My furnace is overheating and I suspect that the blower motor does not go into high speed. Can anybody say what is the cause or how can I check if it indeed switches to high speed?
Here is the wiring diagram
and here are the specs. This sticker shows that it has a second speed. I suspect that switching to that second speed is not happening
the furnace is hotter in the areas marked on this picture. I suspect it might be either the blower at reduced speed or the heat exchanger that is cracked
Best Answer
Most furnaces; yours included it appears, do not change the speed of the motor during normal operation. The motor typically has three or more speeds (high, medium, and low), and is hard wired to use different speeds based on what mode the furnace is in.
For example, in heating mode most blowers run at low or medium speed. While in fan or A/C mode, they run at high speed.
If your furnace is overheating, the first thing to do is to make sure the filter(s) are clean. Also make sure all the registers and returns are fully open, and unobstructed.
If you haven't checked already, check the temperature of the furnace when the limit trips. You could have a bad limit, that is tripping when the furnace is not actually overheated.