topic Re: 2nd Gen Nest not activating 2nd Stage Cooling in Nest Thermostats

2nd Gen Nest not activating 2nd Stage Cooling

RE4 — Thu, 03 Aug 2023 21:36:50 GMT

I have an American Standard Heritage 18, Model-2A6H8060A1000AB, dual compressor heat pump with natural gas supplemental heat, mfd’ in 03/2005. I have installed a new 2nd Generation Nest Learning thermostat. It seems to work fine, except the Nest is not activating 2nd stage cooling when I believe it should. I had one professional HVAC guy check my wiring, and another who said the thermostat might be broken. The last guy uninstalled the Nest and reinstalled the original American Standard thermostat, and the 2nd stage cooling was activated. I don’t know if the Nest was wired incorrectly, or if the 2nd stage cooling circuit on the Nest is broken.

I’ll try to post some photos of the wiring flow from the outside unit to, a terminal strip in a box on the outside of the indoor unit to, a terminal strip inside the indoor unit to, the wiring of the original and the Nest thermostats.

Any help would be greatly appreciated!

Rick

Re: 2nd Gen Nest not activating 2nd Stage Cooling

RE4 — Thu, 03 Aug 2023 21:42:19 GMT

I hope these photos help.

Re: 2nd Gen Nest not activating 2nd Stage Cooling

RE4 — Thu, 03 Aug 2023 22:07:52 GMT

Additionally, I have these other questions to complete my understanding of how these things are wired:

1. Since my heat pump has two compressors, and natural gas supplemental heat, in HVAC parlance does that mean it has two stage cooling, and three stage heat?

2. Does the wiring code of ?3, i.e. X3, Y3, W3, on a terminal strip indicate that is the wire that goes to the thermostat. Like does Y1 and Y2, roll to Y3 and then Y3 goes to the thermostat as Y, or Y1?

3. Is W1-1st stage heat, W2-2nd stage heat, and X2-gas heat?

4. Does X2 and W2 roll to W3 and go to the thermostat as W2/AUX?

5. The old American Standard thermostat had two terminals labeled OT. There was a separate 3 conductor wire group that had green-red-white insulated wires in it, the red and white wires went to these two OT terminals. Were they perhaps for sensing outside air temperature?Do/should they play any role in the proper wiring of the Nest?

6. The Nest has two terminals I did not use. They are labeled ALT STAGE 2, and RH. Do/should they play any role in the proper wiring of the Nest?

Thanks to anyone who can help me with this knowledge!

Rick

Re: 2nd Gen Nest not activating 2nd Stage Cooling

CoolingWizard — Fri, 04 Aug 2023 02:49:59 GMT

@RE4 ,

1. Since my heat pump has two compressors, and natural gas supplemental heat, in HVAC parlance does that mean it has two stage cooling, and three stage heat?

Your heat pump is a 5-ton R22 based heat pump with two 2.4 ton compressors. Your outdoor unit requires a special wire harness adapter for using a conventional thermostat. Each compressor has dual stages. The control board in the outdoor unit is want accepts the second stage cooling call.

2. Does the wiring code off ?3, i.e. X3, Y3, W3, on a terminal strip indicate that is the wire that goes to the thermostat. Like does Y1 and Y2, roll to Y3 and then Y3 goes to the thermostat as Y, or Y1?

You do not have 3 stages, but there are systems with 3-stages. You have a Duel-Fuel system. The Electric is the heat pump and the second is your gas furnace. I notice your dual stage gas furnace has W1 and W2 (stage 1 and stage 2) are connected to each other with a wire jumper. The control box on the outside looks like an electric heat stager but you say you have gas heat.

3. Is W1-1st stage heat, W2-2nd stage heat, and X2-gas heat?

In the heat furnace world with gas heat, W1 is stage 1 heat, and W2 is stage two heat. The X2 is heat pump emergency heat. The Nest presumes that on a duel fuel heat pump system, the primary heat is electric heat pump. The secondary heat is presumed to be electric heat strips in the air handler. These heat strips are the auxiliary heat (W2) and the emergency heat (X2) With a dual fuel system, the W1 is stage 1 alternative heat and * is stage 2 secondary heat.

