Heat is stuck on.
 

I just got a 1998 Blazer, but it seems the environmental controls are bad. The vent speed is stuck on very low, and the heat is stuck on. The vent controller seems to work though. The previous owner seems to have tried to jury rig a fix, I found a toggle switch attached to a long wire which disappears into the the passengers side dashboard hidden in the glovebox. When I flip the switch, the fan goes to high, but it is still stuck on heat.

How do I fix this properly, and turn the heat off? How much will the parts cost me? Is it difficult? I can use basic hand tools and follow simple instructions, but if it’s like my last car and requires me to take off a bunch of random plastic covers and disassemble half the engine just to get to one part, or somehow reach my hands, and a ratchet, into an area a quarter of an inch wide, I’ll have to go to a mechanic. How much would a mechanic charge for that?

I have no idea if the air conditioner still works, but assuming it does, how do I charge it?

For one thing, it is worth looking to see if the Blend Door Actuator is bad. It is not an uncommon part to fail. Lots of videos on checking this.

As for the fan speed control, if it is not an Computer Climate Control system, i.e. you tell it what temperature to maintain, there could be something wrong with the blower motor ballast resistors. That is easy to get to. If the resistors are bad, a new control panel for the HVAC might be in order.

While you are at it, you should look into at least checking if not replacing the underhood vacuum lines that supply vacuum to the HVAC actuators and the front axle engagement for the 4wd. I have a thread on doing that for my Auto-4WD system but it is similar for all 2nd gen Blazers. (see my sig file.)

Good Luck