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

[Stormin Mormon]

Blue flame is desired. Orange suggests some thing mixed in with the flame. Rust, maybe.

[Stormin Mormon]

My guess is, that the tubes that carry the gas air mix into the burner box are tilted. And that burner 4, is full of rust.

[clare]

They were made for natural gas, which is lighter than air and dissipates in event of accidental release, while propane (lpg) is heavier than air and settles in the low spots - so the lockout timer is used to prevent ignition before the possible accumulated gas is dissipated.

[Irreverent Maximus]

Quit being so anal.

[Stormin Mormon]

I can't help but hang onto things. Up yours! Butt out. ;) That was slick!

[Irreverent Maximus]

Actually, the timer times open, meaning that it activates when the pilot fails to light. This prevents the pilot valve from filling the combustion chamber with propane and subsequent ignition via the pilot igniter. The timer has a manual reset. Something else for you to keep track of in case the unit does not start.

This timer is only for the use with LPG (propane). One of the reasons I disagree with the installation manual's statement to discard the old parts. It would be preferable to keep the old in a bag, with instructions, so that the unit may easily be converted back to natural gas. In your case this might not be a big deal, but I know for certain that if I had the chance to switch to NG, I would do it in a heartbeat. Cheaper to operate.

Oh, tell the wife that she is not a thermostat. Let the thermostat do its job. That and to make you a sandwich and bring you a beer. :-)

[clare]

Having the timer on for Natural Gas would most likely not be an issue - just not REQUIRED, like it is for Propane.

[Irreverent Maximus]

Fargin' dangleberry. :-)

[Danny D'Amico]

The interesting thing is that this lockout timer isn't needed for the non-propane gas burners. Propane, apparently, is different that way, for a reason I'm still trying to ascertain.

But, here's one description of what it does:

During normal operation, if the pilot flame is not proven within approximately *30 seconds*, the lockout timer opens, de-energizing the gas valve and stopping the gas flow to the pilot. The lockout timer will remain open until it is manually reset".

Notice the time period is hugely different in this document:

"During normal operation, if the pilot flame is not proven within approximately *5 minutes*, the lockout timer opens, deenergizing the gas valve and stopping the gas flow to the pilot. The lockout timer will remain open until it is manually reset".

In summary, the lockout timer apparently shuts the system down if the pilot flame isn't proven in the allotted time frame.

[Danny D'Amico]

I probably am confused.

Whatever gas the furnace was originally intended, is a different gas than propane, such that, if the furnace is converted to propane, this lockout timer is needed.

[Danny D'Amico]

Ah! Finally. An explanation! Thanks!

So, if the pilot flame doesn't prove itself, then the lockout timer will shut down the system after the allotted time has expired.

That makes sense.

[Irreverent Maximus]

True, but one still needs the orifices. Swap out the orifices plus MGV spring, then swap a few wires and the system is 100% NG. The wiring takes about 2 minutes (if one is slow). Some tweaking on the MGV output will be necessary, too...

[Danny D'Amico]

Finally this lockout timer makes sense. If the pilot doesn't light, and if the gas is propane, which is heavier than air, the timer times open, so that the leaked propane isn't ignited. Makes sense now.

However, I would think NG would still have the same problem, even though it's lighter than air, if it filled a room.

Interesting. I have no idea what the difference is, but, as you noted, I don't have a choice since trucks deliver the propane to my tank outside.

[Danny D'Amico]

Good to know.

I was wondering why it wasn't there for NG, but *only* for propane.

The discussion revolved around the fact that NG was lighter than air, yet, propane wasn't. So it filled the room differently.

[Danny D'Amico]

From what people said, propane is apparently heavier than air, while NG is lighter than air.

[Irreverent Maximus]

[Danny D'Amico]

LESSONS LEARNED on my Payne 394JAW propane furnace this week:

Voltage between R & C should be 24VAC.

- Red = 24VAC power (sometimes called RH, for Red Heat, RC for Red Cold)

- C = common (often blue, or black), usually not switched

The typical color code is:

- White = heat

- Green = blower

- Yellow (sometimes blue) = Compressor

- O = Orange (heat pump)

A typical test would be:

- Connect R to W to tell the furnace to supply heat.

