lennox G20Q2E-50-2,blows 2 amp fuse

[vapourman]

I have a Lennox G20Q2E that appeared dead. The 2 amp glass fuse was blown. I replaced it and the fuse remained good with no call for heat. Stat called for heat and the electric damper started to open then the fuse blew and the wall stat started to smell of smoke. I dont see many Lennox products and have seen none with a motorized damper. Is the relay board causing the fuse to blow or is one of the devices hooked to it loading it down? Why did the stat heat up so fast? Why does this natural draft unit have a motorized damper? thanks for any help!!!

[coolwhip]

You have a short somewhere on the 24vac side.

[amd]

Lennox used a motorized damper to get away with selling a conventional furnace as a mid efficiency unit. (rated efficiency - 78% AFUE)

[t527ed]

better call for service before anything else lets the smoke out

[Milk man]

seen a lot of theese units with bad heat exchangers. Could still be under warranty for the heat exchanger only.

[t527ed]

Originally posted by lynn rodenmayer
seen a lot of theese units with bad heat exchangers. Could still be under warranty for the heat exchanger only.

never saw bad heat exchanger on small one like this. never saw bad heat exchanger blow fuse either.LOL

[vapourman]

thanks for you input. I have isolated the board but the fuse still blows with a flash of a dead short even tho I checked every wire in the furnace and disconnected all the stat wires. The fuse protects the 24 volt supply but only blows when the R and W is jumpered. The relays switch the 120 volt devices so they should not be causing any trouble. Can the board fail internally in a way that it only pops the fuse when R W make? Does the relay board have a history of this on the lennox?

[tinknocker service tech]

it could be the board. i tend to think there is a short to ground on w

[wayner211]

It most likely is a short on the 24V side. Some of those are difficult to find and can take quite a bit of time. You might also check to see if the damper is getting stuck and the motor is pulling high amperage. That probably isn't the case but I would still check it.

[vapourman]

the damper motor is 120 volt switched from a relay so it shouldnt load the 24 volt supply. The fuse pops so fast that its got to be a virtually dead short. But there are no dead or low ohms readings anywhere. thanks for the feedback. May have to get the board.

[Milk man]

Originally posted by t527ed

Originally posted by lynn rodenmayer
seen a lot of theese units with bad heat exchangers. Could still be under warranty for the heat exchanger only.

never saw bad heat exchanger on small one like this. never saw bad heat exchanger blow fuse either.LOL

First thing I'd do on this service call is inspect the heat exchanger. Just because you haven't found many cracks doesn't mean they weren't there. Read into that anything you want.

Then if the heat exchanger was good, I'd look for the short.

First things first.

[vapourman]

thanks for the help. unit has been scrapped due to age and low efficiency. never did find the short, removed all wires in and out of board, must have been the board

[t527ed]

Originally posted by vapourman
thanks for the help. unit has been scrapped due to age and low efficiency. never did find the short, removed all wires in and out of board, must have been the board

what replaced it??

[vapourman]

the guy is shopping for another unit now. wants a mid or high. dont know what brand he will go with. I dont install just repair. this is only the second lennox i have seen with a motorized damper door and the other one had been removed and the switch shorted out. soooo guess they are slowly goin in the dumpster