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JMattero 10-16-2012 08:14 AM

Day & Night furnace wiring
I am looking for a wiring diagram for an older Day & Night brand gas furnace. There have been many hands in this furnace (rental property I recently purchased) and the wiring makes no sense. The model # of the furnace is 100U-19-C and the serial # is 11070-34803. I am not sure of the age of the furnace. In any case, the furnace has a standing pilot, but no thermocouple. There are two wires coming up from the pilot assembly, and one of those is connected to the gas valve. I am not getting 24 volts out of those two wires, and therefore, the gas valve will not fire up. When I connect 24 volts from the transformer to the gas valve directly, the burners light. My first question is what the two wires from the pilot assembly do? It would seem to me that they SHOULD be sensing that the pilot is lit, and would then allow the gas valve to open. However, if this is some type of flame sensor (rather than a thermocouple), I am not sure how the gas valve would know to turn off. If it makes things any clearer, there is also a relay in the circuit mounted next to the transformer (both inside the furnace cabinet). Can anyone give me instruction on how to troubleshoot this, or where to get a correct wiring diagram? My search on the internet has come up empty. Thanks in advance.

danpik 10-16-2012 10:06 AM

Does your furnace have one of these in the pilot flame? (Powerpile)

Or one of these in the pilot flame? (thermocoouple)

BY the sounds of it you have a powerpile. It is a milivolt voltage output. You will have to read the voltage on a milivolt scale on a volt meter. Should be idealy 750Mv.

JMattero 10-16-2012 05:41 PM

Thanks for the reply. It DEFINITELY does not have a thermocouple, since there is no place on the gas valve to connect it. I do know what a thermosouple is and how they work, since I own a bunch of rental properties and have changed a few of them out. It may have a powerpile, but I am not sure. I can see that the pilot is lit, and I can see two wores coming up from the pilot assembly, but cannot see what part of the pilot assembly the two wires connect to. Out of curiosity, how would a powerpile be hooked up to the heater. This is a very old heater (30 years I would guess) which has no control board. As it turns out, I decided to replace the heater today rather than spending a day or so diagnosing a 30 year old heater that appears to have the wiring rigged. I am only asking the question, so I can understand the powerpile in case I run into that again. My question really comes down to this... if the powerpile is in the flame of the standing pilot, I understand how it would send voltage to the gas valve to tell it to open. What I don't understand is how it would tell the gas valve to shut off. Thanks.

ben's plumbing 10-16-2012 05:45 PM

did you google sr

HVACTECH96 10-16-2012 05:47 PM

You have what is known as a two wire pilot assembly.Uses a bimetal switch that closes when pilot flame heats it up, whice completes circuit to GV.

JMattero 10-16-2012 06:14 PM

Thanks for the reply, but how does that bi-metal switch tell the gas valve to turn OFF if it is always in the pilot flame and always creating millivolts? That is the part I don't understand. Yesterday, in doing the diagnosis, we were able to get the furnace to light by hooking 24 volts directly to it so we know that the gas valve was good. The pilot assembly had a little silver box behind it which is where the wires came from, but there was nothing projecting into the pilot flame (I just learned this after talking to the HVAC tech that I was helping diagnose the heater with). Nothing appeared broken off. As I said, today we decided to trash the old heater, since it seemed that there was no safety on it that would shut the gas down if the pilot went out, and also the fact that it was at least 30 years old, and wiring was rigged. Again, I am just trying to learn what we were looking at in case it comes up on a future repair at one of my rental properties. Thanks in advance.

danpik 10-16-2012 07:50 PM


Originally Posted by HVACTECH96 (Post 1032210)
You have what is known as a two wire pilot assembly.Uses a bimetal switch that closes when pilot flame heats it up, whice completes circuit to GV.

Wow. I forgot all about those. I only ever dealt with one and that had to be 30-35 years ago

HVACTECH96 10-16-2012 08:21 PM

power is supplied to valve from circuit board.believe its a red colored board behind a cover.board is also obselete

hvactech126 10-16-2012 09:37 PM

Those are not safe. There is nothing to shut the pilot gas off it blows out. The furnace needs updated to a standing pilot with a safety system such as a thermocouple.

JMattero 10-16-2012 10:35 PM

Thanks to all of you for your help. As I stated, I decided to scrap the old one and replace it with a new one today. THanks again.

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