4. Does X2 and W2 roll to W3 and go to the thermostat as W2/AUX?

X2 and W2 are only used in single fuel heat pump applications. These are Auxiliary Heat (W2) and Emergency Heat (X2) both are same electric heat strips in the air handler. W2 is 100% controlled by the heat pump defrost board and the thermostat. The thermostat would activate auxiliary heat when it determines the heat pump is not keeping up. Ie., the ambient temperature indoors continues to drop. It that situation the thermostat will activate W2. The purpose of Emergency Heat is so a homeowner can activate the more expensive heat strips in the case the heat pump is out of service. This way you have heat in the home while wit for the repairman to arrive.

The Outdoor Temperature sensor is not needed by the Nest Thermostat. Nest uses the WiFi and get the weather from the internet.

6. The Nest has two terminals I did not use. They are labeled ALT STAGE 2, and RH. Do/should they play any role in the proper wiring of the Nest?

The RH is for power in from a separate heating system. Your heating system is combined with your heat pump air handler. Even though you have a gas furnace, it uses the same forced air system. The power for then control system comes from this air handler.

There are three separate cables thermostat cables entering the controller on the outside of the cabinet. One goes to the thermostat, one goes to the furnace control board. Where the third go or come from? This controller appears to be some kind of sequencer for stage 1 and stage 2 heating and cooling.

AC Cooling Wizard

Re: 2nd Gen Nest not activating 2nd Stage Cooling

RE4 — Fri, 04 Aug 2023 06:03:08 GMT

@CoolingWizard , thank you so much for your detailed explanation to my questions.

Did you see anything in the wiring of the Nest that was incorrect, to the point that the 2nd stage cooling would not be activated?

Rick

Re: 2nd Gen Nest not activating 2nd Stage Cooling

CoolingWizard — Fri, 04 Aug 2023 14:58:05 GMT

@RE4 ,

can you describe for me what action you took on the nest thermostat in an effort to try to activate stage 2 cooling?

AC Cooling Wizard

Re: 2nd Gen Nest not activating 2nd Stage Cooling

RE4 — Fri, 04 Aug 2023 19:54:42 GMT

@CoolingWizard Yes, sir. The residence is in NW Alabama. The Nest in question was installed in early December 2022 and appeared to work fine during the heating season. My wife, admittedly, likes it cool (cold, to me) in the house, 69F or 70F. Once the cooling season had really kicked in, the conditioned air in the space being controlled by the Nest would rarely reach the set point. According to the metrics the Nest was calling for cooling 23 hours, and a couple of days even 24 hours a day.

That caused me to call an HVAC professional to investigate. He determined the contactor for the 2nd compressor was not being activated. I suggested he look at the wiring for the Nest in question, (he is not a fan of Nest thermostats, I am a fan as I have four of them across two properties, this subject Nest being one of them). I showed him the photo of the wiring for the old American Standard thermostat, he asked if I still had it, I did, he wanted to reinstall it. He did, and the 2nd compressor fired off.

That’s where I am now, … with the old American Standard thermostat reinstalled, and with me wanting the Nest reinstalled … if it can be wired to fire off the 2nd compressor when needed!

Additionally, to follow up on your much appreciated first post:

I will post below a photo of how the wiring flow from the outside unit to the thermostat is run through the different terminal boards. Perhaps you might see why I asked if some of the terminated wires in that terminal box “roll up” to another, (i.e. Y1 and Y2 “roll up” to Y3 (via that relay) on that terminal strip which goes to the thermostat terminal as Y1 … probably as the output from the relay in that terminal box).

I was not able to determine the impact of the different relays in the system. There is one relay on the control board on the compressor unit outside, and the relay you mentioned in your post in the terminal box attached to the outside of the indoor unit, (your suspected sequencer for heating and cooling you mentioned, which is exactly what I think that relay does.)

In your response to my Question #1, you stated my outdoor unit requires a special wire harness for using a conventional thermostat. Would I already have that special wire harness from the use of the original American Standard thermostat, model #32207643-002, Revision A?

In your response to my Question #1, you also state “The control board in the outdoor unit “is want accepts” the second stage cooling call. Did you intend to say the outdoor unit “won’t accept“ the second stage cooling call? If that is the case, is my trying to use a Nest for this application an exercise in futility?

