Having a hard time figuring this one out so im hoping you all can help me out. the vents in my 89' blow out air intermittently. sometimes the work fine and then the next time i get in the truck and try to turn them on...nothing, any ideas on what could be causing this?

 

IDK which dash the 89 has in it, but if it's the one like the 93's with the two vertical sliders for the temp controls, mine was doing the same thing. The harness that plugs into the lo--hi swich was melted on one pin and it wasn't making good contact. I could slap the top of the dash by the switch and it would come on sometimes. I had to go to the wrecking yard and snag one and just wire it back in.

 

yeah the 89' and the 93' are the same, so a new temp control box may be the answer???

 

you could replace the whole thing but all I did was just change the 4 wire harness that plugs onto the speed selector switch.
I almost forgot, I also replaced the blower motor relay when I wired in the other harness also. I was having problems with it too. Being an 89, that might be part of the problem also. It was like 8 bucks I think from advance auto.