Furnace: Arocaire/Int'l Comfort Products Model # NNE100F20A1

[try it now]

Last week I fired up and tested the furnace (installed new in 2001) for the first time this season and it worked fine.  This week it got cold enough to use it and so I turned it on again.  I heard the burners light and the exhaust fan start, and heard what sounded like a solenoid or relay energize, but I never heard the forced air blower start.  I began to smell hot ducts so I shut it all down.

The good news is that my emergency beer is nice and cold with the furnace being down.  The bad news is that my family is nice and cold too.  

The furnace is actually working great except that the blower motor will not start.  I spun it easily with my finger.  There is a pressure switch designed to disable the furnace when the lower door is removed.  When I close that switch I can hear the small hum of current flowing.  When I release it, the humming stops and I can hear a relay click open, about every other time I do that.  That is, sometimes the humming stops without the audible click.  I have no idea if that is signigicant or not.  There is what appears to be a large capicitor that perhaps serves to start the fan motor(?) right out front, and the humming sound modulates slightly when I press on it.  Finally I have inspected the circuit board and all electrical connections and there is no obvious signs of trouble there.  I would appreciate some encouragement that perhaps I can fix it myself this time.  (Repair man was here a couple of years ago to replace the igniter).

[Pegi]

 I do not work on centrals or furnaces, however same principals apply to window units .....does the blower fan run ok when the thermostat is set off of auto to run in cooling mode?  If so the fan motor is fine....same motor....if it does not start running see if it will start if you turn it by hand, if so probably a bad capacitor....

[dkpd1581]

Troubleshoot your unit using the thermostat. 

Turn the t-stat to "OFF" and then move the fan selector switch to "ON".  Do this with the help of another person that way you can be at the air handler with the door switch pushed in.

With the fan "ON" you will know whether the fan is going to run or not.  If it does not come on with the selector moved to "ON", give it a gentle spin with the hand to see if you can get it moving.  If it does start to spin up and run, then it is your capacitor.

You can save all of this effort if you have a meter that measures capacitance.  If the reading is outside of 10% of the value listed on the shell, change it out.

If the indoor blower motor does run with the fan "ON", turn the fan to "AUTO" and have the helper turn the t-stat to HEAT and force a call for heating.  If the motor does not come on within 30-120 seconds, then the fan delay is bad. 

This delay can be a combination fan/limit switch, a timer, a snap disk element.  You will have to see what mechanism it is and troubleshoot from there.

[try it now]

Progress!  My very basic t-stat cannot command fan w/o heat, but following your instructions I was able to start the fan manually.  I waited for the fan delay to kick in and then as soon as I touched the fan I new the motor was energized because of the vibration.  I spun it very gently and could hear it strain to spin up, which it did!

So, if I understand correctly, that means that I need to replace the capacitor, right?

[Pegi]

This is what it is pointing to as the problem, find a replacement that has the same mfd and volts rating that is printed on the one installed now....the mdf rating has to match, the volt ratiing has to be the same or higher...

[appl.tech.29501]

here's one place you can find your cap.

http://americanhvacparts.com/capacitors_search.htm

[try it now]

Thank you, Masters and Sublime Masters of Appliantology.  I purchased a new capacitor for $6.17 today and repaired the furnace myself.  Joining you guys was the best $5.00 I ever spent!  Now my wife thinks I am clever.  Where else can you buy THAT for five bucks?

:dude:

[Pegi]

Cool....errrrr, Heat!  lol, thanks for letting us know that fixed the problem...