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davegardner0 03-06-2013 01:09 PM

Lennox AM30 CompleteHeat Blower Problem
I recently purchased a house with a Lennox Complete Heat natural gas heating and cooling system. I've heard this system isn't the best, but so far it has been working. I think it is 13 years old.

Last night, I noticed that the heat exchanger (AM30) in my attic was no longer blowing air. The water circulator pump was pumping water through the heat exchanger, but the fan wasn't working at all. I took a look inside the unit, and tried turning it on with the cover off, while testing things with a multimeter.

The relay that switches on the fan was closing the circuit when it should be, but the relay had no voltage across it. I tried this for both the heat and fan-only settings, since they use separate relays. Neither worked.

I suspected either the motor or something electronic had failed, since it smelled like burned electronics inside the unit. I disconnected the wires and took the board out, and noticed that the board was burned through right behind the first relay, and possibly also behind the black box above the relay (maybe a solid-state relay for the circulator pump?). (see my photo link below)

I have a new circuit board coming, but I want to make sure there wasn't some external cause for this failure, that will burn out a new board, too. I'm thinking too much current flowed through the relay, for some reason. Maybe an issue with the motor?

I measured the resistance across each of the leads of the blower motor and the ground, and measured 3.2 Ohms, 4.4 Ohms, and 6.8 Ohms. Is this normal? I'm thinking I can connect the motor directly to the 120 VAC power in temporarily to test it further. What else can I do? It has some big capacitors connected to it - could those be the culprit? If so, how do I test?

Is there anything else I can test?

Here is a link to some photos I took while disassembling:

Thank you in advance for the help!

davegardner0 03-08-2013 07:31 AM

I took the motor apart, to see if there were any problems there. Nothing jumped out at me. The sleeve bearings have a felt material that holds their oil. The felt was deteriorating a bit and falling out. Maybe the bearings aren't getting enough oil and are heating and binding as the fan runs.

I put the motor back together and ran it for about 30 seconds - everything seemed fine. The next test I'm thinking of is to run it for a while longer and see if anything heats up.

A new board from eBay is coming today.

Any other thoughts of things I can test. I'd like to find the reason that relay blew up (if there is one) before I put in the new board and have it suffer the same fate.

yuri 03-08-2013 12:25 PM

the relays blow on them just from old age/usage. I would never buys parts from zbay as they could be used etc. for good Lennox parts.

davegardner0 03-08-2013 12:48 PM

yeah I know I'm taking a risk with ebay. But, I've been told the whole system doesn't have much more life in it, and I'm thinking of a replacement this summer. I couldn't justify $200 on cozyparts vs $30 on ebay since this is a temporary fix.

That's good information, though, about the relay failing on its own. Thanks!

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