Low voltage gas valve, please help ready to bang head off furnace!!!

[paintdan85]

Hello guys,

     I bought a used furnace (Luxaire model GM9S100C16UP11A) to heat my garage. Installed it fired it up, inducer fan kicks on, igniter lights up, no flame. After doing some research, the gas valve requires 24v, my leads only are supplying 8v so I figured the board was bad (I have 25v coming off transformer) So I bought a new board $90 shipped (source 1 board model # s1-33103010000) I got it today, installed it and now I'm pulling a constant 12-13volts (checking at board) and still not opening gas valve. I'm at the point that I was thinking about hooking up a relay to the 12-13v coming off the gas valve leads so I can power from a alternative 24v source but realized even when I turn off the thermostat it remains a constant 12v so even a relay wouldn't work. Could I have a bad (new board)? I've been working on this over a week now with 2deg weather outside and I'm ready to throw this furnace out the door.

 

Let me know your thoughts guys!!!

Dan

[16345Ed]

Let me preface... I know next to nothing about furnaces.

But it sounds like it could be an Ignitor issue. 

 

[16345Ed]

Or the flame sensor...

 

[paintdan85]

Well the Igniter glows red during the start up phase so I don't think it would be that, If I supply a foreign 24v to the gas valve the furnace starts up with no problem, and the board flashes 1 red flash, which stands for (flame indicated when there is no call for heat) which tends to tell me that the flame sensor is working because it knows its light up when its not suppose to be (manually holding the gas valve open with foreign 24v)

So that kind of crosses out the igniter & flame sensor idea

Thanks for the ideas

 

Dan

[paintdan85]

Now the pressure switch (the round looking device hooked to the wall of the furnace, im measuring 24v when in start up mode and then it go's away when the thermostat kicks off. So what I did, I jumped a wire off the sensor to the gas valve, then the other side of gas valve to ground.

 

The furnace now works as its suppose to, fires up with thermostat and turns off with thermostat. Long run do you think this is safe to continue running the furnace like this?

 

Thanks

Dan

[AccApp]

Super unsafe to leave this thing rigged up like this. You have a bad board. You know the gas valve works with 24v supplied to it, you know the board needs to supply 24v when it wants the gas valve on and no voltage when no call for heat exists. Triple check all your thermostat connections. 

[Budget Appliance Repair]

From you description I'm not totally clear on how/what you bypassed but it kind of sounds like you bypassed the pressure switch.

Does this board have a indicator light that flashes error codes?   If not then you might have something simple like one of the flame roll out switches tripped, (there can be two or three in most furnaces and usually they have a small reset button in the middle of them).

It sounds like the draft inducer pressure sensor, (the round looking device), is working because if it weren't you usually wouldn't even get to the point of the ignitor glowing.

The usually sequence of start up on a furnace like yours is:
1) House t-stat calls for heat
2) Draft inducer motor comes on and runs usually for a predetermined amount of time, (like around 10-30 seconds as a pre-purge)
3) Pressure sensor sees the negative vacuum caused by  the draft inducer motor
   3a) If Pressure sensor doesn't see any or enough of a vacuum to trip pressure sensor then it will usually error out and not go to next stage
4) Ignitor glows and is usually a timer on the board that will let the ignitor glow for 17 - 20 seconds which it should be hot enough to light the gas
5) Board sends voltage to gas valve to open valve and release gas to burners
6) Burners light
7) Goes in a 6 second flame proving mode, (voltage to flame sensor travels thru flame ions to ground and gives the board a microamp reading).
8) If the microamp reading the board gets is too low for any reason, (no flame, bad/dirty flame sensor, bad ground), it shuts down and retrys.
9) If microamp reading the board sees is correct the burner stays burning - then either by a timed setting on the board or a thermal disc on the blower housing the blower motor turns on forcing the heated air thru the vents.
10) House t-stat is satisfied - burner shuts down
11) Then on a timed setting on the board or a thermal disc opens the main blower turns off.
12) Repeats when house t-stat again calls for heat

Looking up the install sheet for the board you purchased it does have the diagnostic led and also a button to recall the last 5 errors the board has recorded, have you read the instructions that came with the new board and used these features?  I don't see any where in what you have described so far that you have done this - it should point you to the source of your failure.

 

[paintdan85]

Hello guys thanks for the info so far!

