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Replacement parts for KENMORE 41784072300 | AppliancePartsPros.com

Here is the wiring diagram
http://manuals.frigidaire.com/prodinfo_pdf/Webster/1342003e_sheet_1.pdf

First thing to check is that the unit si getting 240 volts.
Try flipping the breaker off/on slowly a couple times, sometimes you can loose half the line without actually tripping the breaker.
If this does nothing, check the voltage at the plug
L1 to L2 should be 240 volts
L1 to Neutral and L2 to Neutral, both should be 120 volts.
If OK
Unplug the unit and check the wires at the terminal strip in the machine to make sure none are loose or burned out
If OK
Check the power at the terminal strip.
[COLOR="Red"]Be careful as 240 volts is lethal !!! [/COLOR]

Then I would double check the hi-limit thermostat.
Be sure to disconnect one side of it to be sure you do not read an alternate/parallel circuit path.
It should be 0 ohms.

Then I would check the thermistor.

If you do not own a meter, I would suggest you purchase a one. You can get a decent digital multimeter for under $20.00. You do not need fancy though it is nice if the leads are a couple feet long.
If it saves ordering one unnecessary part it has paid for itself and you end up owning a useful tool.
Most places will not let you return electrical parts so if you order it, you own it.
A couple things to watch when measuring ohms and continuity
1. Always remove power from the machine otherwise you could blow your meter.
2. Always disconnect at least one side of any device you are checking. This eliminates the possibility of measuring an alternate/parallel circuit path.
3. When checking for closed contacts and continuity use the lowest scale (Usually 200 ohms). Then try higher scales. This scale is 0 to 200 ohms so if the device you are measuring is 300 ohms this scale would show an open circuit which it is not, you are just measuring outside the scale's dynamic range.

There is a good STICKY at the start of this forum about it's use.

But do you have 240 volts between L1 and L2.

The heater circuit (L1 to L2) is 240 volts so measuring with one meter lead on Neutral or earth ground (unit frame) does not really tell you much and can be confusing.
You cannot tell if you are measuring L1 or L2 voltage.

As an example if I assume that the heater relay is closed, the unit is running but I have no heat. Hi-limit and heating coil are good.
With one lead on Neutral, I will measure 120 volts on the L1 side at every component all the way to M1 on the centrifugal switch. I am measuring the L1 voltage.
If I then measure to M2 on the centrifugal switch, I will also see 120 as now I am measuring the L2 voltage.

Now if I take the meter lead off Neutral and place it on L1. I measure 0 volts all the way to M1. I also now see 240 at M2.
Now if I move my leads to M1 and M2, I see 240.

What the above is telling me is that the centrifugal switch is not closing because if it was there would be 0 volts across it.

I hope I explained the above in a way that makes sense.

Also I unplug the wire terminals from the heating element and had 120 volts on the M1 wire going to the element and 0 volts on Blk wire coming ouit of the heater relay.
I am assuming the above was with the unit running.
So the voltage at M1 would be L2 and it looks like the relay on the board is not closing.

If the control thermistor measures good then I think you need a new control board.