the heater/blower only works sometimes, usually not at all when it’s freezing out. when it’s a little warmer out, it tends to work more often, but still not all the time. what could this be? my husband tried replacing the blower motor, but that didn’t change the situation, so he put the old one back in, and is now puzzled ?
Well, the blower cage bearings could be toast I suppose. The motor turns the cage, but if the cage won’t turn, a new motor won’t change things. In fact there’s a chance of ruining the new motor if the cage won’t turn freely. Sometimes the cage bearings are ok, but leaves and stick in the works are the problem. And it could be that the motor and cage are fine, but the switch or relay in the circuit is failing. Ask your mechanic to check through all those items one by one.
You need to check the switch. The most straightforward thing is to put a voltmeter on the blower feed plug it when it isn’t working. If voltage is coming through, the plug contacts should also be cleaned and inspected. The female side can get loose and lose it’s “springiness.” If it does it would act up more when cold.
The problem might be with the vent control module.
Solid state circuit boards can be effected by the temperature.