My heat has been stuck on ever since I bought this blazer. I just bypassed the heater core in summer. But now I'm trying to get the a/c working. I have climate control and this is on a 1998 LT 4door blazer.
I used a 7mm,8mm,and 7/32 sockets(7,8 to take out glove compartment and all plastic under dash. 7/32 for the two screws on the actuator itself.).Remove all plastic under the dash, then remove the glove box. When you look in the opening you'll see the vacuum actuator for the blend door to change where the air comes out. I unplugged the vacuum line and slid the actuator up and out(just to give me more room). The temp actuator will be sitting on top of the heater box, and kinda behind the tubing going to the vents. Unplug the wiring connector to the actuator. If you have big hands it will be hard to get to the screws to take the temp actuator out. Then Keep the long end of the ratchet pointed to the drivers side and be patient... you'll only get about 1/4 turn at a time. Then I had to use a long screwdriver to pop the actuator off of the blend door.
And the most common problem is what was wrong with mine... The gear inside the actuator is cracked. When you get the actuator out you can turn the temp/blend door by hand to make sure it's not the problem(I turned on the truck to make sure I had heat one way and no heat the other) And I found a good tip for checking the actuator while it's out (other then taking it apart like I did for pictures)... After you get the actuator out, plug it back in and turn your key on. Then turn your temp from hot to cold and see if the actuator turns (hint: feel if it's working our put your ear against it to hear if the electric motor is humming. If no humming= possible no power.).
Hopefully this helps in someway to somebody.. Also once I get it put together I'll see if this fixes my problem of my heat being stuck on, and my a/c compressor doesn't come on when the a/c button is lit up.

 

I'm also going to buy an actuator for the non-climate control from a salvage yard and see if the gear is the same. Heck, even if you didn't want to try and get a used one. The non-climate controlled actuators are around $40. I'd rather spend $40 and switch gears before paying $150+ for the 5-pin electronics. I'll find out and keep updating.

 

Just got mine done yesterday....yep 144 bucks for it but the mech put it in for 20 bucks after I showed him how to get to it, a few bucks but was done in less than an hour...works great!

 

If by chance "closer" is still around:
how does the vacuum actuator come off of the air box? You stated in your posting that you slide it off....I have pulled and pulled with no luck. Is there a clip or something that holds the actuator in place or something??? Does it take a screw driver to pry the actuator up? I sure do not want to break it.

Thanks

 

The actuators clip in and were clearly designed for assembly, not disassembly. The pic below shows an example of the plastic clip. For this actuator, the clip has to be pulled down for the actuator to slide off the bracket.

 

Mine was fairly easy to get un-clipped. It's hardtelling how many times it's been taken off with 112,000 miles. But I still had to use a flat screw driver to help me get it out of there. But I'd do some more searching... If I remember there's more than one vacuum actuator. I think that one is for the max a/c (recirculating air) door. The tempature actuator is electronic on top of the heaterbox. And I thought there was individual vacuum ones for the dash vents, defrost, and floor.

 

You mentioned that you were going to see if you had heat or cold. That is hoew I dound out that my A/C was infact working. I would get the condensation build up. So I would tell any one looking at this post. If you have condensation under the truck and hot air. Then you have the fix right here. Just posting here on yours to help others that might read. Plus!! know if you have the manual selectors or the electronic selectors. For me it is time to switch back to regular heater core connection. Have had it looped during the hot months.