In your response to my Question #2, you state that I, “say I have gas heat.” I certainly feel that this unit does have gas heat as a yellow gas line goes to the unit. I have attached a photo of the inside of the heating/air handler unit for your review. I don’t believe there are any electric heating strips for this unit… but, I could be mistaken about that.

In my Question #5, you state the Nest goes to WiFi to get outside air temperature. That’s good to know. For my own edification, are the terminals on the American Standard thermostat labeled “OT” indeed for “Outside Temperature”? I understand they are not to be used with a Nest.

In my Question #6, I inquired if the terminals on the Nest labeled “ALT STAGE 2” might play a role in the proper wiring of my Nest, thinking that might send the signal to fire off the 2nd compressor. What do you think about that?

At the end of your responses, you asked about the 3 separate thermostat type cables that enter the controller box on the outside of the cabinet. There is one each coming from the outdoor compressor unit, the air handler/furnace unit, and the thermostat. The below photo will hopefully show where each of those wires, in each of those cables, terminate. Please pay no attention to my guesses as to the purpose of those wires, as I was merely trying to figure out what their purpose is. The terminal labels, i.e. B-G3-W3-X2-Y1 … are all good though.

Again, @CoolingWizard , I cannot thank you enough for your time and expertise in helping to get my Nest wired correctly!

Rick

Re: 2nd Gen Nest not activating 2nd Stage Cooling

RE4 — Fri, 04 Aug 2023 20:00:14 GMT

Again, I hope these photos help.

Rick

Re: 2nd Gen Nest not activating 2nd Stage Cooling

CoolingWizard — Sat, 05 Aug 2023 03:50:50 GMT

@RE4 ,

Yes indeed you must have the special wire harness installed. If not those American Standard equipment could only communicate using the digital AccuLink interface. The special wire harness has to be installed in the Air Handler and the outdoor unit. This special wire harness provides the R, W1, W2, Y1, Y2, G and C connections. You furnace has a label on the inside right side, can you get me the model number listed on that label?

Now the question about roll-up of Y1+Y2=Y3 attached to thermostat Y1. Is that the thermostat is all output with the only exception the R wire is input. So the flow is from thermostat Y1->Y3 which splits to Y2+Y1 on terminal strip via the relay.
The relay you describe on the outdoor unit, are called contactors and there should 2 of them. These are high voltage and #1, called CLO, turns on the #1 compressor and the condenser fan motor. The second one when energized by Y2, turns on the #2 called CHI compressor.
There are never electric heat strips inside a gas furnace. There is not place to install them and why would you want to. The ALT Stage 2 is your gas valve stage 2, when activated your gas valve opens the second internal port increasing the BTU output. Typically it increases by 20k BTUs more heat.

As to question #5, the outdoor unit has the outdoor temperature sensor that is a 10k-Ohm thermistor. Both wires of OT are connected to the two wires of the thermistor. They will not be needed. The American Standard thermostat used the temperature data the adjust the defrost cycle time. It allows the thermostat to know when it should activate the auxiliary heat. Since you have dual fuel system, there is no need to have that since the American Standard Gas Furnace you have is not appear to be heat pump knowledgeable. This is why I feel that external relay box is being utilized. And, to confirm this, I need the furnace model number.

When you look at the green circuit board inside the furnace, you see the terminals Y, YLO , W1, W2, O, G, R, B/C, and BK. YLO is stage 1 cooling and Y is stage 2 cooling. W1 is stage 1 gas heat, W2 is stage 2 gas heat. The O is a landing point for the heat pump reversing valve. This tells me your furnace is heat pump smart. Why does have the two stages? This allows the Integrated Furnace Control board (IFC) to adjust the blower speed.

