York Diamond 90

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Old 01-30-12, 09:37 AM
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York Diamond 90

I've read what I can find on this furnace here, but my problem has a twist to it.

I have a programmable thermostat that is about 15 years old, it was put in when the house was built as was the York Diamond 90 furnace. I have the thermostat set so that between 10pm and 5:30am the threshold is 55 degrees to request heat. So there should be no call for heat during the night. Normally (because we live in the temperate NW) the house temp will drop to the 66-67 degree area.

What does happen is that the furnace blower fan will come on and blow air and it keeps on blowing until I go down to the basement and throw the switch to turn off power to the transformer that supplies 24v. When I turn it back on it is fine.

The furnace operates fine otherwise and when the thermostat really calls for heat it works just as it should.

I can understand it blowing cold air if there is a failure to ignite and so on, but there should be no call for heat at all which has me stumped.

Help?
 
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Old 01-30-12, 10:15 AM
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I'd start by checking the thermostat to see if their is any indicator suggesting why the fan is turning on.

Do you have the instruction manual for the thermostat? Read that, too.

Unfortunately, digital thermostats can have all manner of bells and whistles and some can be programmed to do a variety of things that appear to be odd.

Just as an example, some localities require that fans be turned on periodically to purge the dwelling of stale room air that might be contaminated.
 
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Old 01-30-12, 10:37 AM
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I have the booklet for the thermostat but it pretty much just deals with setting it. (No install instructions)

During the warm summer we sometimes run just the circulation fan in the furnace to pump the cooler basement air (in the ducts) through the house. (No AC)

I was hoping to figure a way to disconnect the switch part of the thermostat that turns just the fan on, but haven't had much luck figuring that out.

It's a Honeywell thermostat and I went to their page to see if they have an install manual, but all the have is the same booklet I have for download.

It has three wires that run down to the furnace. They look like telephone hook up wires
 
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Old 01-30-12, 10:56 AM
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Now it is doing it during the day. I also have it set to be (essentially off) between 8am and 5pm

It just did it, and I went and it was flashing 1 flash (1 sec on 1 sec off)

According to my manual....

This indicates that the flame was sensed when there was not a call for heat (that fits) With this fault code the control will also turn on both the inducer motor and the supply air blower. (yes it seems to) This fault would typically be caused by a gas valve that leaks through or is slow closing.

I guess I should focus on the gas valve?
 
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Old 01-30-12, 12:08 PM
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<<This indicates that the flame was sensed when there was not a call for heat (that fits) With this fault code the control will also turn on both the inducer motor and the supply air blower. (yes it seems to) This fault would typically be caused by a gas valve that leaks through or is slow closing.

I guess I should focus on the gas valve?>>


Ummm. Interesting code.


The flame sensor is typically energized anytime the inducer motor runs. If there is a burner flame impinging on the flame sensor, presumably the cicuit board can detect that flame.

If it's detecting a flame before or after the gas valve is energized, presumably that code would be generated. Suppose the gas valve was electrically turned off but didn't close and the burners remained lit. The circuit board would detect this and generate the code.


As a practical matter most gas valves these days have dual shutoffs and such a thing is VERY unlikely. Even if it did happen, generating the code can't do anything about a valve that's already stuck open.

The burners would need to remain lit in order to generate the code if my theories are correct. Just gas leaking past the valve could not be detected by the flame sensor.

I suppose it's worth checking to see if the burners are shutting off promptly when the thermostat shuts the furnace off or is turned down.

Sounds a lot more like a bad circuit board than a bad gas valve to me.
 
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Old 01-30-12, 12:31 PM
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It's making me crazy

It works just fine when the thermostat calls for heat. It's when it doesn't call for heat that it acts possessed.

I'm seeing prices for main boards that vary widely. From less than $100 to $350

Do they even make the original main board any more?
White-Rodgers 50A50-241 according to the paperwork in the envelope.

I'm over in Poulsbo. Know any really good techs over here?
 
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Old 02-01-12, 10:19 AM
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Once I got 11 flashes which is puzzling because my book only goes to 8. On the furnace door there is a sticker that has the mysterious 11 flashes recorded as "Broken Roll Out Wire"

Removed main PC board (P031-01267-001) and inspected it. On the upper right corner of the board is a plastic plug in with 4 pins. I gently wiggled that connector back and forth looking with my jeweler's loop and saw that the traces of the board were cracked and not making contact with the pins. Soldered jumpers from the pins to the next component on the trace. 2 of those 4 pins went to the "Neutrals" header on the board. One pin went to relay "K5" one went to the "Hum" connector.
Reinstalled it and did a simple test of calling for heat and it worked. Then went back to "Resume Program" and it shut down appropriately.
The real test will be tonight.
 
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Old 02-02-12, 06:55 AM
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Seems to be working properly now. I guess the fix has worked

Probably buy a spare board just to keep around in case they quit making them. Although I will add some epoxy (etc) around the base of that connector to keep it stable and prevent it from breaking loose from the traces
 
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