topic Re: VisionPRO IAQ to Nest Learning Thermostat in Nest Thermostats

VisionPRO IAQ to Nest Learning Thermostat

earthtraveler5 — Wed, 02 Nov 2022 16:50:46 GMT

I am wanting to replace a VisionPRO IAQ with a Nest Learning Thermostat.

Is this possible?

Please let me know if this can work.

Here is a list of my HVAC hardware.

Name	Company	Model Number	Manual
Heat Pump	Goodman Manufacturing	GSH130481A A	https://www.manualslib.com/manual/1539089/Goodman-Gsh130181a-Series.html#product-GSH130481A%20Series
Furnace	Goodman Manufacturing	GMS81405DNA	https://www.manualslib.com/manual/738470/Goodman-Gms8.html
Thermostat	Honeywell	VisionPRO IAQ	https://www.manualslib.com/download/711761/Honeywell-Visionpro-Iaq.html
Smart thermostat	Nest (Google)	Nest Learning Thermostat, 3rd Generation	http://support-assets.nest.com/images/pro-faq/Nest-Pro-Installer-Guide.pdf

Re: VisionPRO IAQ to Nest Learning Thermostat

CoolingWizard — Wed, 02 Nov 2022 19:34:10 GMT

Earthtraveler5,

You can convert from the IAQ to the Google Nest. There might be some Sensor Wires (S1/S2) being used you will not need with the Nest Learning Thermostat. You have heat pump system with a Gas fired forced air furnace. The question is which is the primary heat? The Heat Pump or the Gas Furnace? Your gas furnace can act as the heat pump axillary/emergency heat and this is most likely your current setup. Alternatively the system can be set up as the Heat Pump only does Air Conditioning cooling and your Gas Furnace is your heating system. Your Heat Pump needs the O/B wire energized to switch the reversing valve to Heating mode.

Ken, The AC Cooling Wizard

Re: VisionPRO IAQ to Nest Learning Thermostat

earthtraveler5 — Wed, 02 Nov 2022 19:40:07 GMT

Thank you Ken.

My big question is where to connect the W3 / AUX2 wire and the humidifier wires. According to the
Here are some pics.

Re: VisionPRO IAQ to Nest Learning Thermostat

earthtraveler5 — Wed, 02 Nov 2022 19:41:44 GMT

Thank you Ken.

My big question is where to connect the W3 / AUX2 wire and the humidifier wires.

According to the doc: Nest Learning Thermostat Pro Installation & Configuration Guide, they both need to go on the * on the Nest.

Here are some pics.

Re: VisionPRO IAQ to Nest Learning Thermostat

CoolingWizard — Wed, 02 Nov 2022 20:05:35 GMT

Earthtraveler5,

we need make sure that 5 wires are in the thermostat wire going to the thermostat. Your IAQ is using digital communications with he EIM. It is the EIM that controls the equipment.

The EIM has W1:O/B wire goes outdoors to your heat pump Reversing Valve. The W2 wire goes to the Furnace to initiate Gas Heat which is the Auxiliary Heat. W3 in the EIM goes to something I cannot see perhaps emergency electric heat strips? it also looks like you have a humidifier?

I feel that is going to need a Nest Pro working for an HVAC company to rewire your equipment to remove the EIM and get more conductors to your thermostat. Currently there are not enough conducting wires going to the thermostat location to handle the primary and secondary heat and the W3 and the humidifier

Ken, The AC Cooling Wizard

Re: VisionPRO IAQ to Nest Learning Thermostat

earthtraveler5 — Wed, 02 Nov 2022 20:58:23 GMT

There are 8 wires in the cable going from the EIM to the thermostat.
It looks like W1 & W2 both go to the heat pump. W3 goes to the furnace.
Yes, there is a humidifier. There are wires to both Hum 1 & 2.
I did have a "Nest Pro" come out and he did say it was incompatible. But, I'm not so sure I trust him. I am looking for more information to see if it might work.

Re: VisionPRO IAQ to Nest Learning Thermostat

CoolingWizard — Wed, 02 Nov 2022 21:46:06 GMT

Chances are that Nest pro who showed up was not an HVAC professional technician. We can use the eight wires to go to the nest thermostat and it will control the heat pump, gas furnace, humidifier, and whatever the second stage heat was that hooked up on W3 of the EIM.

