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Dallas Wilm 10-07-2011 03:31 PM

York Diamond 80 Not Igniting
I just bought a house and it has a York Diamond 80 P4HUA12N06401A furnace. I am unfamiliar with this make/model and am just wondering if the fan is supposed to run continuously as this one does.

I found that if I cranked the thermostat to max and watched, the furnace will ignite and run for about 20 minutes and then shut off. Then when I return the thermostat to normal it seems that the fan cuts in and then just runs forever without heat until I crank it to max again.

The old mercury thermostat doesn't appear to have a fan control on it just temperature.

Is this a problem with the furnance or the thermostat?

Doc Holliday 10-07-2011 07:06 PM

At this point it could be either. It sounds as if at some point the high temperature limit switch is tripping and possibly resetting.

Try installing a new basic digital stat and see what happens.

Dallas Wilm 10-07-2011 08:20 PM

Ok, I have replaced the old mercury switch thermostat with a Honeywell 5-1-1 Programmable Thermostat and initially when I turned the furnace on it lit and the fan came on. Then after about 30 mins the burners went out and the fan continued to run and is still running now after about an hour.

biggles 10-07-2011 08:25 PM

check your fan setting on the new stat make sure its in auto,so the fan runs 24/7 ....its the unit as said.if you reset the 115V toggle on the side of the furnace does the fan stay off until the next heat you have a solid stat control board within the furnace?

Dallas Wilm 10-07-2011 08:28 PM

The thermostat only has R and W. There was no G wire for fan control coming out of the wall.

beenthere 10-07-2011 08:30 PM

Check your air filter, may also have a dirty evap coil if you have central A/C on the furnace. Afte checking those things, if it still does it, probably has a weal high limit switch due to running on high limit too often.

Dallas Wilm 10-07-2011 08:40 PM

I changed the air filter in it last week and we do not have central air. I checked for the high limit switch my coworker said that this model has an electronically controller limit switch.

I was just playing around with it and with the fan still running I cranked the heat as high as it would go and the burners did not light. I removed the lower access panel which has a safety switch that shuts down the furnace, then after putting it back on the fan fired up and the burners then lit up. They stayed on until the thermostat was satisfied and then the burners went out but the fan remains on blowing cold air.

biggles 10-07-2011 08:50 PM

your fan is timed delayed off the control board the contacts are welded together on the small relay on that board...remove the R stat wire off the board or going into the furnace :wink:nothing should run

Dallas Wilm 10-07-2011 08:59 PM

I disconnected the R wire and the fan still continues to run. It seems the only way to get the fan to stop is to either flip the breaker or trip the safety switch on the access panel.

Another thought, on the control board there are connections for R W Y G etc, if I ran a wire from the G up to the G connection on the thermostat would this give me fan control?

thestig3 10-07-2011 09:14 PM

G from furnace to t'stat would give you fan control. You should have a sightglass on bottom panel and you should be able to see the red indicator light. Count the # of flashes fault codes should be on the control module. Should be able to narrow it down from there.

beenthere 10-08-2011 04:18 AM

The high limit on your furnace is a small mechanical switch.

Did you install a new thermostat in the last year.

Dallas Wilm 10-08-2011 07:28 PM

Ok, I connected a wire from the G connection in the furnace to the G connection on the t-stat and now it appears to be working correctly. The fan cuts in, the burners ignite, then when the burners go out the fan runs for about a minute and then also cuts out. Thanks Guys.

thestig3 10-08-2011 10:42 PM

When you say fan cuts in do you mean small inducer motor near burners or blower motor that circulates air in the house? If blower motor, tstat may be set to electric heat causing motor to energize on a call for heat. No biggie you will just get cold air until heat exchanger gets up to temp.

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