If you can not go to Zone 2 - (Zone change is done by pressing the top 2 buttons and releasing at the same time) If Zone 1 does not display (small “1”) and the Zone 2 DIP switch is ON, there is a fault with the communication cable (Phone cable) from Zone 1 to Zone 2 and the thermostat cannot detect Zone 2 which is necessary to show the zones on the display. Un-plug and re-plug the RJ-11 connectors to wipe the contacts. If no change, run a test cable from Z-1 to Z-2 with the thermostat connected to Z-1. If no change with test cable there is a fault with Z-2 control board. The communication cable is different (parallel wired) that a phone extension cable (series wired).

If the Air Condition will not come on -- First select a fan speed and if the fan does not come on in about 6 seconds the possibilities are : a dead spot or a bad fan motor (rotate the fan blade and try again) - be sure 120 V is available on the Black wire in the junction box. --IF 120 volts available reset the breakers. If 120 V is available probably a faulty control board. After getting the fan to function, select COOL and set a low temp. The compressor should start in 2 to 3 minutes -- If not – possible bad compressor or faulty control board.

If Furnace will not display -- The Control Board must receive 12 volts from the furnace on either one of the 2 blue wires at the control board. Check the furnace fuse, if OK possible break in the line or bad furnace board. Shorting across the two blue wires should make the furnace come on if voltage is present on one of the 2 blue wires and IF the furnace control board is OK.

If you have a Heat Pump and it gives heat when the controls are set for Cool, this is usually a stuck reversing valve of the Freon system. First verify that the reversing valve electrical coil is getting 120 volts from the control board -- if no 120 v, bad control board. If yes 120v, tap on the reversing valve while the compressor is running to see if it will activate and start to cool. If the valve is permanently stuck compare cost of repair to cost of a new air condition. Run the air condition each month to keep the reversing valve lubricated.

NOTE: Mice love to eat your RJ11 cable usually starts with the outer 2 wires which provides comunication between the thermostat and AC control panel. This sometimes Allows the 12-Volt testing OK at thermostat... EASY TEST -reroute a new phone cable direct from thermostat and control panel with separate RJ11 cable or move thrermostat to the A/C control panel to connect direct, bye passing the OEM wall wire.