The wires it will be used by the nest learning thermostat third generation are:

Rc - Power In

C - Power Common

Y - Compressor Contactor

O/B - Heat Pump Reversing Valve (primary Heat)

W1 - Auxiliary Heat stage 1, gas furnace

W2 - Auxiliary Heat Stage 2, unknown

G - Blower Fan

* - Humidifier

Ken, The AC Cooling Wizard

Re: VisionPRO IAQ to Nest Learning Thermostat

earthtraveler5 — Thu, 03 Nov 2022 14:34:15 GMT

Thank you Ken.

Few more questions:

1. It looks like OB and Aux both go to the heat pump. W3 looks to go to the furnace. Attaching clearer pics of the wiring on the right of the EIM (Equipment Interface Module) as well as another pic of wiring for the EIM / HP / Furnace. Does this look / sound correct to you? Also, the green highlighted area of the annotated image of the wiring diagram for the EIM has been my biggest uncertainty. But, you're helping to clarify it for me.

2. There are two Humidity wires as shown in the yellow highlighted section. Looking at the left pic of the EIM, it looks like H1 also goes to C. So, my guess is that the red wire goes to C and the white wire goes to *. Does this sound correct?

3. I have attached annotated screenshots of both the Nest wiring diagram and the EIM wiring diagram with numbers of what I understand of which wire on the EIM goes to which terminal on the Nest. Does this look correct to you?

Please let me know.
Thanks

Re: VisionPRO IAQ to Nest Learning Thermostat

CoolingWizard — Thu, 03 Nov 2022 18:52:30 GMT

Earthtraveler5,

I guess it’s time now for the ugly truth, lol.
Your Goodman heat pump has a reversing valve that when not energized the system is in heating mode. To get AC cooling mode you have to energize the reversing valve on the OB terminal. When your heat pump is in heating mode, the defrost control board temperature sensor closes at 31°F, that is sensing ice on the coil, and that initiates the defrost cycle and the defrost control board then sends a control call on the W2 wire of the outdoor defrost controller to the indoor unit to activate the auxiliary heating, in your case the gas furnace. In systems that do not have gas heat they have the indoor coil and usually 15kW to 45KkW of electric heating strips that are the auxiliary/emergency heat.
You sort of have the best of two worlds, depends if gas or electricity is less expensive per equivalent BTU of heat to heat your house. The problem is a normal thermostat does not have the intelligence to make that decision for you. In the case of the Nest, and most smart thermostats, when it is programmed as controlling a heat pump it can only assume that there is auxiliary and or emergency heating. Furthermore, the thermostat considers the heat pump as the primary mode of heat. As a homeowner you will only be able to get gas heating when you place your thermostat in emergency heat or auxiliary heat mode. Otherwise the heat pump will be your primary motive heat and it will only signal the gas to come on when the outdoor unit enters defrost cycle.
The outdoor unit connection points are only C, Y, R, W2, G. This picture below, from the installation manual, shows the Heat Pump Low Voltage Junction Box.

Now let’s talk about the humidifier, the humidifier has as you understood correctly, two wires one is common and one is control voltage. The humidifier is a self-contained unit that has a humidistat and a setting that the homeowner can place for the desired humidity level during heating periods. The most desired heating percentage is 50% typically. When the control wire is activated it signals to the humidifier to turn on and using the humidistat will measure the humidity and if it’s below the desired level it will activate the humidifier function. We only need to send one wire from the thermostat there and that will be the red wire and the white wire will be connected to the common in the furnace.

The wires you have numbered will need some adjustment, #5 wire will not be used, the #6 (W2) from the furnace and outdoor unit will go to the W2(#5) position in the thermostat. All the other wires, as you deduced are correct.

when you go through the Nest online configuration tool you will list the wires that on your old thermostat are as follows. Rc, C, Y1, W2, O/B, G, HUM.

Ken, The AC Cooling Wizard

Re: VisionPRO IAQ to Nest Learning Thermostat

earthtraveler5 — Sat, 05 Nov 2022 15:47:49 GMT

Thanks again Ken.

