I just got done replacing the heater core on my '96 4-door 4WD. What a nightmare! If you've done one of these, you know the whole dash has to come out.

It now heats like the sun on the equator, but it won't switch among the various outputs. I.e., most of the flow now comes from the defroster ducts. You can switch the control, but nothing happens. A little bit of flow comes from the dash vents, and maybe the floor, too, but nothing like it should.

Incidentally, I did wind up with a black rubber hose in the passenger compartment that I can't remember where it came from. It was so long between when I took it all apart and when I put it back together that I really can't remember. Maybe it was part of the heating system & maybe it wasn't. It's about 9 inches long, a 1/2 inch outside diameter, and at one end it has a full right angle bend. Is this part of the vacuum system in the dash that operates the controls? Anybody with a dash apart that could tell me? Or does this sound like a defective control switch?

-Thomas

 

When all that works is the defrost That is the default setting. You most likely have a vacuum leak someplace.

 

+1 to blazerguy. either that or you didnt hook up the vacuum line all together. ive done that myself before. with my company we have 5 s10's. (1) 2 door blazer, (1) 4 door blazer (mine), 2 extended cabs 1 4.3, 1 2.2, and 1 standard cab 4 banger. i had to do the heater cores in 3 of them in 2 days. i got one done the first day and did 2 the second day. the last one i did i was finishing it up when the sun was going down and i forgot to hook up the vac lines. only took 5 minutes to fix it.