Probably the Heater Fan Thermostat. It may have a different name.
Defective heater blower motor resistor pack.
Take out the glove box there you will see the heater motor the back of that is the resister you will need to get on yyour back to reach up to it.it should slide out
The most likely cause is a bad blower motor resistor.
The blower motor speed resister may be burned out.
Same problem vectra heater only blowing cold checked water coolant and it was empty. Topped up now blowing hot just hope I not got head gasket probe
how is it my heater control on my ford fiesta flight 1998 only works on no. 4
The heater motor speed resister is burned out.
Possibly
replace front heater corefront and rear have independent heater cores
Replace heater motor resistor.
The blower motor speed resistor is burned out.
2001 dodge ram 1500 ac and heater flow regulator switch does not work. works only on defrost. How to fix?