Hello,

 

 

I have a 1989 GL 10 AWD that has a defrost problem. This car has AC, which works, I can get heat but I can not switch between "Heat", "Bi-Level", and "Defrost". The Heat, Bi-Level, and Defrost buttons work but when any of these three are pressed it just stays on "Heat". I can switch from the 3 heat choices and the AC and it will switch back and forth, I just can’t switch between the 3 heat choices. Any help??

Sounds like you're missing the vacuum line to the heater controls. Very common problem.

 

Under the hood on the passenger side should be a clear-ish vacuum cannister with two vacuum lines going to it. One goes along the firewall then into the cab, and the other goes to the intake manifold. Most likely this line has come undone. Just find it and reconnect it/test if for a vacuum.

 

If that line is still there it could be that the vacuum cannister is broken, or there is a leak in the vacuum lines somewhere.

 

I had the guys at 'iffy-lube' knock this vacuum line off a few years ago... took a little looking but got it reconnected eventually.

There have already been a couple of threads in the last month dealing with this. Look them up, and if the fixes suggested there don't help, then we can try to help you more.