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Old 02-28-2017, 02:17 PM
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Default DIY troubleshooting, now stumped
Model Number: MEDC300XW1   Brand: Maytag   Age: More than 10 years   

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Hi all,

I just found this forum as I'm attempting my first dryer repair. I have a basic background in electronics and electrical systems.

My dryer won't start. This happened suddenly without any warning.

Following the advice of various websites, I've performed continuity, resistance, and power checks on a number of components in my dryer. (I've attached the dryer's schematic for reference. It's an electrical heater.)

Everything shows good so far including;
  • thermal fuses - good continuity
  • thermostats - good continuity at room temp.
  • start switch & solenoid - good continuity & solenoid activation
  • timer assembly - timer motor runs when in a cycle
  • door switch - good continuity
  • motor - zero ohms across windings (start & run in parallel since motor hasn't turned.)

Of course, I've isolated each component by disconnecting a wire before testing.

When I close the door switch, set the timer to an active cycle, and press the start button, I hear the start solenoid engage and timer motor tick. Also, the motor power (LBU) reads 120v to the neutral cabinet. Releasing any of the switches disengages the solenoid.

Interestingly, voltage between the motor's two power lines (LBU/WHT) is all over the place, ranging from 5v when timer is off to no more than 42v when all switches closed and solenoid engaged. Voltages also vary when the timer is set to different cycles.

I'm suspecting the electronic control module at this point.

Any thoughts? I'm trying to avoid ordering parts that I just have to return (or can't return) later.

Thanks for any expertise.

Michael


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File Type: pdf Maytag MEDC300XW1 schematic.pdf (937.0 KB, 1 views)
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  #2 (permalink)  
Old 02-28-2017, 06:21 PM
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I'd verify that your starter relay is closing and staying closed when the button is pushed, it should not open unless the door is opened or the machine is otherwise stopped. It is a true relay, not a momentary switch like other machines have. These fail often enough that I carry one on my truck.

Do you have 120 at both ends of thermal fuse (or 0 potential across it) when the machine is trying to run? This is by far the most common reason a dryer will not run.

After that your timer could be losing the neutral (dropping it we'd say).

The elec control handles moisture sensing, I'd ignore it unless you have other reasons to suspect it, such as blatantly burnt resistors.
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Old 02-28-2017, 08:16 PM
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Thanks for the notes, Drew.

Yep, the solenoid stays closed and releases as I release any of the switches.

I've not tried a voltage test of the fuses under load. I suppose they might respond differently when passing a larger current than a meter produces.

What effect would the failed timer have when dropping neutral? Would the solenoid engage?

Thanks, again!

Michael
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Old 02-28-2017, 09:14 PM
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I find that most diagnosis is far simpler than it seems and I tend to go with what 10+ years of mistakes has taught me. It's difficult to convey how I operate and I've become over-confident with live work over the years. I don't want to lead you into a process that could harm you.

Neutral and hot meet at that start relay and I've changed many. This site allows returns I think so you might order start switch and timer and hope. You can test that live with little risk. When it is operating normally (or should be ) there is 0VAC potential between light blues. Meaning that there is no voltage difference(potential) between those terminals and therefore they are electrically connected. So with your meter on AC voltage you should see 0.

The motor would need 120v hot to neutral to run, so if the timer is not providing a good neutral you'd have trouble getting the motor to start. If you're seeing voltage #s like 45v something is odd, maybe a burnt contact in the timer or start switch.
You should still get a reading on the motor windings even unplugged at standstill. In the lower corner of that diagram is the motor plug layout. You can check the start and run windings using the #s indicated. The winding resistance is fixed, regardless of motor status. The only thing that changes during run is that the centrifugal switch closes and supplies 120 to the element, completing the 240v needed there to heat.

One thing that we've all missed at some point was a flipped breaker, bad cord, or bad outlet. It's worth verifying that the machine is receiving 240 or close to it at the terminal block. I've seen plenty of bad terminal blocks after hours of frustrating diagnosis.

There are very few reasons a machine will not start, Bad timer, bad start switch or relay, insufficient power supply, and thermal fuse are the main ones. Thermal fuse is 75% of the issues. You may have one of the 1% of odd ones.
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Old 04-09-2017, 03:54 PM
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Okay. I returned to this repair, today, after ordering a motor and control switch. I a/b tested both and no joy.

Next, I taped the door switch in the door-closed position, chose an active setting on the timer switch, and hit the start button. Solenoid closes and no motor.

I read full line voltage down the entire fuse and thermostat chain.

I tried various rotations of the timer, releasing and re-engaging the solenoid. No motor.

BUT...

At one point, the motor fired up for three seconds then stopped with the buzzer sounding, just like a short fluff cycle that runs after the dryer has finished its main cycle. (I believe the timer switch was in the "wrinkle prevent" section of the cycle.)


Next, I left the timer switch running for an entire "sensor dry" cycle to see if the "wrinkle prevent" feature would start the motor again. And, it did. The motor won't run during the regular cycle but the "wrinkle prevent" cycle activates the motor multiple times for around five seconds each time.

So, as I understand, the following items are operational:
  • door switch
  • start button & solenoid
  • all thermal fuses & thermostats
  • motor

Still suspect are;
  • timer switch (which I a/b tested)
  • electronic control module
  • temperature selector

What's left? Is there any failure of the heater that would prevent the motor from starting? (I note the "wrinkle prevent" cycle runs, which doesn't engage the heater.)

Thanks for any advice.

Michael

Last edited by mmorlan62 : 04-09-2017 at 05:17 PM.
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Old 04-09-2017, 08:34 PM
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You have a fun one! Only runs during wrinkle prevent...

If I was called to your house I'd get you a timer with fingers crossed. I still say ignore the moisture sensor board, as I rarely see them fail. The fact that it runs at all means the thermal fuse is good.

If you are comfortable with working on a live circuit you can pull the drum out and reconnect the front panel off to the side so the door switch is connected. Most of the live stuff is behind the bulkhead in this dryer. There's just the motor in front. Still use nonconductive gloves and eye protection in case of a surprise... I've both welded and vaporized meter leads over the years. As a general rule we don't work live unless there's no other way and I don't like even advising you to.

There are several 120v lines at the motor connector, a neutral, and a ground. When it should be running you should see close to 0v or 120v between any 2 terminals in the plug, my guess is you'll find an odd # when you test to neutral at the motor connector. We know the motor did not fix it so it's between the timer and the motor. If wrinkle prevent works you can use that to ID where you should be seeing 120v on other cycles. While you're there inspect the actual motor terminals on the wire harness for corrosion or burns.

If you have an air dry setting use it. If something changes and the motor runs on a heat cycle it will also be supplying the other 120v to the element and you can't let it heat for long while open like that.

They're dumb machines and quite simple so I am annoyed when I don't quickly find the issue. In this case process of elimination and experience says timer but doing 30-45 calls a week I am bound to be wrong once in awhile, also just part of the job.

Good luck, I'd like to hear what you find.
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Old 04-10-2017, 10:27 AM
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Hi Drew,

Yeppers. It's a beast. I've already performed live voltage tests on all the fuses and thermostats with the timer switch in a cycle. I certainly have no problem around line voltage. I have juiced movie sets in my other career. ;-) I had originally tested the motor connector without it connected to the motor and did receive some odd voltages. I'll return to that next.

I swapped out the timer for a new part without any success. (Wouldn't it be funny if it was a multi-layered problem?)

Michael
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