I have one more clarification question. So my annotated #5 (W1) terminal on the Nest is not used?

Instead, the two wires from the EIM, annotated #5 (W2/AUX) and #6 (W3/AUX2) are combining into the Nest at terminal #6 (W2/AUX).

Is this correct?

Re: VisionPRO IAQ to Nest Learning Thermostat

CoolingWizard — Sun, 06 Nov 2022 02:31:43 GMT

earthtraveler5, the Aux 3 in your system goes somewhere I cannot see in your photos. What is marked as Aux 2 on the EIM should be W1 on the nest, the AUX 3 would be either W2 or Emergency Heat.

Ken

Re: VisionPRO IAQ to Nest Learning Thermostat

earthtraveler5 — Sun, 06 Nov 2022 02:52:27 GMT

Hi Ken,

In this photo, OB (4) is from the heat pump.

AUX (5) is also from the heat pump.

AUX2 (6) is from the furnace.

So, 4 goes to OB. 5 goes to W1. 6 goes to W2?

Where is emergency heat on the Nest? Is that W2 or somewhere else?

Re: VisionPRO IAQ to Nest Learning Thermostat

CoolingWizard — Sun, 06 Nov 2022 03:36:27 GMT

That is manufacturer sample set up. On your EIM, the Green, White, and Yellow wires on the top right, are connected on the outdoor unit are they not?

Ken

Re: VisionPRO IAQ to Nest Learning Thermostat

earthtraveler5 — Sun, 06 Nov 2022 04:34:08 GMT

Yes, correct.

The yellow, green, and white wires that go to the top left go to the outdoor unit. The yellow, green, and white wires that go to the bottom left go to the furnace.

Re: VisionPRO IAQ to Nest Learning Thermostat

CoolingWizard — Sun, 06 Nov 2022 05:27:36 GMT

The green wire on EIM G, going to the furnace is the Blower Fan Motor control. The EIM Y/Y2 yellow wire controls the Compressor outside. It also signals the furnace to turn on the blower when the compressor is turned on. I figure the EIM White W3/AUX2 going to the furnace is connected to W on the furnace control board.

We need to remember that the EIM, is a fully programmable switch controller. Each of those connections on the right, can be programmed for anything that is needed in a system. With outdoor temperature sensor connect to S1/S2, the EIM can be programmed to turn off the Heat Pump and turn on the Gas Furnace when say the outside ambient air temperature drops to say 10°F. Basically, at -4°F ambient the Heat Pump looses heating capacity.

What we know is the Goodman Furnace only has R,C,G,Y,W connections on the Furnace control board. The O/B is not on the Furnace control board. On the outdoor unit there are R,W2,Y, OB, and C. If I can find the time tomorrow I will try to draw up a wiring schematic for the Nest to the Furnace, Furnace to the outdoor unit to help you see it with he EIM not in the picture.
Ken, The AC Cooling Wizard

Re: VisionPRO IAQ to Nest Learning Thermostat

earthtraveler5 — Sun, 06 Nov 2022 19:15:36 GMT

That would be very helpful. Thank you very much for all your help.

Re: VisionPRO IAQ to Nest Learning Thermostat

CoolingWizard — Mon, 07 Nov 2022 06:25:41 GMT

Here is a picture I created to kind of show you how the wires will run from unit to unit to unit I hope this helps you understand how to wire it.

Re: VisionPRO IAQ to Nest Learning Thermostat

aatienza — Tue, 08 Nov 2022 02:38:49 GMT

Hey earthtraveler5,

Checking in — we hope you've got the answer you're looking for. Let us know if you have more questions in mind.

I appreciate the help, CoolingWizard.

Thanks,
Archie

Re: VisionPRO IAQ to Nest Learning Thermostat

earthtraveler5 — Tue, 08 Nov 2022 03:06:08 GMT

CoolingWizard

You're awesome!! Thanks!!

I wish I could give you that Nest Pro payment.

Here it is. Everything tested good. How does it look?

The wiring is a bit of a mess but I think it's all connected correctly.

Re: VisionPRO IAQ to Nest Learning Thermostat

earthtraveler5 — Tue, 08 Nov 2022 03:11:29 GMT

I think I have to connected and working well. Much CoolingWizard!