Have a 2004/5 Comfortmaker furnace/air unit. Blower cycles on and off while furnace is fired up. Also cycles when furnace is turned off and fan on thermostat is turned to "On" (as opposed to "Auto"). No fault codes are flashing on the control unit. Some condensation on the exhaust piping. Problem has cropped up in the midst of recent cold snap. Filter is clear. Vacuum tubes in unit are clear. Thoughts?

... again, the furnace/flame works fine and stays on. It's only the blower. Thanks!

You need to check for 120 volts between the fan motor terminal on the control board & neutral or gound while the blower is acting up. If you are losing power, I'd say it's a bad board. If 120 volts is consistent, it's likely a motor problem.

Thanks Grady! Replaced motherboard. Worked all day yesterday. Woke up to same issue. Thoughts?

I doubt there is any kind of low temperature contol for the fan. I'm sure it's all timed. With the fan motor cycling on & off, check the motor to see if it is hot. If so, it could be the motor or as simple & inexpensive as a capacitor.

Motor tests OK. On this model, there is a separate control unit for the blower. It appears be functioning improperly. There are several large capacitors in it. Unfortunately, comfortmaker no longer makes the control unit separately. It is only sold w the blower ($1200) AND is not avail until Jan 16. Not sure I am qualified to mess w the caps in the unit...

Never seen such. Can you take & post a photo?