Thermocouple

[jcwvam]

Just tested the thermocouple on a
Robert Shaw 7000 series gas valve.
As described here, we got 27--30 mV
from the thermocouple tip when
heated with the pilot flame but when
screwed to the gas valve, the
thermocouple tip presses onto the
end of two heavy gauge wires that
seem to go up to some other point
in the wall furnace.
What is the purpose of those two wires?
Without them the pilot stayed lit
and gas valve seemed to
function correctly.
It seems difficult to understand a
circuit when the tips of the two wires are
pressed together by the end of the
thermocouple.
Is this a safety feature or a
necessary part of the operation?
Thanks

[jdenyer]

Oh my god:eek:

[smokin68]

I highly recommend you step away from the furnace and have a pro look at it. Two people just lost there lives here in Fl. from co poisoning.....don't play with fire.

[mike3]

SAFETY--Yes Do not eliminate.

[Mr Bill]

Man, were are you were your concerned about heat this time of year it's 100 in Houston in the shade please invite me up I will fix it for free. :D

[billva]

you need a new gas valve.

shut off the gas supply immediatly to prevent danger to you and your family.

[rich pickering]

That's not a gas valve problem, it's a safety problem. You need somebody who knows what they are doing to look at it.

[rimek]

"Is this a safety feature or a
necessary part of the operation? "

wtf?

read that part again?
is this YOUR home?

Yes-the name is TCO- It is a safety device which interrupts the pilot circuit with a thermal cutout.


leave it 4 a pro-don't be a doofus.
If you knew what was going on, you wouldn't say:
"It seems difficult to understand a
circuit when the tips of the two wires are
pressed together by the end of the
thermocouple."

[beenthere]

Call a pro.

Need to find out why it tripped.

Don't bypass it.

[Jultzya]

Originally posted by billva
you need a new gas valve.

Really, I see a faulty limit due to improper flu piping/termination! :D

[jfs1138]

i think he's implying that there was in incorrect installation in the first place causing the thermocouple connection to short out. It could have functioned that way for a long time before the heat or pressure or something caused the insulation on those wires to fail shorting the thermocouple causing the valve to shut off in safety.

I'd say that you need to call someone to come out and fix the thing :) If you think it was installed in a way that crimps the wires from the thermocouple then call someone ELSE rather than the guy who installed it in the first place :D

Hard to get any specifics as to why it's unsafe with all the people scared to death that you're futzing with it, but without the thermocouple it can't tell if the pilot light has gone out and will flood your house with gas and it will blow up and kill you.

That would be bad, so do not defeat those connections and do not just leave it. Get it fixed asap. If it's going to take more than a few hours to get someone out there the advise to turn it off in the meantime is very good.

[Jultzya]

Originally posted by jfs1138
i think he's implying that there was in incorrect installation in the first place causing the thermocouple connection to short out.
No, I believe he has a problem and doesn't know how this system operated from the OEM.


It could have functioned that way for a long time before the heat or pressure or something caused the insulation on those wires to fail shorting the thermocouple causing the valve to shut off in safety.
Shorting the wires together is not going to cause this unit to fail the pilot valve!

Shorting then to the cabinet is a totally different animal.


Hard to get any specifics as to why it's unsafe with all the people scared to death that you're futzing with it
That's because WE are familiar with this set-up and the safety limit is most likely on the flu hood!


but without the thermocouple it can't tell if the pilot light has gone out and will flood your house with gas and it will blow up and kill you.
If he doesn't understand this simple idea... He has NO BUSINESS messing with it further!


That would be bad, so do not defeat those connections and do not just leave it. Get it fixed asap. If it's going to take more than a few hours to get someone out there the advise to turn it off in the meantime is very good.
Further, if the wires are connected (together) under the valve (beings the coupler was tightened to tight), this would not cause the pilot to go out!

This may sound HARSH, but this can be a very serious issue!

[jfs1138]

This may sound HARSH, but this can be a very serious issue!

No, you're right of course. perhaps it's just me, but when I ask a question I'd like more information than just yelling at me that i have no business asking the question.

Why wouldn't shorting the wires together cause the pilot to go out? That would stop the micro current from the thermocouple from getting to the sensor and it would think the pilot had gone out wouldn't it?

I can't really tell from his post if he's talking about the wires from the thermocouple or some other wires inside there. And I don't really think it matters. It's installed incorrectly or just busted if it doesn't work when tightened into position.

I think the classy thing to do would be to give him enough information so that he understands that he aught to call someone rather than just telling him he has no business touching it. If it were me that would make me angry and I'd want to try all the harder to do it myself. Whereas when I understand enough to know I'm out of my depth I'd be thinking, what a nice group of guys there on the internet to be concerned enough about me to explain why i needed some help on this project.

If he's the type of guy that will take that little bit of info that would show a normal person that they need help and try to do it anyway, then no amount of telling him to call someone else is going to work anyway. So you might as well give him the benefit of the doubt.

[jacob perkins]

Originally posted by jfs1138

This may sound HARSH, but this can be a very serious issue!

I can't really tell from his post if he's talking about the wires from the thermocouple or some other wires inside there.
I think the classy thing to do would be to give him enough information so that he understands that

I agree.
If I can get this sheet metal chip out of my eye,I might be able to read well enough to understand the question...

[Jultzya]

I'll post a diagram late tonight to show you why the wires being connected at the valve will not cause a pilot outage issue.

It will however, cause a safety issue!

[mike3]

The wires are not actually touching. There is separating and the wires go to a spill switch. At this point using a meter will tell you where to go. May need to take reads at multiple locations to pinpoint problem. This must be a "bulb t'stat" or or manual furnace to have a t'couple. Also is this one of the recall valves??

[Edited by mike3 on 06-24-2005 at 04:29 PM]

[jacob perkins]

Originally posted by jultzya
I'll post a diagram late tonight to show you why the wires being connected at the valve will not cause a pilot outage issue.

It will however, cause a safety issue!

Thank you.In the meantime,I will keep rubbing my eye and hope the irration goes away...

[Jultzya]

Here is the diagram I promised you...

http://www.imagewiz.net/usr/hvac1/11232_J-block_thermocouple_diagram_flow_2.JPG

The red current paths represent the limit being 'bypassed'!
(DO NOT DO THIS! This is for training ONLY!)

As you can see, it doesn't matter to the electricity flow whether the limit is in the circuit or not.

So if the 'ECOs plastic' gets damaged and the wires connect there, it bypasses the limit!

Does this clear up the whole 'thermocouple' wiring issue?

[Jultzya]

Originally posted by jultzya
Does this clear up the whole 'thermocouple' wiring issue?

Well, does this help anyone?

[jacob perkins]

Yes sir.
Sometimes I just post on these threads just because I want to come back and read the answers.Thats an easy way to remember.

In this case it was "wall furnaces" that got my attention.I dont see very many that arent condemned,and thrown on the junkpile.So,I wanted to absorb whatever knowledge I could here...

I must confess though,after putting half hour or more into this,I still dont really know what we are talking about...in other words, 2 minutes of actually seeing the unit would be much better.

However,the original poster probably has a better idea of what he is seeing,and that is what matters.

Thank you!