Thermostat Confusion

[Micscience]

I understand the basics of what the color coded wires are for. My furnace doesn't have any colored wires connected to its control unit besides the red and white wires. The other colored wires do not attach to the control unit of my furnace. Though my thermostat has the two red and white wires, and the color coded wires attached to it. I followed the b,y,o,g wires and it lead to an adapter that you plug in basically a (wall wart). I am assuming this is some sort of transformer since it has two screws attached to it on the back side where the colored wires attach. The funny thing here is this device wasn't plugged in but my furnace has been operating fine. So my question is I guess, all you need is a power and return line?

 

[gmcgeo]

The terminals are usually marked ‘R’ and ‘W’. They usually operate at 24V ac power, and the source of this control power comes from a control transformer mounted either just outside, or inside the furnace body. The line voltage feeding the furnace "to operate the fan blower motor" is transformed down to a safer level of 24 volts "the gas control valve needs 24 volts to open", and after making a series loop through at least one safety device (the most basic and mandatory one is an over-temperature shut down), the power goes up to the thermostat, and when the room temperature falls below the set-point, the contacts close completing the circuit to the gas valve allowing it to open, the main burner to ignite, and begin the heating cycle.

If your home’s system of this vintage has provisions for air-conditioning (cooling), then the thermostat wiring will have at least three wires (some will require a separate ‘R’ terminal for heating and cooling and will be labeled ‘Rh’ and ‘Rc’ now needing a minimum of 4 wires), ‘R’, ‘W’, and a ‘Y’ terminal.

When the mode is selected for cooling (basic heat / cool thermostats have a mode selector for either ‘heat’, ‘cool’, or ‘auto’) when the room temperature rises above the set-point, the thermostat will close the connection between the ‘R’ and the ‘Y’ terminals completing the circuit to the compressor and condenser unit that provides the cooling for the evaporator coils mounted in the discharge ducting of the system.

This is good info here also for in depth on Wiring for thermostats. https://learnmetrics.com/thermostat-wiring/

 

[Bert_]

For heat you only need two wires, R & W typically. With a digital stat now you either need batteries or a common wire, a C wire. If you have AC that adds another wire for the condensing unit, that's Y. If you want to be able to run the fan manually then you run a wire to the G terminal.

 

[Micscience]

Ok I see I guess it has been running off the batteries for power. I only have heat though my furnace is cooling capable, it only does heat. What bothers me though is that freaking plug. Why are there colored wires attached to it? Has anyone seen an external power source such as a plug in for a furnace?

 

[Micscience]

Anyway I have heat now. I went a full day without heat during the coldest part of the season. It makes you appreciate the things we modern people enjoy. I guess a 3 amp fuse blew and I replaced it and everything is up and running now. Thanks guys.

 

[PoorUB]

There is about a million different htermostats. We could help you better understand your system if you posted some model numbers.

 

[fitter30]

What letter is by each wire? If theres a Rh and Rc most are jumped together with just one wire.