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

I googled for the name of the document that Carrier sent me: 40394dp65-a.pdf

This directory came up; which contains a *lot* of furnace PDFs:

This one looks to be similar (it's for the 394J where mine is 394JAW):

This one has an even closer model number (394JAZ where mine is 394JAW):

Yep, not likely to be anything wrong with the thermostat.

May be a s simple is the furnace switch is turned off.

It could also be the ignitor if the furnace starts to energize but goes no further.

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.

I looked at the flicker ping pages, and there's not much useful information to be had. There was some troubleshooting, which I hope you read and tried.

Writtenly lookingish set not appearingly to be Chingrisher.

Turn furnace switch off. Connect the red wire to the white wire. Turn the furnace switch back on. If the furnace doesn't fire up, it's not the thermostat. It's unlikely it's the thermostat to begin with, so why waste time on all kinds of tests when there is a simple and very direct method?

I think that Danny was an engineer in an earlier life. He's really a wonderful fellow, and I truly enjoy his posts to this list.

That's a good question. Did it come off at some point in the diagnostic process or was it off to begin with and the cause of the whole problem?

The fan is probably on because he's been screwing around with the thermostat and now has something screwed up there.

With a simple old mercury thermostat like that, there isn't much to fail. I've never seen one that just stopped working.

Ignitor?

I need a quick lesson on the parts of a furnace ... and what they do, before I can diagnose or fix anything! :(

At first, I thought "this" was what you call the "igniter":

But, this youtube video calls that a "3-wire pilot assembly":

Following the red "high tension lead", that video calls this black box the "spark igniter" (is what you meant?):

This is clearly what that video calls the "gas valve":

This isn't in the video, but, it's clearly some sort of fusible link and something called a "lockout timer":

The brown board with the fusible link attached has two wires that go upward to this thing (is it a sensor?), which, unfortunately, wasn't described in the video:

This compartment was held shut with a 1/4" sheet-metal screw:

Below that compartment was this set of terminals (I recognize those wire colors as the same as those of the thermostat):

To the right of the terminals, this 3Amp fuse tested good:

Inside the box was what the video named a "fan control board":

And, I observed the basic stuff, such as this door safety switch (which I taped tightly to keep in the on position):

This is the on/off switch for the gas, which remains on:

The 16x25x1 3M filter was surprisingly clean:

Googling, I found there usually is an on/off switch on the side of the furnace where the power comes in. Mine doesn't seem to have that switch; the power wires go right inside the furnace from outside without a switch.

So now that I've identified "most" of the parts (I'm not sure what the purpose of the lockout timer and that sensor thing are), it's time for me to figure out what/how to test and debug the thing...

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

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?

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?

If the blower is working that means the furnace is getting power.

That's as far as you should go.

Unless you know /exactly/ what you are doing, a furnace is one thing you should not fool with.

Thanks. I just printed that manual and haven't tried that troubleshooting yet. It took all this time to learn how to identify what was there, and I think, for the most part, I've figured out what most of the things do.

I'm not yet sure what this thing is (a sensor?):

Nor, am I sure why this thing called a Lockout Timer exists:

So, I'm taking in the data, bit by bit and will get to the troubleshooting guide from Carrier.

2nd: Put thermostat back together making sure that all switches are in the -off- position, and turn the temperature select to its lowest setting.

Does the blower immediately turn on still?

If no: Switch thermostat to -heat- and set to highest temperature. Go back to the furnace and listen. The blower should be running and in a minute, or so, the burner should kick on. This unit might have a delay for the blower, so wait 2 minutes before deciding that things are not functioning. That is it for this part until you come back with an answer.

If Yes: Either the heating or the cooling relay is sticking. Once again, get back with an answer.

Anyway, download above link. If it is corrupted, update your PDF reader.

There is no furnace switch, that I know of. The wires come directly into the furnace from the outside. Of course, I can shut off a breaker ...

OK. I have the breakers off. I'll wait a few minutes now.

From another post, before I ruin something, is this correct? a. Connecting red to white should fire the furnace b. Connecting red to green should turn the blower on

Is this where I should make those jumper connections?

BTW, normally I *measure* stuff (voltages usually) before jumping from one point to another; but I would need to know what *two* points to measure. Based on Stormin' Mormon's prior post, I'll read:

A. Red to White (AC voltage) ... is this what I should read? B. Red to Green (AC voltage) ... is this what I should read?

NOTE: I haven't finished reading everything, so, if I'm repeating, I apologize.

I've buttoned up the thermostat. It just took me a while to report back because I was trying to figure out how the darn furnace works and what the parts were...

I am in warm clothes, but it's going to be around freezing in Silicon Valley tonight, so, for *us*, that's coooold!

Yes, I know, that's warm for most of you!

Anyway, I'm reading all the suggestions, and lining up my ducks, as I am first and foremost trying to figure out how the darn thing is *supposed* to work.

So, for that, I had to first identify the parts, which, for the most part, I think I have now.

So, now it's time to try to figure out how the thing is supposed to work.

And then on to the debugging steps.

I'll report back, as it's getting dark and colder outside as I type ...

Dunno. But, I probably went down there. I think I remember, in the hot days of summer, it was up to about 95 or so here in the Silicon Valley, that the A/C didn't work.

So, I think, IIRC, I opened the door. Stared. Stared some more. Stared a bit more. And I must have left it with the door open.

Still don't know why the A/C didn't work - but that's long ago now, and it's time to figure out why the heat doesn't work.

I'm still catching up on all the reading, so, I apologize if I'm slow to get back to you on the troubleshooting ...

The fact that I assume 120 volts (and whatever the high-tension leads have in them) is there, is the key reason why I'm not just jumping leads just yet.

I want to *measure* first. That's not dangerous. Jumping things is much more dangerous (if I make a mistake).

So, at the moment, I concentrated first on identifying all the parts of the furnace (which I snapped a picture of and posted separately).

Then, I am concentrating on figuring out how those parts play together.

After that, I'll do the measuring.

And then the jumping.

I'm sorry I'm probably way slower than you guys would like, but, I'm trying to actually understand the darn thing first ... Thanks for your patience. I've still got to read that Carrier manual ...

Was the blower running at this time?

Hi, Jumping is involved with 24V AC control voltage. Not dangerous. Let me ask you, can you read schematics? Can you id. parts in the furnace like piezo ignitor, limit switches(some are NO, some are NC), do you understand relay logic? First thing I suggested you was to reset the furnace by powering it off/on. Gently tap all the relays you can see. Am\nother issue may be you may have messed up the 'stat when you open it and reassembled. We're going around same routine when you had alarm trouble wating lot of time.