How to test a wall thermostat to see if it's actually working?

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It finally got cold enough at the house to turn on the heat, for the first time since last winter - and - and - nothing happened.
The heat didn't go on all night, so this is what I saw in the morning:
http://farm8.staticflickr.com/7419/11310109494_532b188768_o.gif
I really do not understand how home heating systems work.
I figured I'd start by taking apart the thermostat to see if I can test if it's giving the right signal to it's Payne 394JAW propane heater:
http://farm3.staticflickr.com/2890/11310161773_92c9c93247_o.gif
The little mercury bulb appears to work, at least at the extremes:
http://farm3.staticflickr.com/2837/11310034795_e5d6aa35f3_o.gif
And, there's this calibration thingy that seems to be already set:
http://farm4.staticflickr.com/3796/11310082936_811339eb39_o.gif
But, I couldn't see what I'm supposed to *test* without removing screws:
http://farm8.staticflickr.com/7452/11310034295_87ff18c35f_o.gif
Yet, once I removed the three flathead screws, I was met with this!
http://farm4.staticflickr.com/3797/11310108194_e1d18b3e08_o.gif
May I ask: Q: How do I test this thermostat to see if it's actually working?
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On Tuesday, December 10, 2013 11:54:27 AM UTC-5, Danny D'Amico wrote:

The photos appear to show a heating only thermostat, a very basic one. For heating with one stage, which is all that tstat is capable of, you would have 3 wires: power, heat, fan. While there is no standard that must be followed, typically red is the power, white is heat, green is fan. That leaves the blue. What it's doing there, IDK. If you had AC, I'd say it goes to that.
But, in any case, connecting red to white should fire the furnace. And connecting red to green should turn the blower on. Given the simplicity of the tstat, I would suspect it's not the problem.
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The switch in the left side is for cool-off-heat. The blue wire is connected to the Y terminal for cooling.
Yes, it is a very simple system...
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On 12/10/2013 12:16 PM, snipped-for-privacy@optonline.net wrote:

Blue is often the common, or the other side of the transfomer.
I didn't look at Danny's pictures. Simple test for Tstat is to remove it from the wall. Crank it cold, and see if there is continutity between R adn W (should not be). Hot, should be.
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On Tue, 10 Dec 2013 09:16:34 -0800, snipped-for-privacy@optonline.net wrote:

My fault...
I should have mentioned that the thermostat also controls the A/C. Here is a picture showing the "COOL" setting:
http://farm8.staticflickr.com/7343/11310819145_0d33aae09d_o.gif
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On Tuesday, December 10, 2013 12:40:35 PM UTC-5, Danny D'Amico wrote:

Then I agree with Rick, blue should be for cooling. I saw something on the left, but I didn't see anything labeled for cooling vs heating on the thermostat housing and whatever was sticking out, looked very small. Almost like it was cut off.
So, hook red to white and the furnace should fire up.
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Danny D'Amico wrote:

Hi, Don't blame 'stat. Have a look at furnace to see if it ignites when signal is sent from the 'stat. Don't touch that anticipater it is preset for the furnace. Has nothing to do with problem. Most likely your problem is in the furnace. What kinda preventative maintenance did you do during off season?
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On Tue, 10 Dec 2013 10:57:28 -0700, Tony Hwang wrote:

Preventive maintenance?
ummm.... < embarrassed look > ... er .... ummm... ah ... well I ... er ... I um ... ... well ... I didn't do any.
Given that ...
What *should* I have done in the off season anyway?
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On 12/10/2013 12:40 PM, Danny D'Amico wrote:

Typically, yellow for cooling. But, if the blue is connected to Y at the air handler, we're all good.
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On Tue, 10 Dec 2013 13:02:31 -0500, Stormin Mormon wrote:

Based on this discussion of colors and abbreviations, I took a closer look and snapped this large-format picture for you to guide me:
http://farm8.staticflickr.com/7395/11312016114_3f61f28c11_o.gif
As you guys noted, there seem to be 6 labelled attachment points, with the following 4 wires connected:
R = red wire W = white wire G = green wire Y = blue wire B = nothing is attached O = nothing is attached
Is the voltage to be expected a DC or AC voltage? What's the range? (I'm assuming it's *not* 120VAC!)
What would you use as the ground point for the voltage test?
PS: I will jump the wires, as suggested, but first I want to see what we have before I jump stuff.
PS: I don't see a fuse, but I do see a resistor.
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On 12/10/2013 2:06 PM, Danny D'Amico wrote:

SM: Should be 24 VAC. May be as high as 28 VAC, but that's rare.

