Uploaded January 2010 | Updated September 2026, 3 hours ago
Fluctuating RPM of Variable-speed Motor Problem In Air Handler - This creates CFM balance problems and an air rushing noise in the ductwork. The controller appears to be "hunting" for the proper speed signal to send the motor. This is a video of one of the heat vent registers with a piece of paper taped to the top so you can see the RPM and CFM airflow variations more clearly. This video was made three minutes prior to the heatpump cycling off.
Timeline:
12:03 pm - Raised the temperature on the thermostat by 1 degree.
12:03pm - Fan starts out on low speed
12:04pm - Fan speed increases to a medium speed
12:12pm - Fan speed increases to a high speed
12:23pm - RPM FLUCTUATIONS BEGIN (last about 3 minutes)
12:26pm - Fan turns off
The problem turned out to be a stray voltage in the 24VDC thermostat. The thermostat was replaced and the system is now operating normally. Good job guys!
Fluctuating RPM of Variable-speed Motor Problem In Air Handler - This creates CFM balance problems and an air rushing noise in the ductwork. The controller appears to be "hunting" for the proper speed signal to send the motor. This is a video of one of the heat vent registers with a piece of paper taped to the top so you can see the RPM and CFM airflow variations more clearly. This video was made three minutes prior to the heatpump cycling off.
Timeline:
12:03 pm - Raised the temperature on the thermostat by 1 degree.
12:03pm - Fan starts out on low speed
12:04pm - Fan speed increases to a medium speed
12:12pm - Fan speed increases to a high speed
12:23pm - RPM FLUCTUATIONS BEGIN (last about 3 minutes)
12:26pm - Fan turns off
The problem turned out to be a stray voltage in the 24VDC thermostat. The thermostat was replaced and the system is now operating normally. Good job guys!
