How do I change the heater temperature control mechanism on 93 ranger extended cab XLT?

SOURCE: HEATER TEMP CONTROL IS STUCK ON HEAT. WILL NOT SWITCH TO COOL

sounds like your blend door actuator has failed, or the lost vacuum to this actuator, or something got into the vents holding the blend door into position. Most common is the acuator failing, good news is its a fairly inexpensive part, but gettin to it is not fun, its it the ductwork in behind the dash, I'm not sure on your specific model but most I have seen the dash has to come completely out. If it gets to that point you may want a repair shop to do that.But hopefully you get lucky and its easy access.

SOURCE: 1986 VW Golf heater blows cold air

The heater in your car depends upon a flow of hot coolant going through the heater core in order to get hot air into the car. If the heater core is partially plugged, it will restrict the flow. If you have a head gasket that is putting exhaust into the cooling system, it will eventually get into the heater core. When this happens there is no coolant in the heater core to make the air warm. If the water pump vanes have corroded away the result will be very poor coolant circulation causing the heater to not blow hot air. If your car is equipped with a heater control valve that is not functioning properly, the coolant flow will be restricted. One or a combination of these factors is likely the culprit in your case.
if the car is not overheating, the thermostat is working fine.... replace or flush the heater core multiple times to try and eliminate sediment build-up.

SOURCE: temperature control knob turns but doesn't change temp.

the heater control valve is visible through the speaker cut-out; it's at the end of the plastic heater control rod, inside the car - not on the other side of the firewall! It's connected to the valve with a plastic "universal joint".

Check that the valve is actually being turned by the rod. The connection might not be good (pulled apart or broken), and or the valve might be stuck.

Saabreur

SOURCE: Blows hot air , HOT air all the time regardless of temp setting

the climate unit has an internal fault

SOURCE: With AC on cold, Drivers air full hot & passenger side full Cold

that is a good possibilty, but before I pulled the trigger I would try this first. unhook the battery for 5 minutes, rehook it, now turn the key on, wait for 2 minutes, now start the truck and see if the doors now work. sometimes this works, its worth a try.

Testimonial: "Thank You, Temp. Cont. operates ok. A computer reboot on a truck works the same as on commerical aircraft system (reset system). hopefully no refault"