York Furnace Problem

I've got a 9 year old natural gas York downflow furnace, with a set-back thermostat. I don't have the capacity in front of me, but it heats a 5 bedroom house.
It's been working just fine, until a few months ago. When the thermostat calls for heat, sometimes it won't go on. Nothing. If I take off the blower cover panel, and press and hold in the momentary blower lockout switch, it will go on. When I release the switch, it goes off, as it should, since this switch is inteded to turn the furnace off when the blower cover panel is removed. I then put the panel back on, which depress and holds in the switch (as long as the panel is on - which is during normal use), and the furnace goes on fine and heats the house to the set tempeerature.
When the house tempereature drops below the set point, and the thermostat calls for heat, 'usually' the furnace goes on. But, when it doesn't, I repeat the steps above, and it's comes back on. Sometimes it'll go for a week without any failures, but sometimes it will fail many times in a row.
I jumped the thermostat, and tried a new thermostat, and have determined this is not the problem.
To take the blower lockout switch out of the equation, I installed a new one, and wired it for always closed, but the same problem occurs. If I push and release (sometimes it has to be done repeatedly during a failure) the switch, opening and closing the circuit, the furnace will come on. It will always come on; sometimes one push, sometimes many.
I had a repairman out (very reputable company), and he suspected the control module. A new module was ordered, and a week later another fellow brought it out to install it, only to find it was the wrong part. Not all bad though, because this fellow isn't all that sure that the control module is the problem. He jumped the thermostat at the control module, and every time he jumped it there, the furnace came on. He thinks maybe a gas control valve, but says that the first repairman should be able to nail down the problem. Is this true, or is this a 'replace parts until it's fixed' job?
One more bit of info: I don't remember for certain, but when the first repairman was out, I do think there was one or two times when he jumped the thermostat at the control module and the furnace didn't come on.
The next time the furnace doesn't come on (tonight), I am going to jump the thermostat at the control module and see if it does come on.
What really has got me stumped is that when it fails, one or more pushes on the (new or old) blower lockout switch will make it work. Everytime.
Any ideas?
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Please clarify what you mean by "control module." Is that within the heater chassis? Or is this something akin to a thermostat, as found in the living space? The "control module" in my forced-air heater is a complex thing. I suppose I could simulate a closed thermostat circuit, at the control module. IT seems your repair man did something like this.

"Thermostat at control module" is unclear to me. I think you mean "thermostat connection terminals at the control module." Well, that tells me that the wiring between the thermostat, and the module, is bad. After all, your actions upon the thermostat, in the living space, were consistently ineffectual. Yet a similar action, with the lengthy wiring between thermostat and control module REMOVED from the process, is effective in consistently activating the heater. You might have also had a bad control module; see below.

THAT'S THE NEW CONTROL MODULE, RIGHT?

That evidences a fault in the OLD control module, too.

So you've got either a flaky interlock switch, or it has shifted in its mount, so that it does not get the right "signal" to change state when the panel is closed. Is this switch a momentary, spring-loaded switch? Is it Hall Effect (magnetically actuated)? So it sounds like you have, or had, three problems. Isolate the interlock switch by lifting its wires from the control module. Then check its continuity, very carefully, under various conditions of panel closure. There should be an unambiguous state change between panel *in place* and panel *removed*. The purpose of the interlock is to prevent operation when the unit is not sealed up. My residential forced-air heater was incapactitated by a panel, slightly ajar. I had to drill and screw, so the panel would not vibrate away from full closure.

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Hi,
The control module, the term used in the furnace parts list, is indeed in the chasis, inside the furnace. It's a pcb with transformers, relays, etc. It is an integral part of the furnace.
Yes, the repairman simulted a closed thermostat condition.
Bruce

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Does your unit have electronic ignition? Do you hear interminable sparking?

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Yes, and no, in that order.
The furnace is in the garage. I'm always down there, esp. on cold evenings, so I do notice that when the ignitor comes on, the gas flows, and the burners light. No problem there.
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Your problem could be simple or complex. Let's hypothesize a simple case. Suppose the high-tension cable that carries high voltage from the controller, to the spark gap, is malfunctioning. A major argument against this is that, according to you and Bubba, your action to reset the controller by cycling the interlock switch invariably enabled the heater to successfully operate. Yet if you were wrong on this point, then the simpler potential faults gain new life. Consider that your spark cable could be arcing to ground...intermittently...perhaps based on proximity of the cable to a sharp metal chassis edge...or even proximity of the cable to the flame sensor wire. Thus the spark would not occur at the pilot site, the flame sensor would disallow main burners to be fueled, etc. You might have an overtemp sensor, or undertemp sensor, that is putting your controller into a lock-out state.
You DID say that your repairman replace the controller, right? You ARE presently using a new controller, right?