In the thought of education, let us learn about the heating cycle. When the thermostat energizes W1, on the IFC, the imitates the induction fan motor. This motor pulls air into the heat exchanger expelling out the big white pipe you see going outside. After 60-seconds, the IFC checks for a vacuum on VS1, that is the round disc looking things left of the induction fan. If the vacuum is present, it energizes the igniter and activates GAS Valve Stage 1. After 3 seconds, the IFC looks for Flame Ratification Sensor to the positive. If so, the IFC waits for the exhaust temperature to reach 250°F, and then it turns on the Blower Fan at Medium Speed. The IFC sets a timer for stage 2 lockout. When the timer expires, the IFC will accept a call on W2. When W2 is energized, the induction fan motor switches to high speed and the IFC looks for VS2 to be closed. if it is, Gas valve stage 2 is energized and the blower fan speed is increased to high. When the thermostat set-point temperature is met, the thermostat de-energizes W2 and W1 and the IFC turns if the gas valve, and blower reduces to Medium speed and runs for few minutes more to get more heat from the heat exchanger into the living space.

Now the cooling cycle. When the thermostat energizes Y1, the IFC turns on the Blower Fan on Medium High and sends YLO power to the outdoor unit energizing contactor #1 and thus compressor #1. There is a stage 2 lockout timer that waits 90-seconds before allowing Y can be acted upon. If the thermostat energizes Y2, it is connected to Y at the IFC, the IFC increases the blower speed to High, and the second contactor is energized thus starting compressor #2.

That relay box on the outside of the ducts, has a label on the cover, can you get me screen shot of that label?

I hope that this information helps you to understand your HVAC system.

AC Cooling Wizard

Re: 2nd Gen Nest not activating 2nd Stage Cooling

CoolingWizard — Sat, 05 Aug 2023 00:26:19 GMT

@RE4 ,

is the first picture the outdoor unit?

AC Cooling Wizard

Re: 2nd Gen Nest not activating 2nd Stage Cooling

RE4 — Sat, 05 Aug 2023 04:07:40 GMT

@CoolingWizard , thank you for lending your expertise to help me understand my HVAC system!

Sorry, I am not clear as to whether I “now have”, or whether I “will need to obtain” the special wiring harness you mentioned.

Below you will find the photo of the label inside the upper half of the Furnace / Air Handler cabinet. As well a photo of the labels on the cover of the relay / terminal box attached to the duct panel.

It’s interesting, and makes sense that the signals travel from the thermostat back to the relay / terminal board and the furnace / air handler board. I should have realized that…. So, instead of the different terminals “rolling up” as I surmised, they actually “roll out” to the rest of the system. Thanks for helping me understand that.

The HVAC professional that came out and reinstalled the American Standard thermostat, showed me the two contactors you mentioned. He showed me that the #2 compressor contactor engaged indicator was not extending from its case, like the #1 compressor contactor was.

I certainly misspoke when said there were two Nest terminals I did not use… the ALT STAGE 2, and the RH. I think you caught that, I did not use the “*” (asterisk), and the RH terminals. In the image of the wired Nest, I noticed the ALT STAGE 2 indicator on the Nest screen was greyed out and not green. Is that indicative of a problem in my wiring … besides the problem that caused the #2 compressor to not be activated?

In your paragraph in which you detail the furnace circuit board terminals, you state that W1 and W2 are both gas heat stages. That leaves X2 to be Heat Pump heat … is that correct?

Which of the wires on the Nest install were correct, and which ones do I need to change in order to activate the #2 compressor?

You have been so generous to share you knowledge with us, I cannot thank you enough!

Rick

Re: 2nd Gen Nest not activating 2nd Stage Cooling

RE4 — Sat, 05 Aug 2023 04:14:44 GMT

I hope these are the photos you requested.

Rick

Re: 2nd Gen Nest not activating 2nd Stage Cooling

CoolingWizard — Sat, 05 Aug 2023 06:26:40 GMT

@RE4 ,

Ok, I have reviewed the documentation of the Heat Pump kit. (the relay box) and the manual of the furnace. Bottom line, the heat pump kit is not needed for your system. The fact that the Nest Learning Thermostat is far more intelligent and the fact that your Furnace has a heat pump IFC, the heat pump kit is not needed. Perhaps it was part of an older furnace or something. You do not need the special wire harness because it’s already installed in your outdoor unit. Below is the wiring schematic of your furnace air handler and a 2-stage heating and a 2-stage cooling application.

You feel up to rewiring everything to make it all work properly?

