York Gas Furnace Blower Runs Too Long

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  #1  
Old 10-11-00, 11:52 AM
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The blower on my York gas furnace seems to be running long after the gas shuts off. After the gas shuts off, cool air blows from the vents and the blower eventually shut off (over an hour). When I first noticed the problem, I went to the basement and took off the front panel. The fan cut off as it was supposed to do. When I put the panel back on the fan did not turn back on again until the gas turned on again. This problem does not appear to happen all of the time. We have noticed that the problem may be occurring during a program change in our electronic thermostat (eg from wake to sleep or sleep to wake). This could just be coincidence. We don't seem to notice the problem during the day. Any suggestions would be appreciated.
 
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  #2  
Old 10-11-00, 03:35 PM
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Hi Bradley:

I think you're on the right track. Some programmable thermostats are called power stealing models and can be incompatible with some furnace boards. [Honeywell T8600 series is an example] The problem with the power stealing models is usually false starts of the combustion air motor. If the thermostat is one of the value brands like LUX or Maple Chase, you may be money ahead to just replace it. First, make sure you have a fresh battery. A weak battery will make digital t-stats go nutso. If that isn't the solution, then you probably have a malfunctioning control board, but my money is on the t-stat. Let us know how you make out. Thanks. John.
 
  #3  
Old 10-18-00, 11:01 AM
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Bigjohn,
Replacing the battery didn't work. Since the time I posted the original message the blower now runs continuiously. Even when I turn the thermostat to off. I now have to remove the front panel of the furnace to shut the blower down. Looking at the wiring diagram it appears that it could be either the thermal board or the blower relay. Are there any tests that I can do to determine which is the problem or do you know from the description of the problem. Any help would be appreciated.
 
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Old 10-18-00, 03:19 PM
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Hi Bradley:

It's a little hard without having the wiring diagram to look at, but you can try disconnecting one device and then turning the furnace back on to see if the blower is off. If not try the other device. Most all modern furnaces are configured to run the blower full time if the high temperature limit switch is open. You may have a limit that has failed. If you can determine which switch is the limit control, take one wire off, then turn the power back on and see what happens. See if you can tell which control system your furnace uses. [ie: White-Rodgers, UTEC, Honeywell] What I mean is the control board, see if you can determine what brand it is. I have a manual that covers most control boards and ignition systems and maybe we can figure it out that way. If you have a scanner, try posting the wiring diagram as an attachment. If I could see the diagram it will help. Also, look in the furnace where the wires come in from the thermostat. Have someone hold the furnace door switch closed and test for voltage between G and C terminals with everything on the thermostat turned off. If you get 24 volts, you probably have a bad thermostat. Remove the wire that comes from the thermostat to G terminal [in other words, remove it from G terminal in the furnace, it should a green wire] and see if the blower now goes off. If it does, replace the thermostat. Thanks. John.
 
  #5  
Old 11-09-00, 02:28 PM
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Bigjohn,

It was the limit switch. I replaced it three days ago and it has been working fine. Thanks for your help.

Brad
 
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