Hi,

I am trying to install a HoneyWell RTH230 programmable thermostat to replace our old Honeywell round thermostat. I have a Miller gas furnace and electrical central air. The wiring to the old thermostat was as follows:

Red
Orange
White
Yellow
Green

There were also blue and black wires coming out of the wall but not hooked up to the thermostat.

I hooked up the new thermostat as follows:

Red to Rh
Orange to Rc
Yellow to Y
Green to G
White to W

And left the blue and the black ones unattached. The heat seems to be working fine but I cannot get the AC to come on? Any ideas?

Thanks for your help.

Disconnect the orange and put a jumper between rh &rc you should be fine ac should work

If that doesn't work, check what the orange is connected to at the furnace. You may want to look at the sticky at https://www.askmehelpdesk.com/heating-air-conditioning/heating-cooling-maintenance-repair-troubleshooting-frequently-asked-questions-58313.html