A furnace has many parts that need to be working in order to provide heat for your home. Here is what you know about what could be wrong with the blower motor and the limit switch.

Blower Motor Problems

After the furnace's burner is lit, the blower fan is actually delayed a bit before it starts running. The purpose is for the heat exchanger to warm up because the furnace would otherwise start producing cold air due to having a cold heat exchanger. If the blower motor is broken, then it is not going to kick on at all. 

When troubleshooting the blower motor, you'll need to give it a minute or two for the heat exchanger to get to the proper temperature before you notice that the blower motor turns on. If it is still not working right after several minutes, then you know that the problem could be with the blower motor itself. 

There are a few ways that an HVAC technician can check to see if the blower motor has started to go bad. It mainly involves testing to see if the blower motor is capable of receiving power since it could be an electrical issue that is causing it to fail. They'll try to send power directly to the blower motor to eliminate the motor itself as the problem. If the blower motor powers on, it could be narrowed down to a problem with the control board needing to be replaced, because the signal is not being sent to the blower motor to turn it on.

Limit Switch Problems

The purpose of the limit switch is to monitor the air temperature in the heat exchanger. If it senses that the air is too hot due to the system overheating, the limit switch is going to shut down the furnace to prevent more problems from happening. The heat exchange can overheat due to something as simple as a furnace filter that has not been replaced, which causes restricted airflow in the furnace. More complicated problems will require further troubleshooting though.

If you know that the blower motor is working properly and the furnace has proper airflow with a clean filter, but the furnace is powering off soon after turning on, then you may have a defective limit switch. The limit switch will then need to be tested to ensure that it is working properly. If it is not, then the switch can be replaced with a new one to fix the furnace. 

For more information about furnace repair, contact a local repair service, like Powder  River Heating &  Air Conditioning Inc.