Nest thermostat issue

[Mikemoke]

Hello, I have an issue when installing my nest. First I encountered the unconfigured/undetected C wire. but also the thermostat is starting the condenser unit and sending cool air when heat is selected. I’m attaching picture of my old thermostat.

[Houptee]

Do you have a Heat Pump system or a gas furnace with AC?

[Mikemoke]

No heat pump. Just AC and heat

[Houptee]

Can you go check the furnace and see if the blue wire is actually connected to the C screw on the furnace.

Trane brand calls common B so see if it is hooked to C or B or post a pic of the screw terminals in the furnace.

[CoolingWizard]

Your old thermostat is for a conventional HVAC system. And your wires are connected properly. As long as you did not change the Nest Thermostat wire functions, all should be working as it did in the old thermostat. Please describe for us how you set up the thermostat when you installed it using the Nest App? Go into settings and choose equipment. Your system should be set up as dual fuel, Air Conditioning with Forced Air, and Gas Furnace with Forced Air.

Ken, The AC Cooling Wizard

[Mikemoke]

Good evening, I still have the undetected/unconfiguered wire issue

[Mikemoke]

It even says empty in the app

[CoolingWizard]

In some of the older systems, they did not have a Common terminal labeled C. They used B terminal for the termination of the Power Common. Some technicians pre wire the common wire and many do not. It is possible the common wire is not attached in the air handler.

Ken, The AC Cooling Wizard

[Mikemoke]

Would that explain that it does not start the heater but the condenser and/or the furnace

[Houptee]

read this info

https://support.google.com/googlenest/answer/9244860?hl=en

[Mikemoke]

[Mikemoke]

There is something weird…I never configured the system like this and it always end up with these settings that I cannot change…additionally, my secondary unit upstairs which is exactly the same doesn’t have the same wirings, see screenshot please.

[CoolingWizard]

This latest photo shows that that thermostat is controlling a heat pump and the first thermostat you show the picture of was not a heat pump wiring system.

[Mikemoke]

first picture is from my 1st story unit, the second one is for the 2nd story unit. I went to the attic and took pictures of the units control panel

[EdwardT]

Hi folks,

@Houptee and CoolingWizard, thanks for the help as always!

@Mikemoke, how's it going with your Nest Thermostat? Still need our help?

Thanks,

Edward

[EdwardT]

Hi Mikemoke,

It's me again. I wanted to check back in to see if you have other questions and concerns. Feel free to let me know if you do. 

Thanks,

Edward

[EdwardT]

Hi Mikemoke,

I'm just checking in to make sure that you've seen our response. Please let us know if you have any other questions or concerns as I will be locking this in 24 hours.

Thanks,

Edward

[Mikemoke]

[Mikemoke]

I don’t have a heat pump

[CoolingWizard]

Those control boards are manufactured by White Rogers and is found often in Trane Gas Furnaces.  It is designed to support up to 2-stages of heat. Here you see that the installer put a jumper between W1 and W2.  The Common is labeled B/C.  If you note this board it is designed to support type O heat pumps. Also note that there is a Blue wire jumped between O and Y1 and there is no O wire seen here and going to the outdoor unit.  Heat pumps generally have 3 wires used between the indoor  and outdoor units.  They are R, C, and Y2. When a Heat Pump goes into the defrost cycle, it signals this using the Y2 or YLO.  This outdoor unit is not a heat pump system. You can note a red wire on R and a white wire on B/C and this is likely part of the thermostat cable going to the outdoor unit.  The Yellow, Green, and Blue wires are folded back on the outer cover in the unit marked “UP” in yellow.  Now let’s talk about the two stages of heat.

The furnace has a two stage gas valve. When the Thermostat energizes W1 and the control board starts the heat cycle. If the temperature continues to drop, the thermostat will add W2 and the control board will open gas valve stage 2 which increases the gas flow. When the thermostat detects the temperature rise, it will de-energize W2 which change the gas valve back to stage 1. When you change your thermostat to a set point 3 degrees higher than the current room ambient temperature, this will also case a W1 and W2 call. On the UP/1ST unit, they wired it with W1 and W2 jumper together.  This makes this unit be at maximum heat anytime heat is called for by the thermostat.  This usually required when the thermostat does not support 2-stage heating. 

The UP unit has Common on a Black Wire and the 1st/DOWN unit has it on a blue wire.  

Your thermostat is not configured properly since it has been set up as a Heat Pump and that why your outdoor compressor it being turned on when in heat mode.  

Ken, The AC Cooling Wizard

[Mikemoke]

Thank you for this analysis. My condensers are xli15 trane and yes the furnaces are 2 stages furnaces. But I haven’t set ut the thermostat as a a heat pump. I even answered NO at this question during set up…I stripped the blue wire and it is still undetected\ unconfigured

Do you also mean that the 2 stage furnace downstairs wasn’t installed correctly?

[Houptee]

Go outside look at the Model # on the units

If it starts with 4TWX  it is a Heat Pump

4TTX it is a standard AC only

[CoolingWizard]

OK, I have resisted to this point but you now have provoked me enough. If you look closely at the picture you see that the picture submitted by Mike. Can you see the cable going to the outdoor unit. I saw it instantly.  I have edited the photo to help you see. There is only a red wire and a white wire being used to connect to the outdoor unit. One of those obviously is the common. It is connected to the B/C screw and the other one is the red wire connected to the Y. There is not a third conductor being used for a reversing valve.  It therefor is not a heat pump.  

[Houptee]

Looked like it said B/O and his Nest configuration pics all show he set it up as a Heat Pump so I thought he did not know what kind of system he actually has.

The way to settle the issue is post the model number of the outside unit so everyone knows what we are trying to make run!

Just trying to help people on here for free as a volunteer.

As you know this website most people have no idea what kind of system they have in their home. 

[Houptee]

Looks like both have a B/O screw that usually is a heat pump.

Look up the model number decal of the indoor and outdoor units on the internet see if it says Heat Pump system.

[CoolingWizard]

Here is the White Rogers (now American Standard) installation instructions. Listed at the bottom is the B and O, note that O and YLO are not interfaced with the control board. They are simply landing points.  

Ken, The AC Cooling Wizard

[Houptee]

Strange that the installer put jumpers on Y to O. Wonder what his thinking was if this is not even a heat pump. 

Also he defeated the 2 stage heat feature by jumping w1 and w2.

And he wired 2nd floor thermostat as a heat pump.