HVAC tech in chit chat

[Paragon]

My main unit HVAC is a Lennox G40UH. It keeps cutting off and won't come back on. No A/C, no fan, no heat. The 2 green LEDs won't light up. Tech has been out here.

He soldered something on the control board one time. I discovered the door switch wasn't working and wired that switch out of the circuit.

now, when I plug the unit in I can hear a relay click but nothing happens. if I turn off the electrostatic filter and the humidifier and plug in it/out quickly a couple of times to fool the relay I can the unit to stay on. tech says it's control board and they are back ordered

I think it's the transformer because of how it acts.

Also, I just spent a while up there fucking with this thing and it's like 142 degrees and 199% humidity

 

[yozsi]

Can you wire the contactor to come on when the thermostat calls for ac? Just completely bypass the electronics and run the blower on high speed. Just do it temporary until you get a new board.

 

[Paragon]

Can you wire the contactor to come on when the thermostat calls for ac? Just completely bypass the electronics and run the blower on high speed. Just do it temporary until you get a new board.

If I can, I don't know how. I have it cooling right now. I might google that if it does it again before dude gets out here with a new board

 

[Paragon]

it sounds like a safety is tripped not letting the unit kick on. Door safety could be it. Can you google all the safety circuits for that unit and just jump each of them out?

EDIT: to add, due to covid, all the lead times at all the factories are super long right now. So you better hope its not that. Might as well just buy a new unit.

I straight up cut the door switch out. Cut the wires and spliced them together.

When I plug it in I can hear a relay click and a relay or something is slightly vibrating when it plugged in but not working. I find it odd that I remove the humidifier and electronic filter shit from turning on, that it will then turn on. That is what had me thinking it was the transformer vs a bad board

 

[Paragon]

I have figured out that a soldered joint where a multi-pinned plug plugs in must be fubared. I can flex that plug and hear the relay hum a little louder. If I unplug the 120v and plug back in while flexing the control board at that plug, voila, it starts

 

[Johann]

I have figured out that a soldered joint where a multi-pinned plug plugs in must be fubared. I can flex that plug and hear the relay hum a little louder. If I unplug the 120v and plug back in while flexing the control board at that plug, voila, it starts

Cold solder joint or one of the traces is compromised? Or is it the actual multi pin?

 

[Bowe]

It's somewhat common to find cracked solder joints on those molex plugs. Also on the joints for the thermostat connections.

 

[GM Guy]

After watching the guy who installed my furnace, I'm not surprised there are circuit board problems. Its like hvac people have no concept of supporting a board they are trying to plug in a tight fitting connector. Though, just as much blame to the manufacturer for not appropriately placing standoffs.. Of course, they won't sell as many boards due to lack of installer induced cracks that eventually lead to failure. Pull the board and resolder it.

 

[trampas]

It's somewhat common to find cracked solder joints on those molex plugs.

This

 

[Paragon]

Cold solder joint or one of the traces is compromised? Or is it the actual multi pin?

Solder, I’m pretty sure. I even know which pin, since it looks it’s the pin the dude soldered before. I guess he didn’t want to admit the problem was the same that he supposedly fixed before.

I pulled the panel off the mounts to see what was happening behind that plug and saw that was where he soldered before