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

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On 12/11/2013 7:30 PM, Danny D'Amico wrote:

thing mixed in with the flame. Rust, maybe.
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Christopher A. Young
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On Wed, 11 Dec 2013 17:03:47 -0500, Stormin Mormon wrote:

It's interesting that you noticed that ... I will take a look to see what's going on. I personally don't have a clue as to why, or, if it is indicative of something ...
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On 12/11/2013 7:35 PM, Danny D'Amico wrote:

gas air mix into the burner box are tilted. And that burner 4, is full of rust.
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On Tue, 10 Dec 2013 19:43:29 +0000, Danny D'Amico wrote:

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:
http://farm3.staticflickr.com/2863/11313024713_51ef8ce342_o.gif
This is another smaller schematic above that big one on the door panel:
http://farm6.staticflickr.com/5518/11312983254_ab27d0a8ef_o.gif
And, this is on the outside of the door, for the electric pilot:
http://farm8.staticflickr.com/7374/11312899795_2d44b32818_o.gif
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.
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Danny D'Amico wrote:

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.
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On Tue, 10 Dec 2013 13:31:33 -0700, Tony Hwang wrote:

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 ...
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On Tue, 10 Dec 2013 13:31:33 -0700, Tony Hwang wrote:

Something I did must have worked, at least temporarily, because I got pilot light finally tonight:
http://farm3.staticflickr.com/2845/11318356605_a78bf71569_o.gif
And then I got main burner:
http://farm8.staticflickr.com/7397/11318411966_be80c6d243_o.gif
And then I got blower:
http://farm8.staticflickr.com/7427/11318411706_f7ceb36cd5_o.gif
But, I accidentally loosened the tape holding the door switch in, so the whole thing died.
Trying again and again, I was able to get it to restart a couple of times, but it shuts off almost immediately - like after just a minute or two - so I have to figure out what's turning it off ...
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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.
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On Tuesday, December 10, 2013 4:12:10 PM UTC-5, David L. Martel wrote:

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.

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On Tue, 10 Dec 2013 15:15:00 -0800, snipped-for-privacy@optonline.net wrote:

IIRC, I took it off months ago, when it was something like 95 degrees outside, but all I could do was stare at the setup as I didn't understand how to troubleshoot.
But, not having A/C in 95 degree weather is nothing like not having heat in 32 degree weather; so, it's more important to figure it out now than in the summer.
I'm ok, by the way; but the wife and kids don't like the cold.
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On 12/10/2013 02:21 PM, Danny D'Amico wrote:

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.
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On Tue, 10 Dec 2013 18:10:46 -0600, philo wrote:

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 ...
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Danny D'Amico wrote:

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.
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On 12/10/2013 06:38 PM, Danny D'Amico wrote:

Start with the basics:
1) You have determined that the furnace has power. That's good.
2) Turn the thermostat down below the temperature of the house... Have an assistant stand by the thermostat and now go to the furnace. When you are there have them turn the thermostat up.
Does anything at all happen?
Of so...describe what it is doing and post back.
If *absolutely* nothing happens, then a wire on the thermostat could be broken.
If you hear a click and gas starts to flow, but nothing ignites, then it shuts down...then the igniter is bad.
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philo wrote:

Then there is no reason blower would run. Just jumper W and C at the furnace after taping down the cover interlock switch. If furnace works go to 'stat and do the ssame. If furnace does not start then can assue wire is broken or loose some where.
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He already determined that the blower came on. Now, we need to determine why. That is why I asked for him to get the t-stat set up to all off, then have the cover replaced. If the blower turns back on something is making an improper contact, one of the relays is stuck, or the HTR relay is not functional (bad coil). That is if he is correct when he stated that he had a nominal control voltage. 27vac, I believe.
Be careful asking him to play with the access door switch. That switch has 120V going to it. Sometimes they are not finger proof. :-)
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Irreverent Maximus wrote:

I already mentioned about that too. Maybe he can read but can't comprehend? Getting zapped will make him call for pro help. It is hard to get killed by 120V AC unless one's feet are bare and wet. If he is afraid, some one has to be nearby to watch, ready to throw the breaker in case he is getting zapped. Desire to learn is good thing but one has to have some basic knowledge first. He can enroll at community college to take electricity 101 or some thing like that. Oh, no, then he'll be more dangerous knowing little bit......
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On Tue, 10 Dec 2013 18:18:16 -0700, Tony Hwang wrote:

I'm confused as most people said to jumper R & W, not W & C. Plus, there are two W wires!
http://farm8.staticflickr.com/7443/11315520763_a1bf7cb9e1_o.gif
Which W would you suggest I jumper to C?
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Check for 24VAC between SEC1 and SEC 2. If there is no 24VAC, check the transformer solder joints on the circuit board
Leave one lead on SEC2 and check for 24VAC on the red wire terminal. If you have 24VAC the interlocks are OK. If not, trace back until the open interlock is found
With the stat calling for heat, check for 24VAC at the W terminal. If you have 24VAC, the stat heat circuit is good. You should hear the gas valve click and the igniter spark.
If you look at the schematic for 394JA you will see the blower motor relay is normally closed. If the furnace is powered up and there is not 24VAC at the R terminal, the blower motor will run right away and not shut off, which is what you said it's doing (note the jumper between R and GH)
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Continue to trace the 24VAC as needed through the ignition lock out module and safety pilot to find the faulty part
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