Ford Ranger heater will not turn off, HELP

typical Ford heater:

Water always circulates through the heater core

Two 'doors' or circulation vanes in heater;

1. gating door - def, vent, floor

1. blend door - blower out to either heater core or a/c evap or both by degree

So you operate one at a time while looking at the actuators; the one that DOESNT move when you switch def to vent to floor is the blend door

Then if the blend door doesnt change when you move temp setting, it's bad control or tubing problem. If it DOES move but there's no change, the door has come loose from the actuator shaft.

Simple, no?!!

If you cant get it fixed immediately, disconnect hoses at firewall, and couple them together so that the heater core is bypassed