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

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:

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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:

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The little mercury bulb appears to work, at least at the extremes:

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And, there's this calibration thingy that seems to be already set:

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But, I couldn't see what I'm supposed to *test* without removing screws:

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Yet, once I removed the three flathead screws, I was met with this!

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May I ask: Q: How do I test this thermostat to see if it's actually working?

Reply to
Danny D'Amico
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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.

Reply to
trader4

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...

Reply to
Rick

My fault...

I should have mentioned that the thermostat also controls the A/C. Here is a picture showing the "COOL" setting:

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Reply to
Danny D'Amico

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.

Reply to
trader4

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?

Reply to
Tony Hwang

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.

Reply to
Stormin Mormon

Typically, yellow for cooling. But, if the blue is connected to Y at the air handler, we're all good.

Reply to
Stormin Mormon

Danny,

You're testing the wrong things. The thermostat is very unlikely to fail. Please put the thermostat back together. Now slide the fan button to "on". Does the fan come on? This will tell you whether there is electricity going to the furnace (?). What sort of heater are we talking about?

Dave M.

Reply to
David L. Martel

Based on this discussion of colors and abbreviations, I took a closer look and snapped this large-format picture for you to guide me:

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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.

Reply to
Danny D'Amico

I don't know anything about heating systems; so, I was planning on debugging from the thermostat to the furnace.

The furnace is a Payne 394JAW, built in 1988.

I called Carrier this morning (800-227-7437x4) and asked for a troubleshooting guide and parts list. They said I had to go to a local dealer, but, they did send me a document named: 40394dp65-a.pdf, and titled: Bryant, day night, Payne 394J, Series B, Sizes 030 thru 095, 40394DP6-A 10/15/87 installation, operation, and maintenance instructions Upflow Gas-Fired, Natural-Draft Furnace, 9 pages For use in California only Cancels 40394DP61-A

BTW, where can I post this PDF so you (and others) can see it, as I couldn't find anything on the web for how to troubleshoot the furnace itself, and the four companies that Carrier told me to call all told me to take a hike (in effect). They don't deal with residential consumers, at least not for PDFs and parts orders.

NOTE: I'll see if I can convert the PDF to JPG so I can post it for you...

Reply to
Danny D'Amico

Just upload it here and you will get a URL you can post in a text message.

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Reply to
Metspitzer

OK. Here is the 9-page Payne 394 JAW PDF that Carrier sent me today:

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I had also just finished converting it to PNG for upload to Flickr: P1:

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P2:
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P3:
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P4:
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P5:
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P6:
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P7:
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P8:
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P9:
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I'll head on down to the furnace after checking the thermostat; but, I'm tending to agree with you, that the thermostat looks too simple to be the problem...

Reply to
Danny D'Amico

*Based on past experiences with customers, two things I suggest that you check. Make sure that the disconnect switch for the furnace is on, and make sure that the service door on the furnace is closed correctly. If the service door is not closed properly the furnace will not run.
Reply to
John Grabowski

Your furnace will have terminals marked on the boards; C, W, G, Y(if AC is present. C is common lead for control power, 24V AC), W is heat lead, G is fan lead, Y is compressor lead. If you jumper C and W heat with come on and after some delay fan will start. If you jumper C and G fan will run. Make ssure the furnace cover interlock switch is cheated with a piece of tape.(this switch breaks power to the furnace when open)

You can do this jumper test from thermostat terminals too. Do you have multi meter? Know how to it and read schematics? Fiurnace is just simple one line logic sequence......

Reply to
Tony Hwang

I was hoping to just debug the (much simpler?) thermostat first, but, since someone asked about the furnace, I went down there and noticed the door was off.

When I put the door back, the blower just blew incessantly.

So I took the door back off, and pressed the white switch that gets pressed when the blower door is on, and the blower just kept blowing for as long as I held the switch pushed in.

Back upstairs, teh cover is still off the thermostat, so the thermostat settings are still at HEAT (versus OFF, COOL) and AUTO (versus FAN ON).

This is the schematic printed on the inside of the door panel:

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This is another smaller schematic above that big one on the door panel:

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And, this is on the outside of the door, for the electric pilot:

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What I'll do right now is read up on the net for how this furnace works, and the first thing I'll do is try to identify the parts.

Reply to
Danny D'Amico

Hi, Close the cover. And shut the power off to the furnace for 5 mins or so and turn on the power. What happens now? Still fan comes on? Then we'll do next step. Usually when hi temp limit switch(fixed temp. thermostat) triggers furnace flame shuts off and fan runs to cool and when that switch opens, fan will stop. I don't think your furnace is hot now. Just maybe thatr switch is stuck close.(this is just one of possible scenarios)

If this is the case furnace will lock up 2 hours something like that. By turning power on/off you can defeat that 2 hour wait to try again. Is it cold there? It is -14C and light snow here today.

Reply to
Tony Hwang

Danny,

I went down there and noticed

How did that happen? Who left your furnace open and why?

Ok, you've got electricity to the furnace. No blown fuses etc.

At this point the fan should not be on.

Read section IV of the manual. It explains what should occur and when in the heating process. Confirm that you have gas. Find the furnace switch in your breaker box. Turn it off. Give it a few minutes. Turn it back on

Dave M.

Reply to
David L. Martel

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.

Reply to
Stormin Mormon

So, page eight or nine had trouble shooting. I hope Danny did those checks.

I tried download the PDF, but the file came through corrupted. What I was able to see of the PNG, there is very little troubleshooting information provided. And precious little about the furnace.

Reply to
Stormin Mormon

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