Programmable Thermostat

[Douger]

I decided to replace my 6 year old digital thermostat (Honeywell), with a new programmable thermostat (Hunter).

The wiring is the basic White,Yellow, Green, Red.

The new thermostat had the following connections:

G - RC - RH - Y/0 - W/B - Y1 (A jumper wire between RC & RH came pre-installed).

I connected the wiring & ran the a/c, it worked fine. I kicked on the heat, it ran fine & cycled off but, the flue purge motor continued running after the furnace had shut off. (It never did this with the old thermostat.). I had to shut off the motor with the rocker switch on front of the furnace. I double checked all connections & they were secure & correct. I double checked that the switches on the back of the thermostat were set to "STD" as opposed to "HP" & "HG" as opposed to "HE". I ran the furnace, same thing, purge motor kept running.

I did some poking around on the net & came across several websites that said to disconnect G, & if the motor continued to run, the problem was most likely a stuck relay. I had an electrician look it over & he said he didn't think it was a stuck relay & he suggested to re-connect the old Honeywell thermostat & see if the motor continued to run. It didn't.

I assumed I had a bad thermostat. I returned the Hunter & purchased a Honeywell. I connected the new Honeywell, fired up the a/c, everything worked fine. A few minutes later, I fired up the furnace, let it run, cycle down & shut off...the purge motor continued to run.

Obviously, it wasn't the thermostat. I re-connected the old Honeywell, fired up the furnace, let it run, cycle down & shut off, the purge motor also shut off.

Can anyone shed some light on this. I'm not the most mechanical person but, something that should be simple has me stumped.

[Tony Hwang]

Hi, No trouble code from your furnace control board by way of blinking LED?

[Douger]

No sir.

[Tony Hwang]

[Douger]

I guess it's called the inducer motor, I'm not sure; it isn't the blower fan/motor though.

What I don't understand is, why the inducer motor shuts off, like it's supposed to, with the old thermostat. Seems to me if it was a logic board or whatever, the problem would be present no matter which thermostat was connected.

I'll try your suggestion & see what happens.

[dss]

Douger,

Since it runs fine with the old thermostat, the problem has to be in the new one. That's the only thing you've changed.

I recently switched to a six-wire, dual fuel (heat pump and gas forced air) system from a standard three-wire one. The thermostat has a "set- up" mode that controls a multitude of things (40+) as the system is rather complicated. It is accessed by pressing a certain combination of "buttons" on the display and then quickly gets rather cryptic (ie code numbers and values). But, that should be covered in the manual and I doubt you would miss it.

The other possibility is that you are getting the wrong kind of thermostat (hence the six connections). Years ago when I did the same thing I bought a programmable one that only had three connections. However, I didn't have a purge motor as it was an 80% job. Maybe my new system has one, as it is 96% efficient and I just don't realize it.

Good luck.

dss

[Douger]

Yes, I came to the same conclusion.

I've had the old Honeywell connected & it works fine, save for the sticky "down" button; which is why I needed to replace it to begin with. It's stuck @ 71 degrees.

I guess I'll look for a thermostat with just the G - R - W - Y wires but, it's hard to see the connections without opening the package.

[dss]

Douger,

If you get one that says it doesn't work with heat pumps or multi- stage furnaces it should just need the three wires. They are also usually cheaper. If you have a multi-stage you may be hosed.

I'll probably be doing the same thing for my daughter when she buys a new house, so let us know how it turns out.

dss

[Douger]

I'm not following you. Are you saying I only need to connect 3 of the wires?

[trader4]

Typically you have 4 wires:

hot wire, ie current source heat on A/C on fan on/off, ie so you can have the blower run all the time or only when heat or AC makes it go on.

Your problem is very strange, because per above, nothing from the thermostat should have an effect on the inducer fan. That is controlled by the furnace contoller/logic board. The thermostat justs connects the hot wire to the heat wire to tell the furnace to fire up. From there, the furnace controller starts the inducer, turns on the gas, ignites it, starts the blower, etc. When the thermostat opens, the furnace starts the shutdown sequence.

How long have you let it just sit there with the inducer running after the furnace shuts off? Does it just keep running indefinitely?

The only thing I can possibly think of is I think some thermostats steal small amounts of power from the circuit to keep batteries charged. I don't think most of them do that, but believe some do. It could be that having that small current flow even when the heat circuit is essentially open is somehow disrupting the controller in the furnace. But that seems a long shot.

Might be time to get a HVAC pro.

