The HVAC doors that control the airflow are activated by small vacuum motors. The system is designed to fail safe; this means that the system will fail in full defrost mode. So, knowing this and the fact that you have heater but no A/C or defrost you should assume the system has a failed control head (the part that you select functions with with button or lever). Or the doors are stuck due to an warped duct system (usually high heat related).
Why the heater or defroster may not work in a 1993 Chevy Caprice Classic because of the heating core is going out.
its the blower resistor.
There are multiple reasons why the passenger heater on a 2007 Chrysler Pacifica may not work. it could be a heater coil, a fuse, or the blower. A mechanic can help figure out the specific reason.
Depends on what you mean by heater will not work. If the blower motor will not work, it can be a blown fuse, bad blower motor, bad blower motor switch, or a defective blower motor resistor pack. If you mean that the blower motor works but there is no heat, then it can be a clogged heater core, thermostat stuck open, or defective heater control valve.
There might be a bad fuse causing the heater to not work. Check the fuses if they are all ok you may have a bad blower motor. when you turn the heater on and no air is blowing then it is your blower motor.
You most likely will have a bad blower resister........
replace heater relay and or heater blower motor
One reasons a Dodge W 250 defroster may not work is the blower motor relay. This can be replaced easily. If it isn't the relay, there may be a problem in defroster door binding. A mechanic will be able to determine the cause.
if there is a lot of snow or ice on these vents located at the bottom of the wind shield under the wipers that could be the problem if you live in a cold environment.
probably the blower motor resistor
heater blower resistor has to be replaced. you have to remove glove boxthe resistor is to the right of the heater blower moter