York Affinity 9S Series - no flame

[dmetheny]

My York 9S Series is extremely touchy.....

It is only a few years old.

When the thermostat calls for heat:

-The inducer motor comes on
-The pressure switch closes (I have tested the PS by ensuring it stays closed after the inducer motor comes on through this entire process)
-The ignitor heats up and glows

Now comes the touchy part.....

Sometimes everything works just fine. In fact, even though this problem plagued me all last winter, it has worked just fine this winter....up until this weekend.

I can hear the "click" of what I assume to be the gas switch - however, sometimes the gas will come on and I will get flame for a few seconds, after which it will shut off and the process will start again.....and sometimes, I hear the "click", then immediately (within a second) the inducer motor momentarily stops, the ignitor shuts off, and the whole process starts up again.

To complicate matters, the unit can cycle through this process and NEVER lock out, which means that my ignitor is being heated up roughly every 30-45 seconds all night long. I never get a lockout, therefore I don't get an error code.

The installer (who I don't do business with any more for reasons that I won't go into here) at first told me that since this unit is located in my unheated attic, the problem was due to the fact that it must be installed in an area that doesn't drop below 32 degrees. So.....I walled it in and the small "room" it is in now doesn't usually drop below 50 degrees or so (which is a trick here in Chicago).

So...to sum it up - inducer motor works fine, pressure switch is fine, ignitor is glowing fine, gas switch engages and SOMETIMES provides gas for a few seconds, but sometimes engages then everything "recycles" within 1 second.

I'm cold.....please help.

This is a 2nd unit in our house, which heats the upstairs bedrooms. I've had my problems with the main York in my basement - control panel went out within 6 months of being installed, and right now my inducer motor needs to be replaced (but I've got it working temporarily).

I'm not happy with York at this point.

[HayZee518]

only thing that comes to mind is a weak millivolt signal to the main valve. check the screw in connection to the main valve off the thermocouple.

[dmetheny]

Thank you for your advice!

Now - how can I identify which one that would be? I'm not an HVAC professional....and I have only learned what I know so far out of necessity.

What exactly is a thermocouple, what part does it play in the whole scheme, and how do I find it?

[HayZee518]

check the following site. they have valves listed for the YORK furnace. As you'll see some systems are millivolt, some are 24 volt control. a thermocouple looks like a 1'8th inch copper tubing terminating with a screw on gland and a silver button on one end and a 5/16" tube with two jam nuts on it. this end goes into the flame to detect and generate a millivolt signal from about 250 to 750 millivolts.
Gas Valves - Trane: American HVAC Parts

[dmetheny]

Well...

It doesn't appear that this unit HAS a thermocouple. What is does have is a flame sensing rod towards the right side of the burner element (the ignitor is on the left side).

There is also a rubber vacuum tube that runs from the gas switch to the burner/combustion chamber, connecting to a small nipple on the side of the burner chamber. I had noticed that this nipple was loose (it is tightened to the side wall of the chamber with a nut on each side); once I found this, I was hopeful that vacuum was being lost. No such luck.

I've also noticed that the unit seems to work for one complete cycle if I shut it off for a while (at the thermostat) in most cases, then reverts back to its evil ways.

[HayZee518]

for the sake of trying to find the problem, jumper out the switch that the vacuum line goes to. if you had a shematic of the furnace this would help considerably as I could see how its wired and aid in finding out the sequence of events when it was coming on. the flame sense is a flame rod unit. once a flame is established the gas/air between the flame rod and ground ionizes and conducts as if it were dc. this dc is fed to the electronics to establish a flame - no flame and locks out the burner.

[dmetheny]

Actually...the nipple that the vacuum line goes to doesn't have an associated switch; the line goes from the gas switch to the side of the combustion chamber - the inside of this nipple simply opens up into the chamber.

My guess (and it is simply THAT....a guess) is that this vacuum plays a part in the whole "sealed combustion" system, and is simply a safeguard of some type. I checked the hose and nipple, and they are clear (no obstructions).

Regarding your comment of the flame sensor rod.....I'm having a hard time believing that the unit is shutting off due to the rod not detecting a flame; for the most part, once the gas switch clicks (engages, switches, etc.... ), the system shuts off immediately....within 1/2 second. At those times where the unit actually does fire up, it takes a good second to 1 1/2 seconds for the flame to completely light. My perception is that the system is shutting off much sooner than it would if it were actually waiting to sense flame.

Someone I know had suggested that I try jumpering the pressure switch, just in case there is something wacky going on during the whole process. I'm going to try that in a little while, just as soon as I'm done replacing the handle on my kitchen oven (I'll jumper it once the inducer fan starts blowing) just to make sure it isn't working marginally.

Man...for a computer networking guy, I'm sure getting a crash course in the operation of a furnace lately!!!