Technically you can wire up a gas furnace so as to act like auxiliary and emergency heating for a heat pump. This is highly not recommended however. So for the Nest Learning Thermostat, in a duel fuel setup, the 2-stage gas furnace would be wired to W1 and W2. You would have to make some cost calculations to determine at what temperature do we turn off the Heat Pump and switch the heating to Gas Furnace. The variables to consider is the cost of the gas and the kilowatts of heat produced compared the kilowatts of electricity used by the heat pump. For a heat pump, there comes a point I call the point of diminishing return. The colder it gets the less efficient the heat pump becomes. At about 22°F, your particular heat pump will start to become less efficient and at 10°F it simply spends more time in defrost mode than in heating mode. Some homeowners prefer the gas heat because it feels better but it drys the air and a humidifier is beneficial to have. The heat pump heat feels moist or even cooler than gas.

AC Cooling Wizard

Re: 2nd Gen Nest not activating 2nd Stage Cooling

zoeuvre — Tue, 08 Aug 2023 15:29:04 GMT

Hi folks,

@RE4, thanks for reaching out, and I'm sorry to hear about the situation. I want to check if you managed to see the response above. Please let us know if you still have questions or concerns, as we'll be willing to assist you more.

I appreciate your help, @CoolingWizard.

Best,

Zoe

Re: 2nd Gen Nest not activating 2nd Stage Cooling

RE4 — Thu, 10 Aug 2023 01:42:13 GMT

@CoolingWizard

So sorry I have been absent for a few days, I’m now able to devote some more time to this thermostat, … with your able assistance!

Since the system seemed to work properly before the Nest install, I am hesitant to remove the Heat Pump Kit from the system since it has an airflow switch and a relay with 16 terminals that must do all kinds of magic, depending on the functions in use.

Due to your very helpful posts, I have made a couple of wiring changes and a couple of configuration changes.

We now have both Heat Pump stages working correctly for both cool and heat. We also have the Natural Gas alternate heat working for Stage 2 on the * (asterisk) terminal.

I have not been able to get the Natural Gas - Stage 1 heat to fire off. I cannot even get the fan for that selection to run. When I test the Alternate Stage 2 heat, I get all three burner tubes firing off and the heat output at the nearest duct vent is over 100 degrees F. I am supposing that’s because the Furnace’s W1 & W2 terminals are jumpered?

I think I have figured out where the problem lies, but I don’t want to make any changes without running it by you first.

Here’s the current situation for the Alt Heat wiring:

Thermostat W1 WHITE wire to the Heat Pump Kit terminal W3.

Thermostat W2/AUX is empty.

Thermostat * (asterisk) BLACK wire to the Heat Pump Kit terminal X3.

Heat Pump Kit terminal W1 WHITE wire to Furnace Board W1, which is jumpered to W2.

Heat Pump Kit terminal X2 WHITE wire to outdoor compressor unit BLACK wire. (The schematic shows it goes to two optional ODTs, and is labeled as X2.)

I believe the jumper needs to be removed from the Furnace Board W1 & W2 terminals leaving that WHITE wire connected to the W1 terminal. And, the unused BLACK wire at the Furnace Board needs to be connected to the Furnace Board W2 terminal, with the other end to be connected to the Heat Pump Kit terminal X2?

1. The thing I am unsure about is what the BLACK wire at the compressor unit does with respect to the Nest’s * (asterisk) terminal?

2. And, can I have the Furnace’s W2 terminal connected to the Heat Pump Kit’s X2 terminal … “along with” the WHITE wire that connects to the compressor unit’s BLACK wire?

Am I barking up the wrong tree here?

Rick

Re: 2nd Gen Nest not activating 2nd Stage Cooling

CoolingWizard — Thu, 10 Aug 2023 03:13:12 GMT

@RE4 ,

Lets talk about how your gas furnace works in terms of sequences.
Call for first stage W1 and second stage W2 heating.
W1 thermostat contact close, signaling the control module to run its self-check routine. After the control module has verified that the 1st stage pressure switch contacts are open and the limit switches contacts are closed, the induction draft blower will be energized on low speed.

