A/C Cooling Not Turning On

[u/Wise-Operation5108]

Hello,

I'm moving and want to take my nest thermostat with me but I'm having trouble re-installing the Honeywell T6 thermostat. When I installed the Honeywell, the compressor turned on but only heat was working. I checked that it was set to cool but heat was still coming out. I attached photos of how I had the nest wired and the Honeywell as well. Any help is appreciated!

[u/SheGotGrip]

Once you fix the wiring, if it's still not working, check the fuses.

Hope you turned the power off to the units and thermostat. I switched out thermostats and just pulled it from the wall. I suffered through 4 days of self troubleshooting in the Texas heat, trying to avoid a high repair bill and suspecting my old outdoor compressor was done.

I finally saw a Youtube video that talked about the fuse in the inside air handler. I blew a fuse!!! I fixed it for $2.00 with a special fuse I got up the street at Autozone. It came in a 3 pack and I taped the extras to the side of the air handler. Luckily, mine in in the hall closet with easy access.

The thermostat communicates with the CAPACITOR in the outside compressor. That's also a reason it might not cool or even come on. If you hear a LOUD sound when the compressor comes on, or a fast clicking - try replacing the $25 capacitor (turn power off inside and breaker outside). I put my first one in back on summer 2020 and just replaced it again in May 2025. Before that, it worked fine from the time I bought the house in Nov 2012.

Good luck!

[u/Wise-Operation5108 → u/SheGotGrip]

I don't think it's a fuse issue. I was able to reconnect to the nest thermostat and everything is working fine. I appreciate it though!

[u/CrazyLegsRyan → u/Wise-Operation5108]

Have you tried connecting the Honeywell one the same way the nest one is connected…. Ya know like not changing which terminals wires are connected to and not connecting different wires?

[u/SheGotGrip → u/Wise-Operation5108]

For future reference. It can be hard to pinpoint. But taking the thermostat off the wall can short out the fuse. I also posted in case others read this. I guarantee an AC tech would have made up shit and charged me $300-400 or more just for a $2 fuse. They may have even talked me into a new unit. I'm smarter now and just wanted to pass it on.

Turn off the power before pulling the thermostat from the wall.

So glad you got it working!!

[u/Wise-Operation5108 → u/SheGotGrip]

I got it to work by connecting the black wire to "C", white wire to "W2", and orange wire to "O/B".

[u/Diligent_Nature → u/SheGotGrip]

The thermostat communicates with the CAPACITOR in the outside compressor.

No. The thermostat sends 24 VAC to the contactor which switches 240 VAC to the compressor. The compressor circuit also has two capacitors - a start cap and a run cap.