Heater control 98 chevy s10 blazer

i'd think that the vent adjuster knob/slider is not working correctly strip out the heater panel around the control knobs and check the vent direction is working properly either stiff operation so a little wd40 on the cable would probably do the trick or some thing causing the vent itself to not move

Transfer case switch may be bad allowing trans fluid in vac. Lines and can reach as far as heater switch common problem fix these all the time 17 bucks for tranfer case switch and 20 foot of vacume hose and replace all the vac. Hose because this issue causes pcv to not work correctly so the moisture from crank case ends up going out the distributor vents causing cap and rotor corrosion there is service bulletin to remove distributor vent screens i would fix that since you will be working next to it any way

I assume your heater setting is electric control, if so either your defrost and floor heat switch failed or wire problem. For the air not hot, check the heat control valve on the top of the hose it should be in front of the firewall. I don't know your car is using mechanic valve or electric control valve. Anyway check there first. Good luck.

Could be the main control panel. The ac clutch will engage if it gets power and the system is full of freon. The air should switch to the other vents even if the ac clutch does not engage.
You may need a shop manual to get the wiring diagrams to troubleshoot the system.

It sounds like you have two problems. First a question though; Is your heating and air conditioning control on the dash automatic (has two knobs that rotate and a display screen in the middle), or manual (has two levers that move up and down for driver/passenger temp and a separate fan knob and mode knob).

In response to the vents being stuck on defrost and floor, from experience i can say that the most likely cause is the mode actuator has failed. If your battery has recently gone dead, that could have brought the problem to the surface. When the battery has gone dead, the heating and air conditioning controls relearn all the positions of the actuators behind the dash when the vehicle has been re-started. If there is a position sensor failing (which happens quite often) in one of the actuators, the heating and air conditioning controls won't be able to learn the correct position of the actuator and (in your case) defaults to the defrost/floor position.

The only way to fix that would be to replace the actuator. I would like to know what type of heating and air conditioning controls you have (manual or automatic) before i say anything on the blower only working on 5.

If you have warm air coming through the defroster vents then your core is not gone. there is something blocking or bent on the heater box mechanism which directs the air flow up or down, or on the climate control knob which controls it, or in the cable which connect the two.

your leak is probably in the control unit itself . try checking the vacum conection on the heat control

you have a bad control switch.

Check blend door motors under dash on heater box. Move heater control and see which one is not moving. That's the one thats broken or sticking!

i would say its in the dash unfortunately you will have to pull it out to inspect.