Replace thermostat with a NEST ?

[sonofcy]

2018 Montana 3811MS with heat pump, A/C and gas heat.

I would like to replace the stock thermostat with a Nest thermostat but the 3 wires are not labelled. Does anyone know where I could get reliable info on which wire is which?

[chuckster57]

Quick check of nest specs say it works with 24V HVAC, RV is 12V.

Wires should be 12V+
Ground
Signal to control panel ( located in AC return plenum)

[sonofcy]

Originally Posted by chuckster57

Quick check of nest specs say it works with 24V HVAC, RV is 12V.

Wires should be 12V+
Ground
Signal to control panel ( located in AC return plenum)

I think it is obvious that the 3 wires 2 of which are + and - 12v are not enough to control a gas furnace, fan, A/C and heat pump. Those wires go to a 'black box' that controls the HVAC equipment and will likely have the standard connections. The trick will be locating the black box but as I am writing this I just remembered I bought one of those inspection cams the other day so I will give that a try.

[chuckster57]

Control box is at the AC. The wires will be obvious. You have to remove the ceiling plenum (grill) to see it.

[sonofcy]

Originally Posted by chuckster57

Control box is at the AC. The wires will be obvious. You have to remove the ceiling plenum (grill) to see it.

Not that kind of A/C, there are a total of 4 cold or warm air outlets a long way from the thermostat. The wires run down so I will have a look with the inspectoscope tomorrow.

[chuckster57]

Not the outlets. Unless you have a “whisper quiet” system with returns on the edges of the ceiling, the return will be where the main AC unit is and you will need to remove the grill that has the filter in it.

[sonofcy]

Originally Posted by chuckster57

Not the outlets. Unless you have a “whisper quiet” system with returns on the edges of the ceiling, the return will be where the main AC unit is and you will need to remove the grill that has the filter in it.

Yes, it's a whisper quiet.

[brad2388]

Nope it wont work.

The rv thermostat is on a communication cicuirt and all talk to each other. Includeing the gas heater.


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[sonofcy]

Originally Posted by brad2388

Nope it wont work.

The rv thermostat is on a communication cicuirt and all talk to each other. Includeing the gas heater.


Sent from my iPhone using Tapatalk

Given that there are only 3 wires on the thermostat I figured it was just a comms circuit, I am going to try to find the black box it talks to and see if it has 'standard' HVAC wiring.

[brad2388]

Originally Posted by sonofcy

Given that there are only 3 wires on the thermostat I figured it was just a comms circuit, I am going to try to find the black box it talks to and see if it has 'standard' HVAC wiring.

Its not.
The boards are relay based and each board has its own logic to it.
If you have the dometic nxt units you can take the top off and if your looking at the front of the ac unit the control boxes are on the left side.

On each control box theres a set of dip switches to select what zone it is and if it has heat strips or a heat pump option.



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[sonofcy]

Originally Posted by brad2388

Its not.
The boards are relay based and each board has its own logic to it.
If you have the dometic nxt units you can take the top off and if your looking at the front of the ac unit the control boxes are on the left side.

On each control box theres a set of dip switches to select what zone it is and if it has heat strips or a heat pump option.



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That doesn't sound encouraging. The little info I have found includes a photo of the LCD thermostat and it is clearly wired to a control box. I even downloaded a complete schematic but I don't yet know if it is the same model. Will get back to it Tuesday, too tired now and busy out of town tomorrow.

[chuckster57]

I’m learning something new here too. Haven’t had much exposure to the 10 button thermostats. We just started carrying Heartland and I think they have them.

[sonofcy]

Originally Posted by chuckster57

I’m learning something new here too. Haven’t had much exposure to the 10 button thermostats. We just started carrying Heartland and I think they have them.

Mine is NOT a 10 button, just a mode selector and an up/down pad. It's capacitive and a pita to operate, it changes from C to F on a whim and will continue to increase or decrease after you remove your finger. Typical RV crap.

[chuckster57]

So you have the 3 button. LCD screen, up and down buttons on right and a mode button on the left?

If you have more than one unit on the roof, I’m not seeing how it can choose a “zone”. It can be a bit temperamental, but once you understand how to “touch” it, it should be good.

[sonofcy]

Originally Posted by chuckster57

So you have the 3 button. LCD screen, up and down buttons on right and a mode button on the left?

If you have more than one unit on the roof, I’m not seeing how it can choose a “zone”. It can be a bit temperamental, but once you understand how to “touch” it, it should be good.

2 units. Main is A/C and heat pump. The bedroom is just A/C although we were under the impression it was also a heat pump. It has its own LCD thermostat. It has fan, A/C and furnace but as far as I can tell the furnace setting does nothing. The main unit is fan, A/C, furnace and heat pump.
Love the heat pump, no condensation issues.

[chuckster57]

Ok. That’s what I see a lot of. The main thermostat will have:
Fan
Cool
Heat pump
Furnace
On the left side.
Working on a new SunSeeker class C with this. I’ll see what I can dig up.

[MikeD3534]

I'm wanting to do the same thing (install a wifi thermostat). Please keep us posted. I have a feeling that the RV industry will have to come up with a "nest-like" product.

[ctbruce]

Originally Posted by sonofcy

2 units. Main is A/C and heat pump. The bedroom is just A/C although we were under the impression it was also a heat pump. It has its own LCD thermostat. It has fan, A/C and furnace but as far as I can tell the furnace setting does nothing. The main unit is fan, A/C, furnace and heat pump.
Love the heat pump, no condensation issues.

Open the bedroom unit up and see if the heat strip is connected.

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[sonofcy]

Originally Posted by ctbruce

Open the bedroom unit up and see if the heat strip is connected.

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There is nothing to see inside of these thermostats, they do not have conventional wiring

[ctbruce]

Originally Posted by sonofcy

There is nothing to see inside of these thermostats, they do not have conventional wiring

The air conditioner not the thermostat. The heat strip is in the AC unit.

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