and
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No. I said:
"A new module was ordered, and a week later another fellow brought it out to install it, only to find it was the wrong part."
The controller has not been replaced.
Bruce

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Ok. It failed. I removed the wall thermostat, and jumped it at the control module. The furnace didn't go on. While still jumped, I pushed the blower lockout switch in and out a few times, and the furnace came on.
Bubba, the diagnostic light does not blink when a failure occurs. It does have the blink codes shown on the side of the furnace, should I need those. However, it does blink once each time the blower lockout switch is pressed. I assume this is simply due to the reset.
HvacTech2, thanks for your reply. Yes, I certainly hope they can diagnose rather than replace parts until it works, but I'm alread into them for the initial visit at $95. Perhaps I should cut my losses and get another company.
Thanks all, Bruce
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Have voltmeter, will travel. Observe solenoid voltages. Are they activated logically, upon jumping of t'stat terminals at control module? Based on other comments, it sounds like your controller is being told to "shut down"; but resetting controller erases that directive. Perhaps some other safety sensor is faulty, or trying to tell you something.

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John B posted for all of us....

No shit geez
--
Tekkie

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This is Turtle.
Bruce your in Parts changing mode already . You might cut your loses and call a recommended service company to look at it.
TURTLE
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Hi Bruce, hope you are having a nice day
On 15-Feb-05 At About 07:59:12, Bruce wrote to All Subject: York Furnace Problem
B> I've got a 9 year old natural gas York downflow furnace, with a B> set-back thermostat. I don't have the capacity in front of me, but B> it heats a 5 bedroom house.
B> It's been working just fine, until a few months ago. When the B> thermostat calls for heat, sometimes it won't go on. Nothing. If I B> take off the blower cover panel, and press and hold in the momentary B> blower lockout switch, it will go on. When I release the switch, B> it goes off, as it should, since this switch is inteded to turn the B> furnace off when the blower cover panel is removed. I then put the B> panel back on, which depress and holds in the switch (as long as the B> panel is on - which is during normal use), and the furnace goes on B> fine and heats the house to the set tempeerature.
B> When the house tempereature drops below the set point, and the B> thermostat calls for heat, 'usually' the furnace goes on. But, when B> it doesn't, I repeat the steps above, and it's comes back on. B> Sometimes it'll go for a week without any failures, but sometimes it B> will fail many times in a row.
B> I jumped the thermostat, and tried a new thermostat, and have B> determined this is not the problem.
B> To take the blower lockout switch out of the equation, I installed a B> new one, and wired it for always closed, but the same problem B> occurs. If I push and release (sometimes it has to be done B> repeatedly during a failure) the switch, opening and closing the B> circuit, the furnace will come on. It will always come on; sometimes B> one push, sometimes many.
B> I had a repairman out (very reputable company), and he suspected the B> control module. A new module was ordered, and a week later another B> fellow brought it out to install it, only to find it was the wrong B> part. Not all bad though, because this fellow isn't all that sure B> that the control module is the problem. He jumped the thermostat B> at the control module, and every time he jumped it there, the B> furnace came on. He thinks maybe a gas control valve, but says that B> the first repairman should be able to nail down the problem. B> Is this true, or is this a 'replace parts until it's fixed' job?
B> One more bit of info: I don't remember for certain, but when the B> first repairman was out, I do think there was one or two times when B> he jumped the thermostat at the control module and the furnace didn't B> come on.
B> The next time the furnace doesn't come on (tonight), I am going to B> jump the thermostat at the control module and see if it does come on.
B> What really has got me stumped is that when it fails, one or more B> pushes on the (new or old) blower lockout switch will make it work. B> Everytime.
B> Any ideas?
What is happening is called a lockout. when you remove the door you are resetting the control. you would get the same result by turning the wall safety switch off then back on. there is no way to troubleshoot the problem over the net so you should let the company you called figure it out. they should be able to do this without changing unneeded parts.
-=> HvacTech2 <=-
.. *IT IS* documented, look under "For Internal Use Only."
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snip

problem
I think tech2 is right here, you'll need someone to look at it to do the diagnosis. The york guys may be of more help if you were to give the M# & S# of the unit...

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This is Turtle.
If you have read the replys by him and what the techs have said. The service company has went to Plan B which is just Parts change it to death. If you got a gas furnace locking out. It usely is not the board doing it and the tech has said I don't know OK let's change the Board.
TURTLE
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wrote:

Pushing the blower door lockout switch is simply resetting the control board/module. That clears the error until the error returns. You need to find the error. Check to see if the module has a flashing error code when it stops working BEFORE you kill the power to the furnace again. Bubba
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