[dss]

Douger,

Forget my mention of three wires. I'm probably not remembering correctly as it was 20 years ago when I installed the programmable thermostat. The old one was one of the round analog models.

At the big box stores they have thermostats that work with heat pumps and multi-stage furnaces, and those that don't. It's usually noted on the back of the package in small print. I think you need the one that can't control a heat pump. The simpler one should not have six connections on the back. Although, from your first post it sounds like you can get around that by setting some switches.

It's probably time to ask the people at Honeywell what thermostat you should use to replace your existing model. The old one is either doing something or not doing something that your replacements are not replicating.

Good luck. Something this simple shouldn't be so difficult.

dss

[Douger]

Typically you have 4 wires:

hot wire, ie current source heat on A/C on fan on/off, ie so you can have the blower run all the time or only when heat or AC makes it go on.

Your problem is very strange, because per above, nothing from the thermostat should have an effect on the inducer fan. That is controlled by the furnace contoller/logic board. The thermostat justs connects the hot wire to the heat wire to tell the furnace to fire up. From there, the furnace controller starts the inducer, turns on the gas, ignites it, starts the blower, etc. When the thermostat opens, the furnace starts the shutdown sequence.

How long have you let it just sit there with the inducer running after the furnace shuts off?

Well, I'm not sure. When I initially tested the heat setting with the new thermostat, I didn't notice the inducer running on until, oh, maybe 5 minutes after the heat shut off. I waited maybe another 5 minutes for the inducer to shut off on it's own before I manually shut it down with the rocker switch on front of the furnace.

Does it just keep running indefinitely?

Not sure. I know with the old thermostat the inducer would shut down at the same time the fan blower shut down (or maybe just before the fan shut down), either way, the inducer never ran on after the furnace shut down with the old thermostat connected.

The only thing I can possibly think of is I think some thermostats steal small amounts of power from the circuit to keep batteries charged. I don't think most of them do that, but believe some do. It could be that having that small current flow even when the heat circuit is essentially open is somehow disrupting the controller in the furnace. But that seems a long shot.

Might be time to get a HVAC pro.

I think you may be right.

I just don't like the idea of getting jacked to the tune of $75 for a service call & $50/HR. , for what I **know** will be a simple fix. (well, simple for the HVAC guy anyway).

[Douger]

According to their manuals, both the Hunter & the Honeywell are for "Heat/Cool only & are not compatible with heat pumps or multi-stage systems."

I'll check into that.

TY...you're right, it shouldn't be difficult but, everything I attempt to fix myself turns into a monumental task; so y=this comes as no surprise to me.

[The Daring Dufas]

I sell digital thermostats that can use either/or batteries and 24 volts AC from the air handler. The standard color code for wires for the thermostats will give you 24 volt power for the 'stat from the red and blue wires from the air handler/furnace. I leave the batteries in them so no presets are lost in case of a power outage. An advantage of 24 volt power is a continuously lighted display can be programed. It's a good thing to have in a dark hallway at night. The simplest hookup for a furnace powered digital 'stat uses 5 wires: red, white, yellow, green and blue.

red - white = heat

red - green = fan only

red - yellow = AC

red + blue = 24 volts ac power

TDD

[Douger]

What's the old saying?.."Timing is everything."

As I mentioned in an earlier post, I would re-connect the new Honeywell & see how long the inducer motor ran after the furnace shut down. The red wire slipped back into the wall, as I was pulling it out, what do I see?...a BLUE wire! Obviously this wire has never been used, as the insulation is still intact. Per your post above, I need to connect the blue wire? To which terminal?

This is how the new thermostat wires up now:

Y - Y G - G W - W/B R - Rh

I hope this blue wire solves this problem.

[The Daring Dufas]

The red wire should be considered like the "hot" wire on your house wiring. The blue wire is akin to the "neutral" on your house wiring and the blue wire is often attached to the chassis of the air handler or furnace. If the thermostat has a "C" terminal, this is the common terminal and where the blue wire should be connected. If you hook the blue and white wires together on the thermostat, the transformer fuse or transformer will burn out when the thermostat is switched to heat. Your best bet is to carefully read the directions that came with your new thermostat. One very big problem is that there are common wiring schemes for most thermostats but certain manufacturers don't always follow them. It's best to compare the wiring diagrams of the furnace and thermostat for a proper connection. Heat pump wiring can be a whole different can of worms and care should be taken when wiring the controls. Here's a link that shows the most common wiring scheme.

TDD