As the induced draft blower comes up to speed, the 1st stage pressure switch contacts will close and the igniter warm up cycle will begin. The igniter will heat for approximately 20 seconds, then the gas valve is energized in 1st stage to permit gas flow to the burners. The flame sensor confirms that the ignition has been achieved within four seconds of the ignition trial period.

As the flame sensor confirms, the ignition has been achieved, the delay to fan on begins timing and after approximately 45 seconds the indoor blower motor will be energized at the low speed and will continue to run during the heating cycle.

Call for 2nd stage:

W2 thermostat contact closes signaling a call for 2nd stage heat. After 30 second delay, the induced draft blower will be energized on high speed and the second stage pressure switch contacts will close. The gas valve is energized in 2nd stage and the indoor blower motor switches to high speed.

If you want to see Stage 1 in action, disconnect the jumper between W2 and W1. Then turn on the heat. The problem is if you want to have the Nest thermostat control W2, you need to change some wiring in the Heat Pump Kit.

AC Cooling Wizard

Re: 2nd Gen Nest not activating 2nd Stage Cooling

RE4 — Thu, 10 Aug 2023 03:44:05 GMT

@CoolingWizard

Thank you for that explanation! That certainly helps my understanding of what’s going on when Aux Heat is called for.

Can you tell me:

What the black wire at the outdoor compressor unit does, and how it relates to the the * (asterisk) terminal on the Nest?

And, can I connect the Furnace W2 wire to that black wire at the compressor and to the Nest’s * (asterisk) terminal?

Rick

Re: 2nd Gen Nest not activating 2nd Stage Cooling

CoolingWizard — Thu, 10 Aug 2023 22:57:45 GMT

@RE4 ,

I need to show you the Heat Pump Kit and it’s typical wiring.

Your Stage 1 and Stage 2 Heat is the heat pump. Your stage 3 Heat is the W that goes to your oil burner. When the thermostat energizes the W wire, this is what causes the K1 Relay to to engage. When that happens power is sent to the W wire to the oil burner to start the heating cycle. At the same time this disconnects stage 1 of the heat pump. Notice the brown wire of Y2. This second stage cooling is wired direct between the thermostat and the heat pump.

AC Cooling Wizard

Re: 2nd Gen Nest not activating 2nd Stage Cooling

CoolingWizard — Fri, 11 Aug 2023 00:37:09 GMT

@RE4 ,

The Heat Pump Kit that you have is designed to integrate a gas furnaces with a heat pump. It is a hybrid solution that is no longer needed with the advancement made in programable and intelligent thermostats which essentially preforms the same function. As I previously stated, with the Nest Thermostat, you no longer need to use the Heat Pump Kit. The thermostat cable going to the outdoor heat pump unit, needs to disconnected from the heat pump kit, the cable routed to the furnace. The cable between the furnace and the heat pump kit, needs to be disconnected and removed. With the cable going to the heat pump routed to the Furnace cabinet. You will attach the wires as follows:

Yellow, attach to YLo this is Stage 1 Cooling, stage 1 Heat Pump Heat

Brown, attach to Y This is stage 2 Cooling, Stage 2 Heat Pump Heat

Orange, attach to O, Heat Pump Reversing Valve.

Green, Not connected

White, not connected

Black, not connected

Red not connected

Blue, attach to C

Take the cable from the thermostat disconnect it from the Heat Pump Kit and route it to the furnace.

Attach the wires as follows,

Red, attach to the R

Blue, Attach to the C

Yellow, Attach to Y-LO

Brown, Attach to Y

Orange attach to O

Green, attach to G

White attached to W1

Black, attach to W2, remove the white jumper between W1 and W2.

Now for the Nest Thermostat, you will set this up as a Duel Fuel, Heat Pump, Forced Air

The wires are attached as follows

Red, to Rc

Green, to G

Blue, to C

Yellow to Y1

Brown to Y2,

Orange, to OB

White, to W1

Black, to W2

Ready to assist you with the reconfiguration,

AC Cooling Wizard

Re: 2nd Gen Nest not activating 2nd Stage Cooling

RE4 — Fri, 11 Aug 2023 01:08:26 GMT

@CoolingWizard

Thank you SO much! I will get on that first thing tomorrow morning. I will report back...

Rick