Troubleshooting Furnace No Longer Activating After Installing Advent 15K AC and Thermostat ACTH12

Updated 05/15/2025 | Published 11/20/2023

Question:

I installed the new Advent 15000 ac unit with the ACTH12 thermostat to replace a domestic unit, now the furnace wont come on, any suggestions?

asked by: Bruce S

Expert Reply:

The Digital Thermostat ACTH12 is a confusing thermostat since it can be used with heat pumps, heat strips and furnaces. First you will want to make sure you have the dip switches on the back of the controller set up correctly. If you are just using the Advent # ACM150 for cooling and the furnace for heat you will need to have switch 1 and 2 set to off. the number 3 switch needs to be in the on position. Switch 1 is for a heat strip while 2 is for a heat pump. Next you will want to verify the wires on both the thermostat and air conditioner are wired correctly for their function.

If all this is correct be sure to verify if the signal is getting to the furnace as you could have an issue of a short in the travel wire. If your furnace is getting a signal you will want to check and clean the furnace. Please let me know what all tests and steps you have performed and if you are still having trouble after checking these areas. Then I can best judge how to proceed with troubleshooting your furnace issue.

expert reply by: Bud M

Kent

5/10/2025

If I change the dip switches will I be able to cycle from furnace to heat strip?

Nick S.

5/15/2025

@Kent Hey Kent you can absolutely do that. I spoke with Advent and if you are wanting to do that you will need to have the switch 1 in the on position, the switch 2 in the off position, and the switch 3 in the on position to cycle the heat strip and furnace.