Is this nest wired incorrectly?

[mayorblurps]

System is 6 mos old - furnace, coils, compressor. Gas heat. Technician installed the nest when ecobee died last week and heat wasn't working. Seemed to fix issue only it didn't. 2nd technician came back and said Nest signal is dropping off before it gets to control board, thus no heat to target temp - said it had to be the thermostat. Bought a 2nd Nest, installed it. Tests ran fine. Today, same issue - heat will not turn on.

My concern is that with all the nests I've used, the red wire is usually used? Should brown wire be in O/B?

Unfortunately I did not see where wires were before ecobee was removed AND I don't know if that was wiring for the previous HVAC system. Please advise

 

[mayorblurps]

There's an unused red wire hiding behind the brown one. Hard to see in pic.

[CoolingWizard · Accepted solution]

You stated you had Gas Furnace for heat.  You would only need the O/B wire if your Outdoor Unit is a Heat Pump. It is unlikely you have both a heat pump and a Gas Furnace, but it does happen.  These are called Dual Fuel systems.  To test this you need to have a technician test the AC voltage between Rh and C.  Then turn the heating system on and measure the current on the W1 wire voltage arriving at the air handler/furnace. 

AC Cooling Wizard

[mayorblurps]

Hey wizard, thanks for the reply. I was going crazy trying to understand why the Nest wasn't forcing the furnace on (and furnace was working sporadically irregardless of the t'stat). I knew things were wired correctly and everything should be working + brand new furnace and handler.

Had HVAC come back out. As it turns out, 1. the old red wire is from the old furnace/air handler system and moot point. 2. The Rheem furnace is brand new but does not have a read out screen or indicator lights on the unit itself. Touching the wires together proved the furnace was working, but would kick off unexpectedly. Positively, it is a unit with Bluetooth that I can monitor via app, as can the HVAC company. And 3. The issue was NOT the nest but a sensitive water sensor that kept triggering each time the furnace kicked on when Nest sent signal to turn on the heat. Technician could see a ton of water sensor errors from the last week in the Rheem app.

So, since repair, the Nest has worked beautifully without issue. And the brown wire is my "red" wire on the new system. 

Thank you for the feedback all the same. Issue resolved. 

[CoolingWizard]

@mayorblurps , the furnace does not have a water sensor or should not have a water sensor on it. The air conditioning coil does. And here’s the key. The furnace has a very specific start cycle. First, there is less known as an induction fan motor. This is a small motor that turns on to create a vacuum inside your fire chamber. This proves that there’s no leaks in the fire chamber, and therefore no chance of getting carbon monoxide into the airstream. Once the vacuum is confirmed by the vacuum sensor, the control board receives that and then starts the igniter. Once the igniter gets hot enough to ignite gas, then it sends a signal to turn on the gas valve. The gas starts flowing, and it should ignite, and then the flame sensor within 6 ms should sense the flame and if it does, the gas valve will stay on. But if it does not see a flame immediately turns to gas off and starts the induction fan motor for five minutes to evacuate any unburned gas.   

If your furnace is lighting and then turning off, that sounds like you either have a bad flame sensor or possibly you have a problem with your vacuum sensor. Either way if it’s six months old and still covered by the manufactures warranty.  Your HVAC company should do a thorough product test of the Ferner system and verify all the tolerances on all the sensors to make sure that they’re working properly.  

The AC Cooling Wizard

[mayorblurps]

It is my understanding, based on what you just explained, that the HVAC technician found the issue with the water sensor as you described it. We had the entire system replaced (furnace, AC, coil) in July. No issues until we started trying to use heat. The technician was under the house for a good while going through the system checks - I live in a state where unfortunately they still install the HVAC systems under the house. It was their 3rd trip out, thankfully this time it was resolved since the first 2 visits the other 2 technicians believed it was a malfunctioning ecobee and then a brand new Nest. Repaired under warranty!

I tried to attach a screenshot of the neat Rheem info but replies don't allow it.

[CoolingWizard]

@mayorblurps , the gas furnace does not produce water. The air conditioning coil does. And here’s the key. if there is water standing in the base pan, then there is a drainage problem. It can be caused by incorrect installation or improperly plumbing of the drain line.  
The furnace has a very specific start cycle. First, there is less known about induction fan motor. This is a small motor that turns on to create a vacuum inside your fire chamber. This proves that there are no leaks in the fire chamber, and therefore no chance of getting carbon monoxide into the airstream. Once the vacuum is confirmed by the vacuum sensor, the control board receives the signal and then starts the igniter. Once the igniter gets hot enough to ignite gas, then it sends a signal to turn on the gas valve. The gas starts flowing, and it should ignite, and then the flame sensor within 200ms should sense the flame and if it does, the gas valve will stay on. But if it does not see a flame immediately turns to gas off and starts the induction fan motor for five minutes to evacuate any unburned gas. When we install a safety float switch, we interrupt Y wire and not the R wire.  

The AC Cooling Wizard