SM: As with our discussion of lamp timers, this thermostat appears to only be connected to the "hot" side of the transformer. No common is found at the stat. with a modern VOM, you can read through a load.

CY: That sounds very wise. I'd read R to W, and see what kind of AC volts you get.

SM: If there is a fuse, it's inside the furnace. And, yes, there is very likely to be a fuse on the circuit board. Probably blade fuse, 3 amps.
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On Tue, 10 Dec 2013 16:42:11 -0500, Stormin Mormon wrote:

I got 27 VAC at a whole bunch of those connections.
The problem was I wasn't sure which *two* points to choose in order to test and debug why the heat wouldn't go on.
For example, I test VAC from the RED wire to what? I test VAC from the WHITE wire to what? etc.
Is there a ground on this thing?
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On 12/10/2013 5:36 PM, Danny D'Amico wrote:

The stat you describe does not have a ground, or a neutral. It switches the hot wire only.
I strongly sense the problem is not the stat. Your problem is in the furnace itself.
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On Tue, 10 Dec 2013 18:05:23 -0500, Stormin Mormon wrote:

Hmmm.... OK. I guess. I'm not used to having a hot wire and no ground though, simply because you need *two* points to test a voltage.

Everyone else said the same thing, so, I've actually buttoned up the thermostat, and moved on to the furnace itself.
Besides, someone said I can jump whatever needs to be jumped from down there anyway. Right?
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On 12/10/2013 7:00 PM, Danny D'Amico wrote:

Oh, heck. The most expensive appliance in your house, and you're crossing wires cause "someone" said?
I think common sense is lacking, here.
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On Tue, 10 Dec 2013 23:02:31 -0500, Stormin Mormon wrote:

I haven't actually "jumped" any wires yet, mainly for that reason (that I don't know what I'm doing yet).
I *did* read the entire PDF sent to me by the Carrier company, which explained how the system works by connecting "red" 24VAC power to Red to "call for heating".
It was interesting that the fan (green wire) is actually controlled by the furnace fan-control PCB board. Apparently the green on the thermostat merely sets whether the fan is always on or whether it's controlled by the furnace PCB board.
And, it was interesting that the fan speed is typically set to low for heating and to high for air conditioning.
I also learned the size of my system is "036065", which means it's 80,000 BTU/hour for heating and 1220CFM for cooling.
Is that a pretty normal home heating and cooling system?
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On 12/10/2013 11:24 PM, Danny D'Amico wrote:

Normal is based on the size of the house, climate, windows, insullation, occupancy, how often the doors are opened, trees, sunshine, price of fuel, and a couple other things. Normal isn't the same for everyone.
Yep, connect red to red, to call for heating. Sigh. (shakes head)
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On Wed, 11 Dec 2013 08:03:44 -0500, Stormin Mormon wrote:

Mea culpa. That was (just) a typo. I had corrected it a few minutes after I had posted (but you responded to the original). Sorry. That was my mistake.
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On 12/11/2013 10:13 AM, Danny D'Amico wrote:

Very well, my son. Please recite ten Book of Mormons, twenty Angel Moronis, and go and sin no more.
Hope you get your heat running, safely, soon.
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On Wednesday, December 11, 2013 12:26:46 PM UTC-5, Stormin Mormon wrote:

More likely there will be a pile of disasembled parts all over the place. He seems to prefer that to focusing on the obvious. So, the furnace doesn't fire up. Who starts by taking apart the tstat, asking 100 questions about how to debug it, without going to look at the furnace and seeing that the blower door is off, that he took off a few months ago? Good grief.
I have to give him credit for the longest threads, the most pics, etc. IMO, he should just call a tech.
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