Problem: I have Rheem furnace/ac unit, in the winter when it is in the heat mode I’ve noticed a howling sound ( the last couple of years) coming from one of the ducts. I looked online but can’t find a resolution. The sound is not present when in the A/C mode everything sounds normal. Might you have any suggestions.
Answer:The only things that I can think of that might cause a howling sound would be (1) Return registers sometimes cause a howling sound when too much air is trying to be drawn through the register. I would suggest making sure all the returns are clean and not obstructed. You might try taking off one of the registers off and see if the howling stops. I have had this howling happen to me before when I installed a new furnace with a larger blower. Too much air was being drawn through the returns and it sounded awful. I had to install another return to eliminate the problem. Since your noise occurs in the winter time it probably is not a return air problem because the motor pulls more air in the AC mode and less air in heating mode. So the too much air theory is probably out. (2) Another problem might be a blower motor that has a weak run capacitor. In the winter time the blower motor runs on a lower speed. If the capacitor is weak and the motor is running in heating mode at low speed then this will cause a howling sound in the motor. You might want to have your blower motor capacitor tested. Sometimes small appliance parts stores will test capacitors free of charge. (3) another cause of howling might be too much gas pressure if you have a gas furnace or a stopped up gas orifice. I would suggest seeing if the noise is only present when the gas is on or not. If the furnace is howling when the gas is on then you might need to adjust the gas pressure of clean out the gas orifices. That is about all I can think might cause the problem. I hope you can find the problem I hope that you have a great day!
Steve Arnold, https://arnoldservice.com