HVAC wiring for thermostat and how they work

[bob]

I am looking at replacing the thermostats in my Solitude with automated relays, and I am trying to find how the thermostat works... I know what the wires on the back of the thermostat are (AirExcel), i just need to understand the logic - when you want fan, you put 12vpos to the fan high wire, etc - correct? To turn on the heatpump, i add power to the heat pump wire and the compressor as well?

I found this document which lays it out I think - https://www.manualslib.com/manual/16...?page=2#manual but I want to make sure I understand it I figured out the call, etc - but creating the logic with the gas + heat pump looks interesting...

I know, when you have to ask these basic questions maybe you shouldn't be messing with such things, but in my attempts to automate my RV, I want to see if this is possible...

Thanks!

Bob

[Country Campers]

From my understanding that is exactly how they work. The only thing I think is different from your thinking is that it may not be 12 v dc sent to the appliance, it may be less voltage like 5 v dc, you would have to check the output wires or have a schematic of the thermostat that would provide that info. The thermostat sends this voltage, called a signal, to the appliance circuit board which is then interpreted and the command is put forth in motion.

Easy Peasy...

Brian

[bob]

Thanks, that's what I thought. I looked at the logic on how the heat pump works and that is going to be the bigger pain in the tail. I think I am gong to leave that toward the end, that logic is going to be a longer project lol.

[Jlawles2]

The Heat Pump is probably AC plus one more circuit for a reversing valve. If you can get everything else working and assuming it's all 12VDC controls, you might be able to wire the heat pump relay with a diode to the AC control side so the heat pump send the signal to both the compressor and the reversing valve while the diode prevents the AC demand from sending signal voltage to the reversing valve.

That makes sense in my mind hopefully it makes sense to you.

[ncitro]

I am pretty sure the furnace itself is just clean contacts. I believe if you short the two wires going from the thermostat to the furnace it turns on and runs.

The AC I think operates as you suspect and I believe it is 12v vs a residential thermostat which is 24, one of the reasons we can't easily switch to a residential thermostat that's powered by the HVAC equipment.

[bob]

For those interested, the way the heat pump works is painful See the process here in the AirExcel manual (this of course assumes you are using the AirExcel thermometer)

https://www.manualslib.com/manual/16...?page=2#manual

I think i am going to go down the path of fitting an EcoBee thermostat (especially since it has remote temp sensors, hopefully I can use that as a way to get around all the thermostats being in one place) instead of trying to go crazy with a custom build, and I don't really use the heatpump so I will likely leave that out of the equation for now...

[howson]

For those interested, the way the heat pump works is painful See the process here in the AirExcel manual (this of course assumes you are using the AirExcel thermometer)

https://www.manualslib.com/manual/16...?page=2#manual

I think i am going to go down the path of fitting an EcoBee thermostat (especially since it has remote temp sensors, hopefully I can use that as a way to get around all the thermostats being in one place) instead of trying to go crazy with a custom build, and I don't really use the heatpump so I will likely leave that out of the equation for now...

Bob,
I saw this Coleman adapter at the rally. No personal experience with the unit, but thought you might find it interesting. https://parts.unitedrv.com/products/...enter-8330-753

Howard

[Jlawles2]

Bob, I bet if you take that chart, re type it so you can hide all of the NO stuff, you will see a clear picture of what is needed.

I see 5 colors that you are dealing with:
Gray = fan low
Green = fan high
Yellow = AC Compressor
White = Gas furnace
Black/White = heat pump

Drop the last function of heat pump and gas heat at the same time. instead set it up so that if outside temps are below 36F it defaults to gas heat and any time you call for gas heat trip the low fan.

[Reacher]

It's my understanding that heat pumps have an efficiency "sweet spot" between 50F-65F. They are operational down to 32F but are not as efficient as gas or electric below 50F for space heating purposes.