FIXED MED7000AW0 Maytag dryer has no heat

[davidgut]

Model Number

MED7000AW0

Brand

Maytag

Age

6-10 years

Hi, I have a Maytag MED7000AW0 that is not producing any heat. The dryer spins and everything else appear to work normally.
Using the diagnostic mode, I get an error of F4E4, and sometimes when running a load a see an error of L2 flash on the display.

Here's what I've checked so far:
- verified the power at the back of the machine, showing 120v from neutral (white) to L1 (black) and L2 (red). I also verified 240v from L1 to L2.
- tested and replaced the outlet thermistor and the heating element. Later I discovered my multimeter was giving me bad resistance readings, so those were actually fine.
- tested the centrifugal switch. There is continuity on the outside pins (the heater circuit) when the switch is activated.
- tested the inlet high limit cutoff, thermal cutoff and thermistor. The first two have continuity and the last one shows reasonable resistance measurements even when heated with a blow dryer.
- manually activated the heater circuit and got heat. I used a piece of wood to activate the centrifugal switch, then a short length of wire to simulate the heater relay closing, then turned on the breaker.
- tested the relay while the dryer is running. The relay frequently clicks on, but then clicks off again after 30s or so. I observed this intermittent switching several times.
- tested the relay itself using a 12v dc power supply. The relay consistently closed when I applied power, and opened when I removed it.

The only conclusion I can come to is that the control board itself is bad. Is there any other possibility? Based on my read of the schematic, problems anywhere else would also cause the motor to stop spinning.

 

[Jake]

Hi,

F4E4 L2 Line Voltage Error

L2 indicates low L2 voltage (less than 30 V) is detected at the CCU.

On your model it's common for the machine control electronics to fail. Unplug the machine. Remove the top panel and locate the machine control electronics on the left side. Take the control board out then remove it from the bracket and then turn it over. There's usually a burn mark on the board by the heater relay when it fails. If there's a burn mark, it's bad. If there is no burn mark that doesn't necessarily mean it's good so reinstall it and restore power to the machine. Measure the voltage between the black wire on the heater relay and P8-3 (white wire). Your meter should indicate 120 VAC. Then start the machine on timed dry, high heat and measure the voltage between the red wire on the heater relay and P8-3. Your meter should indicate 120 VAC.
(click to enlarge)


Here's the control board for your model:
WPW10542001 Electronic Control Board


Jake

 

[davidgut]

Thanks Jake, there's definitely no burn mark on the board, and it doesn't show any signs of damage that I can see. I also looked with a magnifying glass and didn't see signs of solder joints failing.
I'll reassemble the machine and try out the other measurements within the next couple of days.

 

[Jake]

Ok David, sounds good, keep us posted.

Jake

 

[davidgut]

Ok, I assembled everything and did the tests. I got 120v between the black wire of the heater relay. Then I wasn't sure how to measure directly at P8-3 while the machine was running, since P8 needs to be connected. Instead I measured between the red wire going into the heater relay and the white wire at the back of the machine. According to the schematic this should be equivalent to P8-3. It also has 120v. And I measured 240v between the red and black wires of the heater relay.

This seems like more confirmation that the heater circuit is working?

 

[Jake]

You can run the machine while testing at the control board David, that's the only way to find out which part is the problem child.

Jake

 

[davidgut]

Do you mean leave the board unmounted but everything else connected, and test at the back of the board? Will that be different than the test that I did to neutral wire at the back of the machine?

 

[Jake]

You test from the front of the main control board, see the diagram I posted above where the connectors are labeled?

You only needed to flip the board over to look for any burnt spots on it, not for voltage testing.

Jake

 

[davidgut]

I see, I figured out how to measure P8-3 while P8 was plugged in. I'm reading 120v across P8-3 and the red wire from the heater relay as well.

 

[Jake]

Measure the voltage between the black wire on the heater relay and P8-3 (white wire). Your meter should indicate 120 VAC.

--->Then start the machine on timed dry, high heat and measure the voltage between the red wire on the heater relay and P8-3. Your meter should indicate 120 VAC.

Jake

 

[davidgut]

Yes, that is what I checked
machine off, black wire at heater relay to white wire at P8-3: 120v
machine on timed dry, high heat, red write on heater relay to white wire at P8-3: 120v

 

[Jake]

Then it must be heating right?

Put your meter probes on each of the heating element terminals and see if you are getting 240 volts when the dryer is running on timed dry, high heat.

Jake

 

[davidgut]

Yes, at the moment I have heat and no L2 errors. The problem has always been intermittent. It seems to be better right after I've reassembled the machine and worse when my wife is trying to dry a load of laundry. Also don't these checks leave out the heater relay? I've observed the heater relay clicking on and off, even when the dryer isn't up to full temperature. As long as the heating circuit is good, red at the heater relay to white at P8-3 should always read 120v when the machine is on, regardless of what the heater relay is doing. Same goes for black to white.

Any recommendations on how to get access to the heating element terminals while the machine is running? I supposed to would need to short the door switch so I can leave the front panel off, then clip my meter probes onto the heating element terminals?

 

[Jake]

I forgot this was a intermittent problem, well my friend intermittent issues are always the hardest to nail down till it quits heating altogether. So I don't know what else to suggest until it quits heating period!

Don't worry about taking the volt reading at the heating element terminals now.

Jake

 

[davidgut]

I managed to get the dryer to heat and also fail to heat while I was taking some measurements. Whether the dryer is heating or not, when it's running I get 120v between red at the relay and P8-3 However I found that I'm getting very different readings at the back of the machine. When it's not heating, I'm showing 0 volts from red to black. When it heats, I have 240v. So it seems like this is pointing to an electrical problem after all.

 

[Jake]

When it's not heating, I'm showing 0 volts from red to black. When it heats, I have 240v. So it seems like this is pointing to an electrical problem after all.

Yes, that is definity a electrical problem in home breaker box.

Good find.

Jake