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Nest Thermostat Wiring separate Heat and AC. Need Help Please.

ffrezza
Community Member

Hello folks and thank you so much in advance. I am reading and reading and about to call it quits.

I am looking to add two Google Nest Thermostats to a two-zone heating system and separate AC with no C wire.

The house has a boiler (forced hot water with baseboards throughout the entire house) installed in the basement and an a/c unit installed the attic. The Boiler is an older Utica Model MGB125HD with
two taco styles zone controllers ( I think that's what they are called).


The basement thermostat (zone 2) is heat-only (Red connected to RH and White Connected to W wires. There's a small jumper wire between RH and RC).
Current Thermostat is a RITEMP Model 8022C. For a replacement I purchased a Google Nest Thermostat (Snow model). Is it possible to use this Thermostat in the basement with this configuration (heat only)? The thermostat says it comes with two 1.5V AAA batteries. Does this mean I do not need a C wire for this set up or can I even use this thermostat here?


The Main floor or first floor thermostat (zone 1) has separate heat and a/c (which is using the Rc terminal).
Current Thermostat is a Honeywell CT3300A1009. Purchased a Nest 3rd Gen Learning Thermostat, Item T3007ES, as a replacement.
Here the Red and White wires come from the boiler in the basement for heat while the Red Wire (Rc), Yellow (Y), and Green (G) come from the A/C unit in the attic.
My understanding is that I may need a C wire here so I purchased a 24V external transformer which I am planning to wire into an Existing Electrical box in the attic, directly above the 2nd floor Thermostat
(and near the AC unit) and easy to feed to thermostat.  I plan on feeding a two wire thermostat wire directly from the transformer to the the 3rd gen thermostat on the first floor (zone 1) but in reading the different configurations I am getting more and more confused.
My understanding is that the two wires coming from the 24V transformer would go to C and RC however as mentioned, the main-floor thermostat (zone 1) has both heat and a/c. The a/c is already using the Rc terminal.
If the White wire from the boiler (from heat) goes to W1 and Red wire (from heat) goes to RH. Then Yellow (from A/c) goes to Y1, Green (from A/c)goes to G, and Red (from A/c) goes to RC how
can I use an external 24v transformer to provide the missing C? The transformer has two wires. One would go to the C connection but where does the other wire connect to?

 

Here is what I have already purchased.

Nest 3rd Gen Smart Thermostat: https://www.amazon.com/T3007ES-Programmable-Thermostat-Generation-Enabled/dp/B07JYVYKRS/ref=sr_1_15?...

Nest Nest Thermostat(Snow):https://www.amazon.com/Google-Nest-Thermostat-Smart-Programmable/dp/B08HRPDYTP/ref=sr_1_2?keywords=N...

24V Transformer (for C wire): https://www.amazon.com/gp/product/B08LNVXL2R/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1


Zone 2 Basement: Heat Only (Hot Water).
One Thermostat Wire with:
White (w) to W
Red (R) to RH
Jumper wire Between RC and RH

Zone 1 First Floor: Separate Heat (Hot Water in Basement) and A/C Unit (in Attic) .
Two Thermostat Wires

One for Heat With 2 wires:
White (w) to W
Red (R) to RH

One for A/C with three wires:

Yellow (y) to Y
Green (G) to G
Red (R) to RC
The Ac cable also has a Brown, Blue, and White wire but cut off and not connected in the thermostat as well as upstairs at the AC unit.
The AC Unit in the attic has three thick wires. Red from thermostat connected to Red A/C unit, Green from thermostat connected to Green A/C unit, and Yellow from thermostat connected to Blue A/c unit. All connected with wire nuts.

 

Thank you sooo much in advance.

Frank

1 Recommended Answer

ffrezza
Community Member

Here is an update. Contacted  google nest rep on chat. They have offered no help.  Here is an update. Thanks for nothing I guess.

 

Blake -  For zoned systems that require thermostat damper control aren’t compatible with Nest thermostats, while other zoned systems may need a C or common wire, or the Nest Power Connector, to be compatible.
Blake 3:08 PM
I strongly recommend you to contact a nearby Nest Pro or HVAC technician for installation.
Is there anything else I can help you with today?
Blake · 3:08 PM
nope. have a great day.
3:08 PM
B
Thanks for contacting Google! It was a pleasure chatting with you. Have a great day!

View Recommended Answer in original post

5 REPLIES 5

ffrezza
Community Member

Here is an update. Contacted  google nest rep on chat. They have offered no help.  Here is an update. Thanks for nothing I guess.

 

Blake -  For zoned systems that require thermostat damper control aren’t compatible with Nest thermostats, while other zoned systems may need a C or common wire, or the Nest Power Connector, to be compatible.
Blake 3:08 PM
I strongly recommend you to contact a nearby Nest Pro or HVAC technician for installation.
Is there anything else I can help you with today?
Blake · 3:08 PM
nope. have a great day.
3:08 PM
B
Thanks for contacting Google! It was a pleasure chatting with you. Have a great day!

Indrestudios
Community Member

Hello - did you ever resolve your Nest connection issues?  I’m in the same boat with separate heat & AC units - have yet to get the Nest connected to the AC system - same wiring as you for AC

Green Wire - G
White Wire - Y
Red Wire - RC

ffrezza
Community Member

Nope. My thermostats are still in their boxes. I have decided not to install thrr we n until I get a clear picture of how to install them correctly. This is totally ridiculous. Spent money to buy their products snd they can’t even help you. Last time I will purchase any google product. I will probably donate what I have already purchased and buy new ones from a company who supports their product. 

Indrestudios
Community Member

Frustrating for sure.  Wishing you luck...

Snelson2501
Community Member

Hello, I have the same setup except I have 3 zones. I have had mine wired and running with the Nest Learning 3rd Gen and two Nest E's for 2 yrs, with one only one slight hiccup, the ac.

I have the ac wires connected just as you wrote but I have my heat wires switched around. So my red goes to W and my white goes to Rh. 

I have the learning thermostat on the main control that does both the heat and the ac. And the Nest E thermostats on the other two zones. The heat works great! No issues at all. 

When I use the ac in the summer the main Nest will not hold a charge, probably because I have no c wire. I also have a blue wire that was cut and have tried putting that in the C spot and it doesn't work. So every few days, depending on how much the ac runs,  I have to remove the Nest base and manually charge it for about an hour. Then I put it back on and we're back in business. A bit of a pain but I haven't gotten around to fixing it yet.

Hope that helps!!