Attic Fan Does Not Run On High Speed

High speed and low speed.

Attic fan does not run on high speed.

Then after checking the capacitor for a short or an open measure its value. If the attic fan isn t turning on it could be an electrical issue a problem with the thermostat or the motor of the fan that s not working. Running the fan when the air conditioner is not on could actually pull the heat out of the attic into the home. Check motor current draw and compare with specs.

Check that the blade moves freely. Most of those attic fan motors have two motor windings. You select which speed it runs at based on the switch position. If it is rotating slowly or not producing a lot of air in the high speed setting you may have a problem with the exhaust or intake.

Parts can come loose or erode from high amounts of fan usage while turning the speed up to high can cause a persistent loud hum. If you have leaky ductwork. If there is any damage to the belt replace it with a new one. Attic fans can sometimes start making noise whether it s humming rattling or making some other annoying noise.

Little or no airflow. Your attic fan may not be turning on because of an electrical problem like a tripped circuit breaker a blown fuse or a bad connection. I ve never heard of one that starts on high and switches to low. When running at a high speed setting does the attic fan run hard or sluggishly.

Attic fan not turning on. For this you can use a 9 v battery a dvm and a 1 megohm resistor from radio shack. You can fix this issue by turning down the settings or checking that the fan is getting enough air. Some info on the motor is needed.

Unfortunately homes built before 2015 may have very leaky ducts.