fan constantly on - http://www.hvacmechanic.com/ Forums
Original message
| billwright1331
 |  "fan constantly on"
, posted Mon 9 Jun 18:12  
Our furnace fan runs even when we remove the thermostat. It is a 5 year old Heil with Central Air. What might be the cause / fix?
Bill W
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Replies:
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| billwright1331
| "Re(1):fan constantly on" , posted Tue 10 Jun 03:03:
The fan now turns off periodically, then on again. The thermostat is still diconnected. I haven't timed it yet but it seems that the amount of time the fan runs is getting smaller each hour. With the thermostat removed are there any circuits that provide simple logic to any change in conditions? For further info our neighborhood has had a measured official rainfall of 9+" in the past four days. The drain tube going from the furnace to the sewer drain in the basement has been briefly underwater. I would appreciate anybody who can help us fix this without calling an electrician and can offer computer help as paymeny in kind.
Thanks --
Bill W
[this message was edited by billwright1331 on Tue 10 Jun 03:05] |
| | yuri
| "Re(2):fan constantly on" , posted Tue 10 Jun 18:09:
If the limit control opens due to overheating it will turn the fan on to cool off the furnace (logic). If it is faulty or has had water dripping on it from a leaky evaporator coil (remote possibility)/shorting, then that may start the fan. A faulty circuit board may do the same thing but they use fail completely on or off. Pinched tstat wiring may do the same thing but very rare. Excessively high humidity/damp basement can cause corrosion and failure of circuit boards. Had one turn green/solder joints etc and fail. I recommend to LOTS of my customers to get a de-humidifier and set it to 45% for the basement. Have one in mine. Works great. Computer help? Why is Vista so slow and clumsy? Zone Alarm won't work well with my Vista, Norton works okay.
Yuri
[this message was edited by yuri on Tue 10 Jun 18:15] |
| yuri
| "Re(1):fan constantly on" , posted Mon 9 Jun 19:37
Some of them have a continuos run terminal on the circuit board and the installer may have put one of the fan speed wires (usually red) on that terminal. Not dangerous but keeps the fan running for circulation all the time. Terminal should be labeled CONT or something like that. If so you can remove that wire and you must tape the end of it up with several layers of electrical tape or put in on a PARK terminal. It will be live from induced motor voltage. Or better yet get a tech to do an annual service on it and have him do it properly/safely.
Yuri
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