Whirlpool furnace control board question
If, by a hum, you mean a 60Hz hum like that you'd hear by putting your ear to a wall 'former, then I'll go out on a limb and say that, from your schematic, no mechanical motor or sensor could respond that fast. A small relay armature could possibly, though.
With a helper 10' away, you can use an empty garden hose to isolate the noise source to within an inch or so.
Scope waveforms from the control board should show an oscillation, but getting a control board schem. will be difficult.
The current draw should also show this oscillation and will give you a clue as to how many amps are being switched on and off. If the fuse hasn't blown you can use it as a current sensing resistor by measuring the voltage drop across it, but your scope will have to be isolated from ground.
I guess there is also a remote chance that the 'stat could be causing this behavior.
You'll have to somehow break the feedback loop.
A high resistance ground connection can also cause this.
Last edited by Yoyizit; 04-12-2009 at 02:27 PM.