Using indoor furnace fan with outside ac using nest thermostat


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Old 06-06-24, 04:56 PM
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Using indoor furnace fan with outside ac using nest thermostat

Hello everyone, my name is Josh and I am a manufactured home owner. I recently installed a new AC and everything is working properly as long as I wire the units separately come winter or summer. I have made a couple attempts at wiring them together but they have failed. Well now I am trying g to at least use my furnaces fan with my ac system even if I have to bypass the fan switch. Problem is there's no fan wire so the fan switch seems to be triggered by the system.
If anyone can help me figure out how to get closer to a solution to my problem I would be able to cool my home down a little better as it is getting hotter every day I would greatly appreciate support.

This is the indoor coleman direct vent forced air furnace


Smaller wire are to the A/C, the 3 thicker wires are for the furnace


This is the Outside A/C unit.
 

Last edited by PJmax; 06-06-24 at 05:09 PM. Reason: resized/labeled pics
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Old 06-06-24, 05:12 PM
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Welcome to the forums.

Very do-able.
You will need a 24vac SPST or SPDT relay. About $15.
It will install in the furnace near the transformer.

Where are you getting the Rc power ?
I need two more pictures.... the circled areas.
That's the transformer wiring area and the wiring diagram.
 
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Old 06-06-24, 11:36 PM
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Thank you for reaching out, im glad this is possible and thank you for help.
Rc power is coming from A/C in the first Pic with the thermostat wire I believe is how I hooked it up when i installed the ac.


Let me know how the quality is on the pictures i can help if it isnt readable
 
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Old 06-07-24, 09:02 AM
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Old 06-07-24, 03:00 PM
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This is the furnace inside, does the common wire have to go to the AC condenser outside? They are separate systems.
also just so you can confirm for me the current wiring has bypassed the fan switch correct? I'm just making sure that what I am seeing is correct so far.
 
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Old 06-07-24, 03:48 PM
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Rc power is coming from A/C in the first Pic
The first pic is the Coleman furnace.

If the furnace doesn't move the cold air..... what does ?
Do you have a separate A/C air handler ?
If you have two separate air movers.... do they share the same ductwork ?

Is that outside A/C unit a packaged unit...... everything in one ?
 
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Old 06-07-24, 03:50 PM
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Yes they share the same ductwork correct.
yes the outside unit is a packaged unit.

so I would like to use my furnaces blower with my package AC unit to deliver a stronger force of air during the summer months
 

Last edited by Dabneyskeys; 06-07-24 at 04:24 PM.
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Old 06-07-24, 05:17 PM
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Ok... that's different.

Original diagram nixed.
You will still need a 24vac relay.
It will still connect to Y and C at packaged unit.

 
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Old 06-07-24, 05:53 PM
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And this will make my furnaces blower turn on with my packaged ac unit and back off when the packaged ac unit turns off.
Now when winter comes will the furnace still work normal?
also can this cause any damage to my furnace?

Thank you for everything I have the parts and will keep you updated on my success.
the relay i got my hands on has prongs in an L shape instead of H but I think I can figure it out.
 
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Old 06-07-24, 08:08 PM
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Post the relay part number.
The relay will not effect heat operation in the winter.
Running the blower via the relay will not cause any damage.

I can't comment on how both blowers on together will work.
That you will need to assess.
 
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Old 06-08-24, 09:32 AM
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Relay is a white Rodgers 90-290Q Type 84
Also quick question do the C and the Y1 wires coming from the AC to the Relay have to be a minimum Guage? Or can I use the existing thermostat fan wire since I don't use the packaged units fan by itself?
now that I think about it I feel that I need to run thicker wire
 

Last edited by Dabneyskeys; 06-08-24 at 09:56 AM.
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Old 06-08-24, 12:33 PM
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Amy wire can be used to run the relay. The draw is minuscule.
 
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Old 06-08-24, 03:04 PM
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Okay that's good news. One more question. Are you familiar with a way I can wire both furnace and Outside packaged ac unit to the same nest thermostat once and for all as well as the furnace fan operating in conjunction with the outside unit of course?
 
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Old 06-09-24, 03:22 PM
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Unfortunately I realized this cant function properly if I don't have the furnace and packaged unit hooked up at the same time thermostat at the same time
 
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Old 06-10-24, 02:25 PM
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Originally I told you to connect the relay to Y and C. Since you have a G to the thermostat the relay can connect to C and G instead

The wiring currently on the nest should provide for year round service.
I would like to see a C connection to the packaged unit.

You only have three wires between the nest and the packaged unit.
You could make wiring changes so that.....
Y1 = white = Y & G & relay.
Rc = red = R
C = green = C

With this wiring..... when the nest commands cooling.... the Y1 becomes live powering the compressor, the blower and the relay for the furnace blower. You will not have separate blower control at the thermostat.
 
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Old 06-10-24, 03:40 PM
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This is my rough idea how does it look?
also this would mean the green wire becomes the C now I just have to take the panel of the packaged unit and take the green wire off fan and locate and attach it to C
 
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Old 06-10-24, 03:47 PM
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The relay is powered only from the packaged unit.
You've removed all those connections.

IF there is any wire in Y1 or Y2 on the nest... then C MUST come from the A/C unit.
 
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Old 06-11-24, 08:39 AM
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Ok that was my other question. Don't lose me yet. I think I got confused from your previous diagram before you understood it was a separate unit.
 
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Old 06-11-24, 03:39 PM
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Here's a simplified diagram......
 
 

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