i have a 1994 s10 blazer, 4.3, auto, 4wd. When i turn the heat on to high, it doesnt seem to blow as hard as my girlfriends 01 zr2 does. it still blows heat, but just not very hard. i didnt know if the 1st gen were known for that or if somebody might know of a way to bump up the force. Also when the RPM's increase, the heat will not come out of the vent until my RPM's hit a plateau. i am assuming that it is a vacuum problem within the engine compartment but didnt know if there was a valve or something within the heater box inside the dash. any help is appreciated.

 

The vacuum lines aren't just inside but also under the hood, there's a BALL thing on the passenger side, that "Stores" Vacuum, but you could also have a leak somewhere..

The most AIR you'll feel is when it's directed out the vents, you may have AC/Heat Door not moving too well becuase it's not getting enough vacuum due to a leak.

You can get a one way vac check valve, but not sure the best place to insert it into the system, at the least I would put it in before the BALL thing.

 

Also, your blower fan is pretty easy to get to inside the engine bay on the passanger side there should be some screw bolts around the ac and all that stuff, you could pull that out and make sure there is no crap in there.

Also, check the different settings, see if there is a difference between ac on with the heat on hot and check the different settings.

Verify that you hear the doors moving between each setting.

When youy have your heat on defrost, does it also come out the floor vents?

 

the blower motor is only a few months old and is clear of any debris. i tried different settings and it didnt seem to make much difference. i can hear the doors moving when i switch it. when it is on defrost, it also comes out on the floor but not very much.

 

My advice (as always) is to get a hand held vacuun pump. (Mity-Vac) You can check what doors are opening to see if you have aa leaky actator and also check vacuum as well as do a one man brake bleedingjob. One of the best tools ever invented.

 

I'm having a similar issue. I had to replace the heater controller because the faceplate was cracked and the connector for the blower motor speed got messed up. Now I know there's a vacuum leak in the heater controller, but I'm not sure how to fix it. It's plugged in as firmly as I can get it plugged in, but it still leaks (you can hear it when you move the heater to Heat) and the Vent option straight-up doesn't work.

 

These things are easy to fix. You do have to donatr a littke blood sometines. The nice thing about a hand held is you can work everything in slow motion or check each actuator separately.
Theonetruetom Thismunit comes apart with some little gears to move the controllrt. Make sure you have the thing in sync. (Trial and error - mostly error). Fortuneatley I have a factory service manual, but they all work the same. May I suggest your public library.

 

It may be an electrical problem. If your mechanicals are ok, your fan controll switch may not be working at high speed. It is a 4 speed switch, you should hear 4 seperate speeds when moving the switch.