[Ginn7]

Hello,

Last summer my A/C was working fine with no issues. Come fall we had a blower motor issue with our furnace and had a tech out to replace it. The furnace worked fine. Now this year with the warm weather I turned on the A/C but it did not turn on, more specifically the outside unit does not turn on. The thermostat says cool, it clicks, but the outside unit does not do a thing (not even a hum).

I checked the breaker, outside disconnect, and I even checked for power to the outside unit (all seem ok). Now I figure that there must be a problem from the thermostat communicating with the unit (somehow the signal is not getting to the control board or from the control board to the unit.

I opened the furnace door to take a look at the control panel. I found two things (see attached pic). First there is label A, this is the black/white wires going to the outside A/C unit, as you can see they are not connected to anything. When I check them for power they have a current. When I turn off the A/C breaker the power is gone. My first question is: shouldn't these be connected to something on the control board? Second is label B, you cannot see the end of the black wire here but it is also hanging loosely not attached to anything.

I do not know if the last service tech disconnected these wires but the A/C was working fine before he came to fix the furnace. I did not test the A/C after he left because it was November so there was no need. Maybe he forgot to reattach them or did it for some other reason. I just want to know if these wires should be attached to somewhere on the board because it would explain the issue before I call someone in to fix it.

 

[Ginn7]

EDIT: It seems the black wire I indicated was hanging loose in Label B is attached to a transformer. Like I said it is hanging loose on the end you cannot see in the picture, just an exposed braided wire tip. The other three wires from the transformer (2 white and another black) are connected.

 

[user_12345a]

When I check them for power they have a current.

What do you mean they have current?
How did you check for power?

If they have voltage only with the outdoor unit's power on, it may have it's own transformer and it's being switched by a relay.

The black box is a relay, not a transformer.

To know for sure, the wiring inside and outside would need to be traced.

 

[Ginn7]

I did not use anything fancy just a voltage sensor that beeps if their is power to in a wire or outlet. I'm not experienced with voltage or measuring it. When the breaker is on it beeps when I touch the wires (Labeled A), when the breaker is off there is no beeping. I'm thinking this may just be residual power it is getting from the unit because I can't see why they would carry any power but 24V to the unit.

The black and white wires in label A go straight to the outside unit, from what I can see these are the thermostat wires that tell the outside unit to turn on. But how can they do that when they are not connected to the control board? So they must go on one of the terminals (eg. Y, C, or another one). The Label B black wire coming from the 'relay' needs to be connected to something as well I'm guessing.

 

[Ginn7]

Here is a picture that might help. Label C is the black/white wires (Label A) coming from the inside the furnace out to the outside unit. The black cable goes to the connection in (Label D). The white wire is connected to a yellow/red stripe wire with a marett and it leads to somewhere inside the unit (Label E).

Hope this helps.

 

[user_12345a]

For some reason there's a relay - right now Y and C are wired to the relay and presumably that switches the a/c on and off. I'm unsure of why the relay is there - could be particular to that model furnace but i doubt it.

Trace all the wires connected to that relay. Take a pic of the front of the relay, zoomed in so i can see the diagram on it. (fully - try to push wires out of way)

or get the model off the relay and i'll look it up.

 

[Ginn7]

The 1 label white connects to a black wire which goes the the Y terminal on the upstairs thermostat. The labeled 2 white wire connects to C on the board. The 3 label black wire connects to Y on the board. The 4 label back wire connects to nothing (it is hanging loose.)

There is no label on the relay (I drew in the part in the shadow if it helps).

 

[Ginn7]

BTW, here is a another picture of the relay and the hanging wire.

 

[57TinkerMan]

I don't know why you would have an isolation (if that's what it is) relay in there. I would pull it out and wire it like the picture below. Keep it simple. Drawing wire colors and your actual colors are different. Focus on the proper terminal connections.

 

[Ginn7]

All I need to do it seems is re-connect these wires to the proper terminals on the board.

For simplicity, in my case with the relay left in where would I attach the white wire and the black wires from the outside ac unit on the terminals? And would I need to connect the hanging relay wire, if so where.

BTW, I do not have anything connected to C in my upstairs thermostat (see picture below).

 

[57TinkerMan]

Drawing is generic, don't worry about a C wire from the stat. Easiest to just eliminate the relay, it serves no purpose that I can see. You can leave the relay in place if you want, just hook up wires as shown.

 

[57TinkerMan]

If you really feel you must have the relay in play.
Dangling wire goes to R terminal.
Black to outdoor unit to Y terminal.
White to outdoor unit to C terminal.

 

[Ginn7]

EDIT: Sorry I sent this before right after you answered my question.

 

[57TinkerMan]

Doesn't matter, AC volts, either way will work.

 

[Ginn7]

Do I really need to connect the relay to R at all? Will it hurt to leave the wire off and just connect the black and white wires?

 

[57TinkerMan]

Yes, the way the relay is wired the loose black wire has to be connected to the R terminal, your outdoor unit would not get 24V if you don't.


Edit: because you don't have a C wire from the thermostat you should change the battery in the thermostat while doing all this stuff.

 

[Ginn7]

Thanks 57TinkerMan! and user_12345a for your help.

The fix worked and my A/C is back up and running. It will be a much more pleasant sleep this evening.