Honeywell THM5320R - Power

[idevcoop]

I'm attempting to replace a battery powered thermostat with the Honeywell unit.

I currently have four wires going to the battery powered unit; White, Red, Yellow, and Green. The battery unit has a jumper between two terminals labeled RH and RC and the Red wire is connected to one of these two terminals. The remaining wires map to terminals with letters specific to the wire colors (White to White, Yellow to Yellow, Green to Green) and it works well (the thermostat is in a bad location, hence why I'm trying to replace it with a wireless model). There is an approximate 28 VAC reading between the White and Red wires.

The question then is how to map this four wire combo to the Honeywell?

I thought that the White to Common/Power, the Red to Red/Power, the Green to Green and the Yellow to Yellow would do the trick, but no luck (jumpers exist already to RC and RH and Red). I have tried the White to White as listed in the documentation, but again, that's not powering the unit.

What am I missing, what can I try?

Thank you greatly for your suggestions!

[Mr Bill]

idevcoop -
There is an approximate 28 VAC reading between the White and Red wires.
>
> The question then is how to map this four wire combo to the Honeywell?


If your getting a reading of 24/28 volts at the stat you must already have a common run. The red wire that normally runs to the stat is just one side of the transformer, the common from the transformer makes up the other side that "normally" goes directly to the other sides of any "coils" or controls in the system. When you turn a stat on, all it does is feed the power from the red wire, through the Green,White, or Yellow to whatever they control. Normally the Green controls fan, the White heat, and the yellow the outdoor condenser. You said there is an approximate 28 VAC reading between the White and Red wires, well to me this means the white must be a common.

[Mr Bill]

theduke03 -
> I disagree. That volt reading is the open cicuit between R and W.


It's ok to disagree, go pull your stat and measure between the R and W and see if you get any voltage, that will answer it for sure, right?

[Mr Bill]

** theduke03 -
> Wrong. By that logic then any other wire would be common since you would
> read 24v between R and W,Y,G, and C if connected.*/*

** theduke03 -
> I disagree. That volt reading is the open cicuit between R and W. */*

Duke, you said there will be a voltage reading in the open circuit between the R and W, have you measured that yet?

[Freon]

Since you had a battery powered thermostat, I will assume the white wire was used for the heating circuit. But you need to always verify that the color of any given colored wire is connected to the same designated terminal (R, W, G etc) at both the thermostat and control board at the furnace. In your case, to have all the same functions (heat, fan, cold) you will need a 5th wire to bring the common terminal at the furnace control board to the common (C) terminal at the thermostat for its power.

As for measuring voltages between the transformer hot (R) side and other connections, depending on what safety switches are present and their normal open/closed state, you may or may not see a voltage differential. It is true that all the other terminals (W, G, Y and C) eventually connect to ground, known also as the common and being the other side of the transformer secondary. However they connect through a series of devices including semiconductors and coils and switches. All these devices have impedance and therefore will cause a voltage drop, assuming some safety switch isn't normally open in which case you'll see no voltage drop... it will look like an open circuit, since it is until the switch closes.

[Mr Bill]

Yep! some folks are long on mouth and short on ears. A little nonsense now and then is cherished by the wisest men.

[heatseeker]

Mr. bill is way off freon is way on.As for the op call the service company nearest you because you are going to fry something. Wireless t-stats require a little knowledge of electrical theory.

[Mr Bill]

heatseeker -
> Mr. bill is way off freon is way on.As for the op call the service company
> nearest you because you are going to fry something. Wireless t-stats
> require a little knowledge of electrical theory.


I just saw this! The "real" Mr. Bill had nothing to do with this, it would be his 17 year old "still learning son" that contributed to this thread. The "real" Mr. Bill has been doing this since 1978 and he knows exactly how this wiring works, and your right "freon" nailed it. This is what happens when "firefox" saves our passwords, I will have to correct that.

[heatseeker]

good, let the flogging begin.

[Mr Bill]

heatseeker -
> good, let the flogging begin.


Naw, just a good tongue lashing worked.