Blower stays on all day on a Heil furn.

[dj1100rt]

I have a Heil, gas, condensor furnace. The blower stays on forever after a heat cycle. Model #NUGK100DH3. Is this likely to be the fan control and limit or the relay in that same circuit. Unit is a 1989 model.

Thanks,

Dave

[Brew Man]

Hey,

Could be a number if things here.One, it could be the wiring has rubbed itself against the unit and grounded out causing it to pick up 24 v and run continuosly.Fan relay has fried itself shut.Someone bumped the switch to fan on, continuosly.Or Heating anticipator is set wrong.Thermostat in wrong location.We could use a little more info.Have you just moved in ? Has the furnace run fine before?I\ Has anyone worked on this lately?

[dj1100rt]

Have lived here almost 20 years.  No one has worked on it since it was cleaned ~2 years ago.  Fan switch is in the auto position.  This problem actually started at the tail end of the last heating season.  Of course, the blower operates normally on the cooling season.

[Trying to help]

Start by testing your fan limit switch.  It keeps the blower from coming on too soon avoiding cold air from blowing and stays on after the burner kicks off to use as much heat as possible.  Some are time delay, some are temp controlled.  Switching it to cool would allow it to function correctly because it is not in that circuit.  Depending on the system, the fact that it stops blowing in Cool could also indicate the relay is fine.  You will have to do some checks or post a schematic to be sure.  

[dj1100rt]

I have a digital ohm meter.  What is the testing procedure?

Thanks,

Dave

[hvacdrd]

The parts breakdown indicates your furnace uses a fan/limit control ICP p/n 1002743 (or Honeywell L4064W1098). It is located above the burners, likely in the center of the compartment. This is a simple helix bi-metal coil that makes & breaks 2 sets of contacts as it heats or cools down. This one also uses a "heat assist" feature which will turn the fan on after approximately 20-90 seconds after the thermostat calls for heat.   

Make sure the white button located in the lower left of the control (if equiped) is pulled out. You can start by adjusting the fan off setting to a higher temperature. Normally these are set around 90'F. If the control fails to turn off the blower then it is time for a replacement. Here's a picture so you know what you are looking at...