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rodge 11-01-2008 06:55 AM

York Stellar Plus won’t ignite
Natural gas furnace, 12 years old, small, only heats 2 rooms,
Sticker says model # M3UF024SA for cooling, P2UDD06N03B01D for furnace, can’t find it anywhere.
When heat is switched on motor starts running, pressure switch (the one on the right with 2 wires) closes (multimeter reads 0V), but hot surface igniter won’t ignite.
Disconnected the igniter and there is no voltage coming in to igniter contacts.
Igniter itself looks OK, not broken, a little charred, ordered new one just in case.
No diagnostic LED here, like our other unit York Diamond 80 has.
What could be the problem, what can I test further myself ?

photo with upper part door open:

kok328 11-01-2008 08:35 AM

For a 12yr old unit, this one looks really clean.
After the pressure switch is made, the flame sensor/ignitor should be energized.
What is the second pressure switch hooked to?
It appears this is not a standing pilot system but, rather an electronic ignition system. Does the ignitor glow red/orange after the pressure switch is made? Does the system just shut down after ignition failure?

rodge 11-01-2008 08:55 AM

Ignator looks like this

If electronic means no pilot light, then it's electronic.
Normally it should glow, but does nothing.
Somethere I read(not about my model), that there should be 115 v coming to ignator. I disconnected the plug and tested and it reads 0.
So the problem between pressure switch and ignator, but what?
The other pressure switch has 3 contacts I dont know what it is for.
I saw video on youtube
how to test pressure switch. they talk about 2 contacts, that's what I have on the right side and it closes(reads 0).

kok328 11-01-2008 01:43 PM

A really stupid question but, are the gas valves on?
I can see for sure but, it appears that the pressure switch on the right is tied to the pressure switch on the left, at least on the clear tubing. The pressure switch on the right is tubed to the inducer motor. I guess we need to see whats going on with the pressure switch on the right. Where do these 3 wires go? Is the ignitor connected to the circuit board?

rodge 11-01-2008 03:31 PM

Gas is on; blue switch inside and red outside.
Pressure switches not connected with each other.
LEFT one(with 3 wires) connected by tube to inducer motor.
Tube from the RIGHT switch(with 2 wires) splits in 2: to top gas chamber and to gas valve(with blue gas switch).
What does it mean and how to test them?

Will check that pipes for inducer and exhaust are clean, they are not meshed on outside.
Could it be the reason for not lighting up?

kok328 11-01-2008 06:18 PM

Sorry, I typed it all wrong. It appears that the pressure switch on the left is tubed to the inducer motor and the other pressure switch on the right. At this point (and I'm not sure why) it appears that York has on pressure switch for the ignitor and one pressure switch for the gas valve?
If the inducer motor is running and maintaining rpm to the satisfaction of the pressure switch then blockage in the exhaust would be irrelevant. I'm sure you already did but, start looking for loose connections, check your ignitor for continuity. If you see any relays, give them a sharp tap while the unit is still in the startup cycle.

kok328 11-02-2008 06:29 AM

Another thought, check for any reset buttons and check for continuity on any limit switches.

rodge 11-02-2008 08:25 AM

There is what I suspect is a limit switch, round with 3 tabs, has too many wires connected, how to check it ?
Checked pipes – clean.
This unit is heating/cooling and cooling is fine, I had to say it earlier - might mean less tests.
Found the control board in lower compartment with diagnostic LED.
Hoped to see it blinking but it’s off all the time, not a blink.

Situation remains:
On call for heat, inducer motor starts and runs and nothing else happens. I let it run for 5 min – nothing, runs until switched off by furnace switch.
My goal it to find the part needing replacement( pressure switch , control board, ???).
I will risk replacing myself anything under hundred bucks.

Right pressure switch has NC and C terminals wired.
Left pressure switch that’s tubed to inducer has NC, NO and C terminals wired.
Tubes clean, no cracks.
How to test their electricals?
What would be the sing of bad control board?

kok328 11-03-2008 10:57 AM

test for continuity on the limit switches and the same for the pressure switches but, test them when the inducer motor is running.
As far as the control board, when all else fails, replace the board but, I don't think we're at that point just yet. I have a feeling it's something really stupid and we'll both be kicking ourselves in the butt when it comes to light.

rodge 11-03-2008 12:18 PM

sure feels like something stupid (disconnected wire), before the pressure switches.
Found troubleshotting manual for control board
Going through chart 1(page 2)
with inducer running there is 25v between C and R on tranformer,
but there is 0V between TR and TH on control board.

Board has no power! Doesn't mean the board is bad.

here is from left to right board, transformer, limit switch.

Does something look strange?

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