Questions and Answers
Mazda Has No Heat
Q. 1990 Mazda B2200 pickup, 4 cylinder , manual transmission, 143,000, 2 barrel carburetor, no ABS, rack and pinion steering, no A/C, no cruise. I have a heater problem. I replaced the thermostat and the coolant is heating sufficiently. The heater will only heat, but even then rarely when the fan is on the lowest setting. It never heats on a higher setting.
I have been told that if the heater core does not leak that it should be good and it does not. Any help would be greatly appreciated.
Thank you.
A. The two possibilities are a bad heater control valve or a clogged heater core. I don't remember if it is vacuum operated or mechanically operated but it's easy enough to tell. Just look at the valve, if it has a cable attached to it and it opens and closes the valve when you switch from hot to cold, then it's okay. If it's vacuum operated, then there should be vacuum at the valve when you move the temp selector.
Also, feel the hoses before and after the valve. If they are the same temperature when the selector is in the full hot position, then there is flow through the valve. Then feel the hoses going into and out of the heater core.If the outlet is substantially colder than the inlet, chances are you have a plugged heater core.
If it's vacuum operated and the valve isn't opening, check the vacuum supply line from the intake manifold to the heater control assembly. It may be broken or disconnected.
Additional Information provided courtesy of ALLDATA
