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

[Rick]

That's the igniter...

[Rick]

Wonder if he's related to Stryped..... .

[The Daring Dufas]

Yep, that's a limit but look to see if there's a little push button reset between the 1/4" Faston terminals where the wires plug on to the switch. Some of them have a manual reset that will click when it is pushed in to reset it. ^_^

TDD

[Danny D'Amico]

Wow. I tried this just now, in the dark, and, for a short while, everything was working again!

The click click click I had heard was a snapping sound as the pilot was being lighted. Soon, the pilot light lit!

Then, after about a minute (I didn't measure it), the entire burner was aflame!

And, within another while (again, I didn't think to measure), the blower ran!

I accidentally hit the door switch while I was trying to measure voltages, so the whole thing shut down - and I couldn't reproduce the success - but - I'll try again tomorrow when I have more light to work with (and it will be warmer besides, as it's going to be at freezing tonight).

[Danny D'Amico]

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?

[Danny D'Amico]

Ah. That must be this thing:

The funny thing is that the PDF didn't say what caused the igniter to start snapping. I guess I'll read the PDF again ...

Ah ... found it... It must be the thing called the "pilot igniter".

Here's what the PDF says about it: "When the thermostat calls for heat, the control circuit is closed between the terminals R and W. Power from transformer TRAN through fusible link FL, limit switch LS, and vent safety shut-off switch VSSS, energizes the pilot valve part of automatic gas valve GV and *pilot igniter PI*. The pilot valve opens, permitting gas flow to the pilot burner where it is ignited.

So, I guess that snapping was from the "pilot igniter".

[Danny D'Amico]

It is. There are actually *two schematics* on that inside cover. I'm not sure how this lockout timer module works; but it might be the culprit:

Otherwise, this is the schematic:

[Danny D'Amico]

Here's my summary of the PDF, after reading it a couple of times:

1. Red wire is 24VAC hot.
2. Thermostat "calls for heat" by connecting Red to White.
3. Thermostat "calls for fan" by connecting Red to Green; but the fan is actually controlled by the fan PCB so the thermostat only tells the fan PCB if it's to run continuously or automatically.

Details: Thermostat "calls for heating" by connecting Red to White.

Power goes from the 24VAC Transformer -> Fusible Link -> Limit Switch -> Vent safety shut-off switch -> pilot ("pick" & "hold" gas valves) such that pilot gas flows.

Power also flows to the igniter, which ignites the pilot flame.

60 seconds after pilot, safety pilot switches its contacts and energizes the main valve portion of the gas valve, where, about 10 seconds later, the main gas valve opens, and the gas is ignited by the pilot flame. 75 seconds after pilot, the fan control board activates the fan on low speed.

When the thermostat "is satisfied", the connection between R & W is broken. Gas is immediately stopped to both the pilot and main burners. The blower continues for about 100 seconds.

If the furnace overheats, the Limit Switch opens.

If the furnace overheats in the vestibule, the Fusible Link opens. If the furnace overheats in the vents, the Vent Safety Switch opens. (I have not found this VSSS yet.) There is also apparently a Lockout Timer for the gas flow:

The PDF does not explain how that lockout timer works though ...

[John G]

Two things. The timer is there to set delays between various operatins and you will be very confused if you expect things to happen immediatly whenever the conditions change.

The Thermostat must always be mounted as though it was on the wall so that the mercury switches will operate correctly.

[Danny D'Amico]

I think the lockout timer and spark ignitor are two different things:

Here is the spark igniter (I think):

Here is the lockout timer (I'm sure - because it says so):

The PDF doesn't describe the lockout timer; but there is a schematic pasted on the inside of the furnace door that purports to describe it:

I'm still not sure how it works though - but maybe it is the culprit...

I'm getting close because, for a while, tonight, it was all working:

But, then it stopped as soon as I accidentally allowed the door switch to spring open (I bumped it while trying to measure voltages).

[Danny D'Amico]

I think the blower was running constantly at that time, so, I must have opened the door to stop it from running ...

[Danny D'Amico]

Something I did must have worked, at least temporarily, because I got pilot light finally tonight:

And then I got main burner:

And then I got blower:

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 ...

[Danny D'Amico]

After wiggling and tapping everything I could on all the connections and circuit boards, I was able to get the full sequence of clicking, pilot lighting, burners lighting, and fan blowing.

But, the furnace seems to shut down too quickly; like after a minute or two. Then I can't get it restarted again.

I will test again in the morning.

[Danny D'Amico]

I'm confused as most people said to jumper R & W, not W & C. Plus, there are two W wires!

Which W would you suggest I jumper to C?

[Tony Hwang]

[Danny D'Amico]

Here's what I've identified, so far:

This is the "3-wire pilot assembly":

This is the high-voltage ignitor:

This is the "gas valve" (I tapped on both solenoids):

This is a fusible link and something called a "lockout timer":

This appears to be the Limit Switch (I can't find the VSSS):

This compartment holds the fan-control PCB:

This is the terminal set from the thermostat (and elsewhere):

This 3 Amp fuse tested good:

This is the "fan control board":

This is the door safety switch:

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

This is the 16x25x1 3M filter:

At the moment, I'm trying to figure out how to test the lockout timer, which might be preventing the propane gas from flowing ...

[Danny D'Amico]

OOps. Red to white!

[Tony Hwang]

Hi, Leave that door open for now and tape down the switch. You may have a intermittent ignitor. This is the one like BBQ lighter. When you hear zapzap sound, you should be able to see spark. Remove the tape and close the cover when problem is solved. Piezo ignitor is known to go bad when old. I used to have that problem in my 5th wheel camping trailer fridge. Only remedy is replacing whole module.

[Danny D'Amico]

This is very interesting.

My wife constantly turns the thermostat off and back on.

Should we be more, shall I say, "graceful" about adjusting the thermostat?h

[Danny D'Amico]

I've been playing with it for a while, and, can't seem to fully reproduce my success. I'm going to hit the sack and attack it again in the daylight.

Seems to me all those *timers* are making a clean starting point difficult, particularly the thing called a "lockout timer"...

I'm starting to wonder if it's a bad thing that the wife loves to turn the thermostat off and on constantly all day, as if *she* is the automatic control!