After Nest thermostat A/C doesn't seem to cool properly

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Old 07-13-19, 07:16 PM
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Question After Nest thermostat A/C doesn't seem to cool properly

ello,

I yesterday I install my new Nest thermostat (3rd gen) and the Nest App guide wasn't sure how to wire up my system so it told me to call customer service. While on the phone they asked for my original wiring and then sent me a new wiring how to wire up the Nest.

All seemed to be working fine but later I noticed that the system doesn't really "cool" like before. I'm in Florida and today I was lucky that it was cloudy and not too sunny. Even so the house temp stayed between 80 and 83 the whole day no matter how low I set it (I had it down to 70 for over 3-4 hours as a test) and didn't make a difference.

Both inside unit and outside unit are working and the nest can control them yet they don't cool properly. I have an infrared thermometer and when I point it at the A/C vent it reads between 79F and 81F so it's not properly cooling at all. Only one time today it was actually working for a little bit and it was reading low temps in the high 60's but that was short lived.

I'm attaching my original wiring and the one they had me do for the nest in hope of somebody telling me if the wires are OK. I was using 6 wires before but they told me to just wire 4 to the nest leaving out white and blue.

Note when looking at the original wiring, the white wire was in the BK spot which I'm guessing was a mistake since W1 was next to it and it was empty.

At this point I'm afraid we have left some wires out that would otherwise be needed. I know Yellow is the important one for the A/C compressor but still. Also there was a Brow and Black wires tucked in the wall not used at all so that's there for an FYI, not sure if needed.

Old thermostat: Trane Nexia XL824
New thermostat: Nest 3rd gen

From the Nest app it also says:

Heat source: Electric
Heat type: Forced air
Heat pump orientation: O

Both the inside and outside units are from Lennox but I don't have exact model numbers. Let me know if those are needed.

Thank you for any help!

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Last edited by PJmax; 07-14-19 at 12:43 PM. Reason: reoriented/resized pictures
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Old 07-14-19, 06:54 AM
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Hi, is your system a Heat Pump?
Geo
 
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Old 07-14-19, 12:37 PM
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Welcome to the forums.

Why are you replacing a good wifi thermostat with a nest ??

You may need to make a wiring change at the air handler. The BK wire is used for blower speed control and dehumidification. Are you 100% sure the white wire wasn't on W1 ? Currently your stat does not show electric back up heating for your heat pump system.

BK -------> white -------> ??
G ---------> green ------> G
Y1 -------> yellow ------> Y1
O --------> orange ------> O/B
B/C ------> blue ---------> C
Rh/Rc ---> red ----------> Rh

the white wire was in the BK spot which I'm guessing was a mistake since W1 was next to it and it was empty.
I placed an arrow in your picture. You can confirm thermostat wiring there. See where the white wire is connected.
 
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Old 07-15-19, 09:56 PM
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Hi there! Thanks for the reply and help. The white wire was definitely in the BK spot. Your can even see in the photo next to the wire the BK label is embossed in the plastic. I even counted the spots from last to right and it's the BK one.

Anyway, that same night I decided to try the Nest rep's "plan B" and connect the blue wire to C and that fixed it. Now the A/C is working properly. I'm guessing the solenoid that moves the valve body of the reversing valve wasn't working correctly without the blue wire so it was just pumping the hot freon without cooling it

I don't know if I'm making sense since I'm no HVAC pro but just wanted to say that the system is working now after the addition of the blue wire.

Thanks again for the help!
 
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Old 07-15-19, 10:07 PM
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Yes.... the system is cooling but what about heat ?
Since your wiring doesn't show it..... you do not have backup electric heat...... correct ?
 
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Old 07-17-19, 06:03 AM
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Hi, does that stat require programming for a heat pump?
Geo
 
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Old 07-23-19, 06:58 PM
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Yes.... the system is cooling but what about heat ?
Since your wiring doesn't show it..... you do not have backup electric heat...... correct ?
I'll have to test heating at night because during the day it says it won't turn on the heater if it's above 85F outside in order to protect the system. As far as backup heat I think you're correct I didn't see any mention of a backup/aux/emergency heat so I'm assuming I don't have it.

Hi, does that stat require programming for a heat pump?
Geo
Hi Geo, not sure what you mean but other than the wiring I did have to go through the Nest setup and tell it what kind of a system it was before it was able to start.

P.S. Please let the admins of these forums know that the emails we get for notifications of a new post contain staging links to the forum so they don't work. They look like:

https://stg-diy.internetbrands.com/f...d.php?t=607915

Thanks guys!
 
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