Heating and Ventilation - 1990 318i

[MontFenn]

I have a problem with the heater in my car. The heater seems to be either off or fully on, which makes it difficult to maintain a comfortable temperature in the vehicle. When I turn the dial up from the blue to the red, sometimes nothing happens, and sometimes hot air comes out of the vents. When it gets too hot, I turn it down all the way into the blue, and generally, then when it gets too cold again, turning it back into the red has no effect, the air is still cold. After a while of turning the dial up and down a few times, I often get hot air again.

I assume that components of the system include a temperature sensor and a control unit, and one of these is faulty. Is the control unit something that is easy to replace, or is this a subfunction of a larger more complicated part of the car's electronics?

[jbontke]

The blower motor resistor controls the blower motor fan speed. Most likely yours is bad.

The hot cold dial should control turn off/on the heater control valve (not sure what else it does) Make sure you get the same temps with the heater control valve open on the send/return pipe: https://www.r3vlimited.com/board/for...core-and-valve

[MontFenn]

The blower motor resistor controls the blower motor fan speed. Most likely yours is bad.

The hot cold dial should control turn off/on the heater control valve (not sure what else it does) Make sure you get the same temps with the heater control valve open on the send/return pipe: https://www.r3vlimited.com/board/for...core-and-valve

Thank-you for your response and the link to the repair instructions. From the details given there, I would guess that my control valve is faulty.

[jbontke]

Its possible, I would first make sure that the switch is getting the 12v to open it. Then verify that when the car is hot and the temp blend switch is on its hottest setting, the heater core upper and lower pipes are the same temp (meaning coolant is flowing through the heater core).