Wow! You drove from Cali to TN to Corvette School? I didn't know there was such a thing. Got to love it.

 

Yes it was a fun trip out and back. The C4 school that Gordon holds in Cross Plains, TN is a really great experience. It is a case of having the world's C4 authority diagnose your car and give you reference tips on repair and maintenance for 8 hours a day. I recommend it to everyone who owns a C4.