 

AccApp : I've checked the thermostat connections 15 times over, all the connections on the heater board and thermostat line up. I did not take the wire off the pressure sensor, I just added a jumper from the sensor to the gas valve.  (when the thermostat is not calling for heat, I have no voltage on the sensor, when the thermo calls for heat, I get 24v on the sensor which then opens the gas valve. When the thermo turns off because room is warm enough, 24v is then turned off to sensor which in turns cuts off the gas valve and the blower stays on for another min and half for cool down and then furnace is off, again no voltage at gas valve so it is shut off at that point) So I don't have running gas when there is no call for heat, During the furnace running though, it blinks the error code, flame indicated when there is no call for heat. When the furnace kicks off, the error code go's back to normal green flash no problems

 

Budget appliance repair: I didn't bypass the pressure sensor, its still hooked up as normal, I just jumped another lead from the pressure sensor to the gas valve (I only have voltage on the sensor when thermo is calling for heat, as soon as room gets to temp, thermo kicks off, voltage drops to 0 and gas valve kicks off, and normal shutdown process) I do pull a error code on board when in operation 1 red flash, which stands for (flame indicated when there is no call for heat)  after the thermo kicks off, furnace shuts down and the board go's back to blinking green as no problems.

 

I get to step 4 fine and the glow plug heats on for 15 secs, off for 5 back and forth about 5-6 times and the furnace locks out.

 

The thing is, the old board supplied 8v to the gas valve whether there was call for heat or not, the new board supplied 12v constantly whether call for heat or not. I'm not a Hvac guy but my general sense of electronics is telling me that I should have no voltage when no call for heat and 24v when call for heat. Am I wrong or dose it sound like I got a "new bad board"?

 

Dan

[Budget Appliance Repair]

Did you find and check, (push the reset button), on all 2 or 3 flame rollout and safety switches)?

These:

Did you leave every thing hooked up without the jumper wire and let it go thru a light up cycle till it locked out and then read the error code from the flashing led?  Does your board have a button label "Last Error Code"?

If you have that button and don't have the techsheet that tells how to use it and what all the error codes means here a copy I found doing a quick Google search: http://www.upgnet.com/PdfFileRedirect/035-22285-002-B-0914.PDF

Sounds like you have a bad pressure switch or draft inducer motor not inducing a draft when it starts up - but if I'm remembering correctly then you shouldn't get to the point of the ignitor turning on.

Have you checked the pressure switch, meter on ohms setting, at lease one wire removed from pressure switch, each meter lead to a pressure switch terminal.  Then suck into pressure switch hose gently and meter reading should go from open to closed reading, (this just verifies that the switch will open but you still don't know if it opens at the correct vacuum or something is causing a low draft condition so the switch is doing it job by not opening.  The hose or the port the hose attaches to can also get plugged up.

 

 

[AccApp]

You should also check the circuit from the control board to the gas valve for continuity with the power off. 

[paintdan85]

Hello Guys,

 

Thanks for the help, Ok I checked the two roll out switches good, I checked the pressure switch and it works fine when sucking and blowing into both tubes, the continuity setting on my meter beeps when closed and no beep when open, so I know the pressure switch is working, I also checked for continuity on the gas valve with no power and it is also fine. I got another new board hooked it all back up and it works!

 

So I believe everything is now connected how it should be and it is all working at this time!

 

 

One last question for you guys,

 

I put in this furnace in to replace a vent less wall heater that I got (vent less was putting to much moisture into the air  (1/2gal per hour at what I looked up online) and I was getting black mold all over the ceilings up the wall on a one month old garage) 30,000btu and It would only keep the garage about 50deg running almost constantly, hence the reason why I bought this 100,000btu forced air.

I've seen online that these forced air furnaces create dry heat, I was hoping to dry the air as I was heating the garage, I know I'm getting a lot of condensate from this furnace drawing vented air from outside, could I vent the furnace from inside the garage to help pull moisture from the air also? Or should I keep it vented outside? (this in the incoming combustible vented air, not the exhaust)

 

Thank you guys!

Dan

[AccApp]

2 hours ago, paintdan85 said:

I've seen online that these forced air furnaces create dry heat, I was hoping to dry the air as I was heating the garage, I know I'm getting a lot of condensate from this furnace drawing vented air from outside, could I vent the furnace from inside the garage to help pull moisture from the air also? Or should I keep it vented outside? (this in the incoming combustible vented air, not the exhaust)

A common misbelief, furnaces on their own do not add or remove moisture from the air. 

You would lose a little efficiency and maybe pull a very small amount of moisture from the conditioned air if you kept venting the exhaust outside and drew combustion air from inside. You would still need air coming from outside to make up what was used.

 

I’d recommend keeping it as a direct vent appliance.

[paintdan85]

Perfect I will leave it vent outside, thank you again for all the help guys!!!

 

Dan