- Connect R to Y to tell the system to supply cooling.

- Connect R to G to tell the system to operate the fan.

Most common problems:

1. It's (usually) not the thermostat
2. Sticking 3-wire pilot assembly (common, low stage, high stage)
3. Power to the two-stage gas valve (which is only on 4 to 7 seconds)
4. Spark igniter (high voltage comes out to light pilot)
5. Gas valve (sticking or blown solenoids)
6. Fan control board (often a relay sticks or won't turn on)
7. 3A fuse on the blower circuit board
8. One of the safety mechanisms has tripped

The thermostat "calls for heating" by connecting Red to White.

Power goes from the 24VAC Transformer to the Fusible Link to the Limit Switch to the Vent Safety Shut-off Switch to the Lockout Timer to the pilot ("pick" & "hold" gas valves), enabling propane gas to begin flowing in the pilot.

Power also flows to the high-voltage igniter, which clicks a few times to ignite the pilot flame.

About 60 seconds after the pilot lights, the safety pilot switches its contacts and energizes the main valve portion of the gas valve.

About 10 seconds later, the main gas valve opens, and the main gas is ignited by the pilot flame.

About 75 seconds after the pilot lights, the fan control board activates the blower 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.

a) If the furnace overheats, the Limit Switch opens. b) If the furnace overheats in the vestibule, the Fusible Link opens. c) If the furnace overheats in the vents, the Vent Safety Switch opens. d) If the pilot doesn't light, the Lockout Timer shuts down the system. e) If the door is opened, the 120VAC door switch turns off the power.

These are the thermostat connections:

This is the "3-wire pilot assembly":

This is the high-voltage ignitor:

This is the "gas valve" (set up for propane):

This is a fusible link, vent switch, & the "lockout timer":

This is the limit switch:

This compartment holds the fan-control PCB:

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

This is the 3 Amp fuse for the fan-control PCB:

This is the "fan control" PCB:

This is the 120VAC door safety switch:

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

This is the on/off mechanism (pull the plug) for the 120V power:

This is the 16x25x1 3M filter:

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

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

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

This is a furnace operational and troubleshooting manual::

This is the burner running and heating up the house:

Maintenance:

- Check the air filter & clean with water monthly.

- Clean & lubricate blower wheel yearly.

- Clean the pilot area and clean the sensing probe yearly.

- Lubricate the motor with 20-weight oil every 2 to 5 years.

- Clean heat exchanger with brush & vacuum when necessary.

Thanks to all of you, this one furnace is not only working, but, it's finally starting to make sense how it works.

Your help in this endeavor was/is much appreciated.

[Danny D'Amico]

Ooops. I forgot to mention the 120VAC blower speeds, which are usually set lower for heating than for cooling:

- White = neutral

- Red = low speed

- Yellow = medium low speed

- Blue = medium high speed

- Black = high speed

[Danny D'Amico]

Final update ... everything seems to be working fine now that the weather has gotten warmer! :)

It's 59 degrees here in San Jose today.

I set the blower to 80 this morning, just to make it turn on, and it went on.

The only thing I wonder about is how *gentle* I should be with the thermostat. I already admonished the wife to stop shutting off the switch - but - should we always gently turn the thing or doesn't it matter much?

I'm afraid of getting caught in one of those timeout situations, and having the board hang up as a result (which might have been what had happened all along).

[The Daring Dufas]

Danny you can switch to an electronic thermostat for very little money and use the mercury switches from your old one for the next bomb you build. The electronic thermostats have a built in time delay for their operation which really protects your system by preventing "hammering" of the control circuit. A time delay is really more important for air conditioning since turning it on and off repeatedly will cause a great deal of stress on the compressor. I install a timer in AC condensers for customers who have an older mechanical thermostat to prevent the compressor being turned on and off repeatedly, I use a 3 minute delay. An electronic thermostat usually has a programmable time delay and an offset temperature that can be programmed. You can program you're new thermostat so it operates at a different temperature than the one on the display. You could install a thermostat inside the return air duct but leave the old thermostat on the wall for your wife to fiddle with. ^_^

TDD