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Old 07-27-2020, 08:44 PM   #1
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No "Y" wire to furnace???


Just bought a new house couple weeks back, went to go throw on my Honeywell smart thermostat and boom no "C" wire on the old thermostat. No big deal, blue wire dangling inside the wall so I knew what to do.

Got down to the furnace and pulled off the cover and everything is wired odd. Green, white and red were wired as expected to the thermostat. Yellow had no wire and Common is going to the condensor returned back and is linked to yellow which runs to the thermostat but not back to the furnace.

So I ended up adding the blue wire common from the thermostat back to the furnace, and my smart thermostat powered up fine and responds fine.

My question (sorry for so much intro) is we are getting really poor air flow on the 2nd floor of the house. We already had a service tech out who added refrigerant to the system and it cools better, but the 1st to 2nd floor temperature difference can be 5 - 7 degrees F at times. What I'm wondering is the way this is wired the furnace is not getting notified of cool on because the yellow terminal is empty? Yes the blower does respond to cool on, but that fan speed is probably a response to auto fan not cool fan.

I'm wondering if I rewrite it so yellow runs directly to furnace if that would give me more blower speed and improve air flow upstairs and reduce temperature gradients?
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Old 07-27-2020, 08:50 PM   #2
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Re: No "Y" wire to furnace???


Whatís the model number of the air handler? Do you have an ECM blower?
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Old 07-27-2020, 08:53 PM   #3
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Re: No "Y" wire to furnace???


amana 90 air command

How would I know about a ECM blower???
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Old 07-27-2020, 08:55 PM   #4
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Re: No "Y" wire to furnace???


Get the complete model number off the rating plate.
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I am not in the business of any trade I give advice on. I have non-professional hvac experience + good knowledge of theory. Attempt repairs at your own risk. Never jump out safeties - especially pressure switches - on a furnace for testing with fuel supply on; use a meter. Do not troubleshoot with live line voltage present unless there's no alternative.
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Old 07-27-2020, 09:01 PM   #5
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Re: No "Y" wire to furnace???


Lookup the full model number, itíll say it
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Old 07-27-2020, 09:03 PM   #6
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Re: No "Y" wire to furnace???


Not seeing one unit is 15+ years old. Did find a number in side that matched this https://manualzz.com/doc/1137270/ama...al-information
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Old 07-27-2020, 09:12 PM   #7
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Re: No "Y" wire to furnace???


guca090AX50 found it inside the furnace area
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Old 07-27-2020, 09:18 PM   #8
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Re: No "Y" wire to furnace???


Y terminal on older furnaces is just a dummy terminal to splice between the thermostat and outside unit. G turns the fan on and off controlled by the thermostat. Y turns the condenser on and off.

When I wired my A/C years ago, I had a 2 wire running to my thermostat for R & W. I left that alone and ran another 2 wire to the thermostat for G & C. I ran a 2 wire from the thermostat to the outside unit for Y & C. No Y back to the furnace. All functions correctly and my house is 69 degrees right now
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Old 07-27-2020, 09:20 PM   #9
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Re: No "Y" wire to furnace???


I'd agree with you expect that i am getting zero flow on 2nd floor. If I do have a ECM or variable speed blower the furnace blower settings are not optimized for AC so that may be a reason I get poor flow upstairs. A coil temperature is good after a refrigerant refill, but can't get that nice cold air up to the bedrooms

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Y terminal on older furnaces is just a dummy terminal to splice between the thermostat and outside unit. G turns the fan on and off controlled by the thermostat. Y turns the condenser on and off.

When I wired my A/C years ago, I had a 2 wire running to my thermostat for R & W. I left that alone and ran another 2 wire to the thermostat for G & C. I ran a 2 wire from the thermostat to the outside unit for Y & C. No Y back to the furnace. All functions correctly and my house is 69 degrees right now
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Old 07-27-2020, 09:22 PM   #10
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Re: No "Y" wire to furnace???


Fan only mode on this furnace uses the cooling speed so it shouldn't make a difference - https://www.manualslib.com/manual/79...page=38#manual
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Old 07-27-2020, 09:26 PM   #11
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Re: No "Y" wire to furnace???


Except I'm running it on cool with fan to auto so my fan setting is likely in heat mode given the wiring on it?


I am going to try something now to see if this works. Have it on cool on + auto fan check speed up stairs then kick it off and go to fan on.

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Fan only mode on this furnace uses the cooling speed so it shouldn't make a difference - https://www.manualslib.com/manual/79...page=38#manual
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Old 07-27-2020, 09:28 PM   #12
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Re: No "Y" wire to furnace???


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Originally Posted by cooldude832 View Post
I'd agree with you expect that i am getting zero flow on 2nd floor. If I do have a ECM or variable speed blower the furnace blower settings are not optimized for AC so that may be a reason I get poor flow upstairs. A coil temperature is good after a refrigerant refill, but can't get that nice cold air up to the bedrooms
I am an electrician, not an HVAC guy, but I would try partially closing of the supply vents on the 1st floor. This will force more air upstairs assuming this is a single zone system. If you have return registers in both floors and they have filters behind the grill, make sure they are clean. Put an expensive (more restrictive) one in on the 1st floor and a cheapo fiberglass one in on the 2nd.
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Old 07-27-2020, 09:31 PM   #13
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Re: No "Y" wire to furnace???


Quote:
Originally Posted by cooldude832 View Post
Except I'm running it on cool with fan to auto so my fan setting is likely in heat mode given the wiring on it?


I am going to try something now to see if this works. Have it on cool on + auto fan check speed up stairs then kick it off and go to fan on.
The t-stat applies power to G/fan terminal with a call for cooling.

You probably have lousy ductwork. Could also be a dirty blower wheel, secondary heat exchanger and or evap coil.
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Old 07-27-2020, 09:33 PM   #14
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Re: No "Y" wire to furnace???


That's my next step is to try and restrict the 1st floor return so we suck a bit more of the warm upstairs air down and get flow.

I did just swap from auto fan to on mode and there is more flow so I'm confident the wiring is wrong. My issue is I have a home warranty and the tech came last week and didn't notice this issue. If I move it now and screw something else I may cost myself my warranty. I guess I'll either try and program some more fan on settings on my smart thermostat and get circulation until I can get a follow up tech out on my system in a week.

Quote:
Originally Posted by JoeSparky View Post
I am an electrician, not an HVAC guy, but I would try partially closing of the supply vents on the 1st floor. This will force more air upstairs assuming this is a single zone system. If you have return registers in both floors and they have filters behind the grill, make sure they are clean. Put an expensive (more restrictive) one in on the 1st floor and a cheapo fiberglass one in on the 2nd.
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Old 07-27-2020, 09:45 PM   #15
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Re: No "Y" wire to furnace???


Be careful closing vents to get more flow on the second floor, older blower motors don't compensate for increased duct pressure so you can end up freezing the indoor coil.

setting the fan to on didn't make a difference beyond placebo, otherwise the fan wouldn't have come on at all without Y connected to the board.
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