Lennox Air Handler Fan Problems

lehenson · 08-31-2009, 06:12 PM

Hi All,
I have a Lennox 80MGR that is in series with my refrigeration coils and serves as an air-handler. The fan suddenly stopped working yesterday. I obtained a new condenser and replaced the old, and that did not help. I see one red LED on the control circuit board, and it flashes slowly and steadily. I have read on this forum that sometimes the LED flashes a count to signify troubles, but that doesn't seem to apply here.
I would like to bypass the circuit board to see if the fan will run. I could also replace the control board, but if the fan motor is bad, I hate to throw good money after bad!
Any suggestions wouild be appreciated.
Loyd

yuri · 08-31-2009, 09:53 PM

1) Try put the fan on ON at tstat.

2) Try run the heat and see if the fan works (uses a different relay than cooling)

Let us know the results

steady flash is "heartbeat" which means Good.

lehenson · 09-01-2009, 01:06 AM

Thanks Yuri! I really appreciate your response to my cry for help....
I had tried turning the fan on manually with the thermostat "ON" switch and I tried it again just now with NO results. No clicks, no hums, no wind...
Next I went to "Heat" on the thermostat and turned it all the way up (it's about 86 degrees in the house) and I was able to get a light off. The flames burned normally (I think) and I got NO fan. I was about to turn the furnace off again after about a minute, but it shut off the flames by itself. Probably a thermoswitch? Will I need to reset anything to get the heater going again in the winter or does it auto reset after cooling?

Anyway, both tests resulted in NO fan operation. What next, a new fan?

Thanks,
Loyd

yuri · 09-01-2009, 03:47 PM

Are you sure it is not a 80MGF not a MGR? don't think they made a reverse flow R model. Get me the complete model #. Ie:80 MGF-75-3. I need the last number to know which series it is.

lehenson · 09-01-2009, 03:57 PM

WHoops! Typo! Exact and complete model is: 80MGF 4/5-100R-1.
Based on what you told me last night, Yuri, I surmised that since the second relay didn't start the fan that I likely had a bad fan motor. I have just picked up a replacement (it was cheap), and will be wiring it in soon. I'll let you know. Even if that's not it, the fan motor was so much cheaper than a service call.
Loyd

yuri · 09-01-2009, 04:01 PM

You can remove the wire from the cool terminal on the board, label it, and then remove and label the other fan wires. Leave the white neutral wire from the motor on the board. Then hook the cool speed wire up to the main power to the furnace and see if the fan runs. May be a bad circuit board.

lehenson · 09-01-2009, 06:25 PM

Yuri,
I have already removed the old fan motor. Might I gain any good knowledge by leaving the motor out but turning on the power and doing a voltage check at the COOL connector on the board. It should have full voltage at the connector when the T-Stat is calling for cooling, no?
Loyd

yuri · 09-01-2009, 07:05 PM

Yes it should. You can also rig up a extension cord and plug the motor into it with white wire as neutral and capacitor hooked up.