[hotorcold]

Hi guys, have an odd issue that i'm trying to troubleshoot on a Sunday and wanted to get some advice. Unit is an older (14-16 year old Lennox)

I have a thermostat downstairs that I thought was going bad...would power cycle just as soon as the air kicked on so I thought its just shot because its one of those wifi ones with the backlit screen. Got a spare one to try out...same thing. So I did a little checking on the unit itself.

When I look at the saved error codes I see : 9, 3, 2, 2, 8

So I thought maybe its the pressure switch. I got a spare and swapped them out, same thing. Checked wiring, nothing looks out of order. Board was replaced about a year ago so I don't see much wrong there. Something is killing the power though.
When I watch the board itself, I have the green light steady blinking (normal operation) the entire time. I hear the fan kick in, goes for maybe 15 seconds then turns off...thermostat cycles power immediately as soon as it calls for cool air. Something is triggering the system to quit. Any thoughts?

 

[user_12345a]

Is your stat a nest and if yes, is the common connected?

Can you give the full furnace model number? Usually starts with a G for a older lennox unit.

 

[hotorcold]

Sorry for the delay, I found a spare control board and was tinkering with that...problem isn't the board either.

Model Number says : P2MPD16N06401C

 

[user_12345a]

The model number suggests it's york, not lennox.

reset the board by cutting and reapplying power, disconnect the stat and jumper R and W.

push in door safety switch and see if furnace operates. if it throws an error code, check schematic to interpret it.

do you have a meter and know how to use it?

 

[Missouri Bound]

Can you measure the output of the control transformer when the HVAC kicks in?
Does it drop when the fan starts or when another contractor pulls in?

 

[hotorcold]

You are correct. It IS a York...it looks like the cover panel has a Lennox sticker on it but everything inside suggests its a York.

I do have a meter, will check a few things including the transformer output and report back

Thanks for the suggestions guys

 

[hotorcold]

Multimeter isn't working, i'll let you guys know the voltage outcome tomorrow when I pickup another one.

 

[hotorcold]

Just to post a resolution in case anyone else runs into this problem. The contactor on the outside condenser had a short in it...it was causing the problem. Contactor replaced, everything started working again.

 

[Missouri Bound]

Contactor replaced, everything started working again.

:thumbup: