Hello,

Hoping someone can help, we’ve had issues with our furnace, it’s a W96T WeatherKing, the furnace is stuck on Cool Mode. When it boots up, it automatically registers a “C” and activates the fan, condenser, etc when the thermostat is set to heat.

This is a condition that remains after we had to replace a faulty motherboard. So we’ve since replaced the wiring from the thermostat to the furnace to rule that out.

I’ve had to disconnect the A/C wiring so the condenser isn’t running 24/7, but the fan still runs cause it thinks it’s cooling. I’ve even tried to disconnect the Y wire and the furnace won’t function cause the board is trying to activate the C code, but can’t without the Y wire connected.

Are there any ideas what other wiring or devices on the furnace I should check or replace that might be causing this strange problem?

Thanks so much in advance.

 

Sorry... that doesn't make any sense.
What does registers a C mean ?

I cannot get a grasp on your problem.
Usually it's easier if you just say what's happening with no terminology.

I see a gas furnace and am assuming a standard split A/C...... no heat pump.

 

Sorry…. not very experienced at this forum stuff yet.

It is a gas furnace, 2 stage heat, with a split AC unit. There is no heat pump. The C code according to the index is that the unit is calling for cooling.

So the board shows a C when cooling and a H while heating. Upon boot up it jumps right into C, fan starts up, and before I disconnected the split AC, the outdoor unit started up and I could hear the AC lines feeding the coil.

I’m just struggling to understand what is causing the board to call for Cooling mode if it’s not the thermostat.

This has left technicians stumped, so I’m reaching out with some hope that someone might know what other condition would cause the board to enter call for cool, if it’s not the thermostat…

The furnace blows cold air and AC runs when the thermostat is set to “off” or “heat”.

 

Test on the low voltage terminal block with your meter. Are you getting an active cooling call there? If so it’s the thermostat/thermostat wire.
Are you using a Nest thermostat?

 

thanks Roughneck, we are using a Nest. I disconnected the wires that run to the AC unit and it still calls for AC. Last night I disconnected the black wire to Y on the board, and now the code on the board is “0” which is the normal standby code when there is no call for heat or cool (furnace is now functioning normally for heat only). So I’m guessing that it has to be an issue with the Nest, cause we just re-pulled a new 6 conductor yesterday.

It’s a Nest E

 

Pulls the nest off the wall, disconnect all wires from it and see if the issue still exists.
The nest has proven to be extremely unreliable and the cause of many equipment breakdowns. I’ve charged customers tens of thousands of dollars in total to pull them off the wall and throw them away.
I wouldn’t have one if you paid me to use it.

 

I see, okay - thank you.

so since I d/c the Y1 and the issue went away, it’s likely the thermostat then.

I wasn’t sure if the control was at the board or downstream of the board that calls for cooling. Thought maybe a switch was faulty and stuck in open position or something.

are ecobee thermostats better? Or just got back to a Honeywell.

 

You need to verify. Pull all the wires off the Nest and verify the issue goes away.
Honeywell and Ecobee have superior products.

 

Cheers Roughneck!

I connected the Y wire on the furnace panel, then pulled the Y wire from the Nest, powered furnace back on and the issue went away.

Guess I’m going shopping?

 

Yup.
Landfills and recycling centers are getting full of faulty Nest products.

 

Try removing the wire at O/B. That"s used with a heat pump.

 

Good point on the O/B wire.

That board comes back to a Rheem/Ruud product however the specified board is different than yours. It shows a board with five terminals. Yours has six.
Can you tell us what letter is next to each wire ?

white -
blue -
green -
black -
orange -
red -

 

So the O/B on this particular Nest can be programmed as Heat Pump or Secondary Heat or Cooling. Since the furnace is a two stage; it is wired to the W2.

my connections are:

black : Y1
green: G
red: R
white: W1
orange: C
blue: W2

A government promotion supplied this Nest free of charge, and they took the old one with them, wish they didn’t so I could test the connections on the old thermostat.

with the black wire unplugged, both stages of heat work normally, fan is only turning on during call for heat (auto) so all is good until the day comes for AC, so I guess I have some time to shop for a deal and hope that the issue is indeed the Nest erroneously calling for Cooling when cool is set to off on the Nest screen.