Attic Fan Does Not Run On High Speed

Little or no airflow.

Attic fan does not run on high speed.

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. Then after checking the capacitor for a short or an open measure its value. 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. You can fix this issue by turning down the settings or checking that the fan is getting enough air.

Check that the blade moves freely. I ve never heard of one that starts on high and switches to low. If there is any damage to the belt replace it with a new one. For this you can use a 9 v battery a dvm and a 1 megohm resistor from radio shack.

If you have leaky ductwork. Most of those attic fan motors have two motor windings. Unfortunately homes built before 2015 may have very leaky ducts. Attic fans can sometimes start making noise whether it s humming rattling or making some other annoying noise.

Remove the outer casing of the attic fan and check to see if the belt is sagging cracked worn or broken. You select which speed it runs at based on the switch position. Check motor current draw and compare with specs. When running at a high speed setting does the attic fan run hard or sluggishly.

Attic fan not running at top speed. 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. High speed and low speed. Some info on the motor is needed.

Homes built after 2015 are required to have all ductwork sealed and tested for airtightness.