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

Page 7 of 9  
On Tue, 10 Dec 2013 19:01:35 -0600, philo wrote:

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.
http://farm8.staticflickr.com/7427/11318411706_f7ceb36cd5_o.gif
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.
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On Tue, 10 Dec 2013 18:01:05 -0700, Tony Hwang wrote:

Here's what I've identified, so far:
This is the "3-wire pilot assembly":
http://farm3.staticflickr.com/2812/11315204683_458e651e36_o.gif
This is the high-voltage ignitor:
http://farm6.staticflickr.com/5493/11315212966_6c04b85a9f_o.gif
This is the "gas valve" (I tapped on both solenoids):
http://farm8.staticflickr.com/7358/11315269874_54fbde6523_o.gif
This is a fusible link and something called a "lockout timer":
http://farm8.staticflickr.com/7323/11315342803_5356224304_o.gif
This appears to be the Limit Switch (I can't find the VSSS):
http://farm3.staticflickr.com/2814/11315574703_f10de1c8bd_o.gif
This compartment holds the fan-control PCB:
http://farm6.staticflickr.com/5503/11315391333_02351134b4_o.gif
This is the terminal set from the thermostat (and elsewhere):
http://farm3.staticflickr.com/2849/11315437344_17e7793ca9_o.gif
This 3 Amp fuse tested good:
http://farm4.staticflickr.com/3759/11315352135_59c03444e1_o.gif
This is the "fan control board":
http://farm8.staticflickr.com/7443/11315520763_a1bf7cb9e1_o.gif
This is the door safety switch:
http://farm4.staticflickr.com/3789/11315520045_9e1f88de9a_o.gif
This is the on/off switch for the gas, which remains on:
http://farm8.staticflickr.com/7295/11315367933_eb4cc8b179_o.gif
This is the 16x25x1 3M filter:
http://farm3.staticflickr.com/2814/11315620166_f17ba0ef50_o.gif
At the moment, I'm trying to figure out how to test the lockout timer, which might be preventing the propane gas from flowing ...
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On Tue, 10 Dec 2013 16:12:10 -0500, David L. Martel wrote:

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 ...
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Was the blower running at this time?
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On Tue, 10 Dec 2013 18:46:02 -0600, Irreverent Maximus wrote:

I think the blower was running constantly at that time, so, I must have opened the door to stop it from running ...
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On Tue, 10 Dec 2013 16:12:10 -0500, David L. Martel wrote:

The stove and hot water heater are burning fine, and the propane tank is nearly full; and the valve is in the "on" position; so, I can pretty much assume I have gas.
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On Tue, 10 Dec 2013 16:12:10 -0500, David L. Martel wrote:

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.
http://farm3.staticflickr.com/2814/11315574703_f10de1c8bd_o.gif
If the furnace overheats in the vestibule, the Fusible Link opens.
http://farm8.staticflickr.com/7323/11315342803_5356224304_o.gif
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:
http://farm8.staticflickr.com/7323/11315342803_5356224304_o.gif
The PDF does not explain how that lockout timer works though ...
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Looking up why a propane furnace needs a lockout timer, I find that they want the gas to be cleared from the pipes *before* igniting the pilot (hence why the lockout timer is a normally open switch).
It seems to say so, on the last sentence, of this document: http://xpedio.carrier.com/idc/groups/public/documents/techlit/58se-11si.pdf http://xpedio.carrier.com/idc/groups/public/documents/techlit/40394dp40-a.pdf
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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. :-)
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On Wed, 11 Dec 2013 21:11:09 -0600, "Irreverent Maximus"

issue - just not REQUIRED, like it is for Propane.
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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...
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On Wed, 11 Dec 2013 21:11:09 -0600, Irreverent Maximus wrote:

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.
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On Wed, 11 Dec 2013 22:22:45 -0500, clare wrote:

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.
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On Wed, 11 Dec 2013 22:32:47 +0000, Danny D. wrote:

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:
http://xpedio.carrier.com/idc/groups/public/documents/techlit/58se-11si.pdf 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: http://xpedio.carrier.com/idc/groups/public/documents/techlit/40394dp40-a.pdf "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.
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On Thu, 12 Dec 2013 03:33:00 +0000, Danny D'Amico wrote:

From what people said, propane is apparently heavier than air, while NG is lighter than air.
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http://www.engineeringtoolbox.com/gas-density-d_158.html
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On Tue, 10 Dec 2013 16:54:27 +0000, Danny D'Amico wrote:
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: 0. It's (usually) not the thermostat 1. Sticking 3-wire pilot assembly (common, low stage, high stage) 2. Power to the two-stage gas valve (which is only on 4 to 7 seconds) 3. Spark igniter (high voltage comes out to light pilot) 4. Gas valve (sticking or blown solenoids) 5. 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:
http://farm8.staticflickr.com/7395/11312016114_3f61f28c11_o.gif
This is the "3-wire pilot assembly":
http://farm3.staticflickr.com/2812/11315204683_458e651e36_o.gif
This is the high-voltage ignitor:
http://farm6.staticflickr.com/5493/11315212966_6c04b85a9f_o.gif
This is the "gas valve" (set up for propane):
http://farm8.staticflickr.com/7358/11315269874_54fbde6523_o.gif
This is a fusible link, vent switch, & the "lockout timer":
http://farm8.staticflickr.com/7323/11315342803_5356224304_o.gif
This is the limit switch:
http://farm3.staticflickr.com/2814/11315574703_f10de1c8bd_o.gif
This compartment holds the fan-control PCB:
http://farm6.staticflickr.com/5503/11315391333_02351134b4_o.gif
This is the terminal set from the thermostat (and elsewhere):
http://farm3.staticflickr.com/2849/11315437344_17e7793ca9_o.gif
This is the 3 Amp fuse for the fan-control PCB:
http://farm4.staticflickr.com/3759/11315352135_59c03444e1_o.gif
This is the "fan control" PCB:
http://farm8.staticflickr.com/7443/11315520763_a1bf7cb9e1_o.gif
This is the 120VAC door safety switch:
http://farm4.staticflickr.com/3789/11315520045_9e1f88de9a_o.gif
This is the on/off switch for the gas, which remains on:
http://farm8.staticflickr.com/7295/11315367933_eb4cc8b179_o.gif
This is the on/off mechanism (pull the plug) for the 120V power:
http://farm6.staticflickr.com/5477/11327971174_cd6604d692_o.gif
This is the 16x25x1 3M filter:
http://farm3.staticflickr.com/2814/11315620166_f17ba0ef50_o.gif
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
This is a furnace operational and troubleshooting manual:: http://xpedio.carrier.com/idc/groups/public/documents/techlit/40394dp65-a.pdf
This is the burner running and heating up the house:
http://farm4.staticflickr.com/3832/11327898655_e38c974a9b_o.gif
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.
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On Thu, 12 Dec 2013 04:40:32 +0000, Danny D'Amico wrote:

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
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On Thu, 12 Dec 2013 04:53:36 +0000, Danny D'Amico wrote:
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).
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On 12/13/2013 6:54 PM, Danny D'Amico wrote:

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
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