Serving Miata Owners in the Delaware Valley Region
Yesterday my heater worked fine on the Covered Bridge Tour; today after doing a routine coolant change (not a flush - just a drain and fill), I get no heat from the system....AC works fine, fan works fine and the selector switch for the vent positions works fine. I have turned the temp knob CW and CCW several times - still no heat. Is there a possibility that while draining the coolant, some coolant also drained from the heater core and, even with the short test drive I took after the refill, the coolant hasn't circulated in the core to drive out an air bubble??? I checked fuses....there doesn't seem to be a specific fuse for heater operation....I don't have an electrical diagram....is there a relay in the system specifically for temp control? If so, would someone which relay it is?
You may need a simple fix like replacing the radiator's thermostat . I once experienced the same problem after flushing my radiator. It took me a while to find out what the problem was. During a couple of cold winter months I let my wife use the Miata and I used our Camry.
It could also mot be working because the new fluids haven't circulated through the entire system. Or, maybe you didn't add enough fluids to entirely fill the system. Check the fluid level in the overflow reservoir. If it is entirely empty that's likely the problem.