Hello!
I have an old central AC unit that cools the house but has to be switched on and off from the breaker. As soon as the breaker is switched on, regardless of whether the thermostat is set to heat, cool or off, the condenser comes on. The only way to turn it off is by switching it off again at the breaker. It appears to be wired to the furnace and those wires are then connected to the thermostat, but it just seems to not be "speaking" to the condenser. I've included pictures of the furnace control board and the thermostat wiring. The furnace is a Lennox Elite Series. Thanks for any help you can provide. Lennox Control Board Noma thermostat Lennox wiring diagram: one thing I do notice here is there appears to be a common wire that runs from the control board to the thermostat that my system does not have. Not sure if that's part of the problem.
Actually, yes I did replace it with a Nest. I forgot to mention that in the original post. I copied the wiring from the Noma thermostat but even with the nest it still doesn't seem to control the condenser. Here's a pic of the nest wiring: Nest wiring
Thanks for the reply roughneck77. Not sure what you mean by welded. Do you mean he might have welded something at the condenser?
Were you having this problem before you changed the Stat? as for the welded contactor open the cover in the control area on the condenser, the contactor will have some large wires on it, be sure the power is turned off to both air handler and condenser and see if that part of the contractor moves freely in and out.
post a pic of what you have there and we can point you in the right direction.
another thing you can try is to remove the 2 wires from the Y terminal on that control board and see what happens then.
Geo
Yes this behavior was happening before. We bought the house about a year ago and the owner wasn't willing to fix it. I'll try your suggestions and post back with pics in a few hours. Thanks again!
Hi, this link will give you idea of what the contactor looks like, it may or may not have a cover on it, if it does remove the 2 small screws on the front, also one other thing to try is remove one of the small on the side of it and see if that makes a difference. https://www.homedepot.com/p/Noark-40...20G7/300813144
Contactor is in the condenser. they can weld closed and cause symptoms such as what you have.
That nest will need a common wire. Not having one can cause an already unreliable thermostat to perform more poorly then it already does. I’d suggest removing it and instead using a product from Honeywell or Ecobee.
The picture shows rectangular pipe carrying hot or cold air from the heater or AC. There is a shutter inside the pipe that can be rotated to adjust the amount of air going from the left (source) to the right (2nd floor). When the shutter is positioned vertically, there's no flow to the right while the passage is completely open when the shutter is positioned horizontally. The problem is that the horizontal position of the shutter is very unstable and it tends to move to be very close to vertical when left to itself.
So what you see in the picture is my clumsy solution to keep the shutter in place - an adjustable wrench tightened on the shutter axis and taped to the pipe wall. Is there anything better that can be done, short of taking everything apart?
06-30-20, 02:47 AM
