[DangNotAgain]

Trane Split System 2TTR3036A1000A, 2 yrs old

Hi.

The furnace works fine. But when set to cool, neither the air handler or the compressor operate. Also, the "fan only" setting does not run the fan.

I checked the 2 A slow-blow fuse on the board, and it's fine, but I assume that the furnace wouldn't operate if that was blown, anyway.

On the T-stat, I shorted Y to Rc, but no response.

The only thing I can think of is to check continuity between the T-stat and the furnace. Any other ideas?

Thanks.

[Joshdta]

Check to see if you have 24 volts between c and y at your control board with the t-stat calling for cooling.

[Joshdta]

If so then check to see if ou have 24 volts outside at the ac unit

[DangNotAgain]

Thanks for the help.

There is no voltage at all between Y and C (to clarify for others, this would be AC voltage).

[Joshdta]

If you have no volts between y and c at the control board then the t-sta must be bad. Take it off the wall and jump between y and r and see if the ac runs

[DangNotAgain]

I had previously jumped Y and Rc, according to the t-stat troubleshoot sequence, but nothing happened. I re-read the guide, and it says that for a 4-wire system (like mine), R and Rc should be jumpered. It's not jumpered. So, I jumped them, and the A/C started.

That's strange, because it worked last season. I don't see how a jumper (and screw) for Rc could have gone missing over the winter. I never removed the T-stat, and there's no evidence of a screw or jumper wire. So, I don't know if the jumper was ever there. Anyway, under the assumption that it was, I guess I'll go get a proper fitting screw and put in a jumper.

Correct action?

[Joshdta]

Yep sounds like you have it figured out. Very odd though indeed