Ok, so after several years of tolerating no heat, I finally flushed the core and have heat (also replaced the heater control valve so that is brand new). New problem is that regardless of where I slide the mix, the vents are producing BLAZING hot air. I am guessing its a problem with the blend doors, but I've never had the dash disassembled far enough to even know how to access them, if that setup even exists on an 89 model. Mind you, this pickup does NOT have factory A/C, but I have a donor truck (wrecked) that I plan to scavenge the A/C setup from and install this fall, once its no longer 100 degrees outside.

I'm just wondering if anyone else has had this issue, where the the heater is basically stuck ON. If so, does this model truck (1989) have a normal mechanical blend door setup, and what is the easiest way to access it to check its operation. I know I'll be neck deep into it this fall, to install the A/C, but I'd like to make it through the rest of the summer without the heater being perpetually on!

 

My first thought is to check the heater valve in the engine bay. It's mounted on the firewall right behind the intake plenum, where the heater hoses go through the firewall. There is a small cable through the firewall that pulls and pushes the valve open and closed. On my 93 there is nothing holding it in place, and it seems like it could easily slip off the tab on the valve. If that valve is stuck open, hot coolant will be constantly flowing through your heater core.

 

Yes, I replaced that with a brand new one when I flushed the core. It appears to be operating normally.

 

Pardon my selective reading, I see that you mentioned that now.

 

The passenger side dash is quite easy to remove (just the glove box really). You can see quite a bit of the ducting behind it, and I think it's how you access the blower motor as well. I don't know if you've been in that far but maybe worth a look.

 

I have had the passenger side off many times in the past, and I can see the blower and ducting, just wonder where in that whole setup is the blend door mechanism. It would be better to know before taking the whole thing off, lol.

 

I'd be in the same boat as you at that point. I'd probably try a mirror or just contort myself up in there and see if you can follow the linkage arms from the selector panel. Sorry I can't be more help, hopefully someone who's been there will come along and offer some advice.

 

Your heater control valve is not shutting if you still have heat in the cab when your climate control is in the COLD. have someone turn the temperature control to hot and cold while you observe the valve. If need to, use a plier to close the valve. I manually close and open my valve depending on the season due to me not yet replacing my rusty valve.