Problem: Outdoor air conditioning unit is running but the indoor furnace blower will not run with the fan in the “Auto” position on the thermostat and the thermostat calling for cooling.
Answer: This could either be the thermostat, thermostat wiring (loose or broken wire), blower motor capacitor, blower motor, control board or fan center that is causing the fan on the furnace to not come on and run.
- I would start by checking the thermostat. Check with a volt meter between the G (green) and C (com) terminals with the fan in the auto position and with the thermostat calling for cooling. (You might have to tape the blower door safety switch closed to do the testing) Please be careful to not get shocked. You should get 24 to 28 volts between the G & C terminals. If you do not then you either have a thermostat problem or a thermostat wire problem.
- If the G & C (com) check out OK then go to the terminals that provide power to the blower motor and see if you are getting 110 to 125 volts to the blower motor. On the control board you would test between the terminal that is connected to the “Cool” terminal and any one of the neutral terminals. You should be able to see the wires that go to the blower motor. If you are getting 110 to 125 volts to the blower motor then the control board is OK and probably the blower motor is bad or the capacitor is weak or bad.
- If you do not have a capacitor tester then I would suggest taking the capacitor to an appliance parts place and see if they will test it for you. Please click here if you would like to see the capacitor tester we sell.
- On older furnaces many times the fan is controlled with a fan center. Below we have a YouTube video made by grayfurnaceman that shows how to troubleshoot a fan center. Thanks to grayfurnaceman for making this informative video! We sell fan centers on the following page: Please click here to see the fan center we sell. We sell fan blower motors and air handler motors on the following page: Please click here if you would like to see the OEM blower motors and air handler motors we sell. We sell many different OEM blower motors. It is always easier to replace a motor using an OEM motor instead of a universal motor because the wiring and everything matches up with an OEM motor. We also have a YouTube video made by MagicPatrick1 that shows how to troubleshoot and replace a blower motor. Thanks so much MagicPatrick1 for making this informative video. If you have any questions please email us at: firstname.lastname@example.org or comment in the comments section below. Thanks! We would love to help you out and have your business! Steve Arnold