Blows heat all the time

SOURCE: My heating system only blows out hot air through the vents.

I've seen this problem alot. Replace the switch panel for the heater. There's a chip on the backside that likes to go bad. The part is a dealer item.

SOURCE: heater control 98 chevy s10 blazer

These trucks have a problem where moisture builds up in the heater box then freezes. When this freezes and you change your heater settings it breaks the shaft for the blend door. If this is what happened you should be able to look under the dash above and to the right of the gas pedal and you will see two vaccuum accuators one of them you should be able to wiggle around the linkage if it is broke. To fix this you need to remove the entire dash to get the heater box out which involves discharging the AC and draining the coolant because the heater core and evaporator come out. Please rate.

SOURCE: 1995 chevy blazer heat, ac will not blow air

yes the heater controls are vacum however the blower motor is not. a new control panel is an option and may fix it. if it was my blazer i would first check the fuse boxes onder the hood and in the side of the dash driver side. if they are good i would go to the nearest auto parts store and buy a test light. this will aid you in making sure what the problem is before you go spending money on replacement parts. the blower motor is in one of two places. its most likely under the dash on the passenger side. there is a cover that you will have to remove directly under the glove box. once removed you should see a large red and a large black wire. these are the power and ground for the blower motor . in some gm's these wires go into a resistor. the harness plugs into the resistor and the blower motor wires come out of it. ok now that we are a little bit familiar with our suroundings the red wire i told you about is the hot wire if you ground the clamp on the test light to the door hindge. (make sure its a good ground by touching the positive batter terminal. if the test light lights its a good ground )now unplug the blower motor and touch the metal posts in the end of the plug that belong to the red wire. if it lights when the key is on and the blower control is on in all posisions you need a blower motor. if it does not then you need a blower motor resistor.

SOURCE: AC vents on passenger side blowing warm air even

You will probably need a new RF temperature actuator which is on top of your HVAC box/under dash pad.($400 + at dealership.) I have replaced MANY....They get stuck and dont know where they are...If you want to try and recalibrate them yourself you can remove the HVAC/ECAS fuse in the underhood fuse block for 30 seconds(engine running) and reinstall the fuse and wait(IMPORTANT) 2 minutes...do not operate the a/c controls during this time...(engine still running) ..Then shut off vehicle and wait 30 seconds.. start the engine again and operate the A/C and see what happens....Hope this helps!!

SOURCE: AC blowing behind dash

on your vehilce it does not use vacuum to control the vent direction.
It uses a series of actuators (electrical).
My guess is that the air blows out the defrost (top vents) this is the default position for the mode door actuator.
More than likely it will have to be replaced.