Combining two units on 1 thermostat


  #1  
Old 06-20-22, 12:37 PM
D
Member
Thread Starter
Join Date: Jun 2022
Posts: 2
Received 0 Votes on 0 Posts
Combining two units on 1 thermostat

Redoing a house that had a Trane/american standard air handler in the attic for AC (schematic attached) and a new boiler in the basement for hydronic baseboard heat. I pulled the second 2-wire thermostat for the AC out and ran a new 7 wire to the air handler but I realized i need an assist once i pulled the panel.

I know i need a common because the thermostat is on battery (boiler is not powering it... figured i would get it from air handler) and I'm pretty sure that's the Blue. Red to RC(?). But other than that Im unsure.

There is a red/white going out the the condenser. And the thermostat has the 2 wires from the boiler connected (red & white).






 
  #2  
Old 06-20-22, 09:11 PM
A
Member
Join Date: Jun 2012
Location: USA
Posts: 1,792
Received 81 Votes on 73 Posts
I don't see any pics of wires coming from the boiler.

It doesn't make sense for the white wire at the air handler to connect to the white in your picture. Assume the red and white in the brown thermostat cable goes to the outside unit. So one of those two wires needs to connect to the thermostat Y and the other the air handler's C.

Basic setup would be like this: https://f01.justanswer.com/wWRjbmoT/Capture.JPG
 
Danny K voted this post useful.
  #3  
Old 06-20-22, 10:52 PM
D
Member
Thread Starter
Join Date: Jun 2022
Posts: 2
Received 0 Votes on 0 Posts
At the thermostat (pic 2) there is the white (W) and red (RH) - those are from the boiler.

So from your diagram (which is really helpful btw), for the red and white there at the air handler (which go outside) - the red is C and the white is on the WH/1...which I'm assuming in this case would be my yellow? So for my new wire:
I tie Green to Green (Fan)
Yellow to the WH/1 (the two whites already there)
Blue to Blue (C) (combining with the existing blue and red)
and Red to Red (Rc)



 
  #4  
Old 06-21-22, 05:57 AM
A
Member
Join Date: Jun 2012
Location: USA
Posts: 1,792
Received 81 Votes on 73 Posts
Sorry - my eyes didn't see the boiler white and red until I zoomed in.

Yes, the connections you mentioned should work.

The white from the outside and the yellow from the thermostat should be connected to each other but not to WH/1. WH/1 is to activate any option electric heating coil in the air handler. If the heater coil is not installed things will work, just confuse the next tech.
 
Danny K voted this post useful.
 

Thread Tools
Search this Thread
 
Ask a Question
Question Title:
Description:
Your question will be posted in: