MDE2400AYW Dryer only producing low heat

FrakeTrain

Premium Member
Joined
Apr 15, 2019
Messages
8
Location
Colorado
Model
MDE2400AYW
Brand
Maytag
Age
6-10 years
Hello. I've attempted all troubleshooting techniques that I am capable. Please make any suggestions you may have. No other forums have provided any viable suggestions...

Dryer: Maytag MDE2400AYW

Problem: Dryer producing very little heat.
Assumptions: Problem with Resetable Thermal fuse (sensor), High Limit Thermostat (sensor), Thermistor (sensor), or Heating element.

Troubleshooting steps:
Took top off unit so I could see the element condition while running. Turned unit on and I could feel low heat, but the element was not glowing red. I then removed the element from the unit and placed on the floor and connected back to harness. Turned on unit and element glowed full red. I then checked for continuity, resistance, and ground short (element housing continuity with element). All looked ok. So then moved on to other items.

Placed element back in unit. I then removed both the Resetable Thermal fuse and High Limit Thermostat from the back of the element housing cover (but kept the wires connected) and placed off to the side. Turned unit on, same low heat issue. Then I pulled the wires from both of these 'sensors' and hard wired the harnesses together to completely remove them from the schematic (totally closed circuit). Turned unit on, same issue. Checked both sensors for continuity, both ok.

Ok, got to be the Thermistor. I then removed the Thermistor from the fan duct. Kept the wires connected, pulled Thermistor outside unit, placed inside towel to isolate from any temperature changes. Turned unit on, SAME ISSUE. So not a sensor problem. I checked the Thermistor resistance at 68 degrees and matched exactly the service manual (60K Ohm) and then changed ambient temperature while testing resistance and thermistor reacted accordingly.

Ok here's the kicker...
Now, the element is installed, the two thermostats (sensors) are disconnected and their harnesses hard-wired together, and the thermistor is connected but outside the unit inside a towel. I then remove the lint filter, check for any obstructions in the blower and tape the door switch closed. I open the door to 90 degrees. I turn the unit on... and WHOA, full red glow form the element. I then start closing the door and when it gets to about 1" from shutting, the element starts to decrease in glow. At door fully closed, the element goes back to no red glow, but producing low heat. I have removed all the sensors from the electrical equation and element is still reacting to something.

Now, time to take out the service manual and check for codes and resistances through the board. No codes show up, and all the diagnostic steps and resistance tests through the board show anything wrong. I even tested the voltage across the element while the door was moving to turn the element from red to low heat and the voltage remained at 240V.

Is it possible that air blowing past a "weak" element is causing it to cool off? Or is there some other sensor that I am missing and is not on the schematic that is reacting when outside air starts to be pulled through the element and then warm air from the glowing element through the unit blower. The blower seems to be working perfect and the drum is turning as always.

I have attached the last page of the service manual for the Schematic.

Please any suggestions are worth trying at this point. The dryer is pretty old and the element is one of those self contained pricey units (over $100) so not worth replacing to troubleshoot (and by itself, it seems to be able to produce full heat)


Thanks in advance
 

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jeff1

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Hi,

1) Stop thinking the glowing of the element will help you out.

Good or better air flow past the element will draw the heat out of the element = less glowing....open the door and we loose air flow across the element and it will glow brighter red, which does not mean the dryer will get hotter.

Problem: Dryer producing very little heat.
2) No clothes inside, measure the heat temps cycling on and off with the vent attached to the dryer. Observe for a min of 30 minutes.
3) No clothes inside, measure the heat temps cycling on and off with the vent off of the dryer. Observe for a min of 30 minutes.
Write these down and post the results here.

jeff.
 

FrakeTrain

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Apr 15, 2019
Messages
8
Location
Colorado
Thanks for the reply,

1) Just wanted to make sure the element was operating and take a visual on that. Definitely realize air will draw heat out of the element, just was surprised that it drew that much out to completely eliminate glow. I am curious to know how the heat in those units are regulating production. Is the control board sensing increased heat from the Thermistor (when the clothes are getting dryer) and then using a variable voltage regulator to lower voltage to the element thus producing less power (P=V2/R) or since this particular element is connected to each leg of the 240V, does it just have full 240V or half 120V power production? Or are they just cycling electricity to the element to regulate heat production?

2) This old dryer has never had a vent to the outside and thus no vent except for the interior to one of the those floor vent boxes that hold water to eliminate lint. Yes I know that is a horrible way to dry clothes, drying humidified air, but this is not my dryer and trying to help a friend out. This dryer has performed this way for years. So I can only measure temps with the interior vent attached, aka no vent. And how should I measure temperature? Should I be placing a thermometer (what type of thermometer?) at the end of the exhaust at the back of the unit? And when you say cycling, are you saying that these dryers cycle the element on and off and how am I able to tell if the dryer is cycling? By measuring the voltage across the element while operating? And when you say "Observe for a min of 30 minutes" do you mean take a temperature measurement every minute for 30 minutes?

In order to help me help you troubleshoot, please let me know what you are trying to see from this procedure? I am fairly confident that the air temp will remain the same, but I will try. And MOSTLY do you want me to keep the 2 Thermostats disconnected (hardwired together) and the Thermistor connected but removed from the blower duct and placed in towel outside unit while I try this procedure? (This is the existing condition of the unit when I did the door trick).

Thanks again
 

jeff1

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Should I be placing a thermometer (what type of thermometer?) at the end of the exhaust at the back of the unit?
Yes.

how am I able to tell if the dryer is cycling?
You will see an increase and decrease in the temps. EG: Heat on at 100ºF and the heat shuts off at 150ºF....cool down from 150ºF to 100º and the heat comes back on, etc etc.

do you want me to keep the 2 Thermostats disconnected (hardwired together)
Wouldn't tell us much if the dryer wasn't in it's "normal" position.

Or are they just cycling electricity to the element to regulate heat production?
Correct.

jeff.
 

FrakeTrain

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Messages
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Location
Colorado
Finally got to my friends house to test...

First did the temperature test with all the sensors (Thermostats and Thermistor) OUT of the equation as noted above in order to establish a max temp. Took temperature readings every 60 sec on Automatic High Heat cycle at back of dryer vent, no venting attached:

1) Temperature at 1 min = 95 deg F. Then temp gradually climbs every minute until at about 20 minutes where stabilizes at 153 deg F and stays there. No heat cycling was evident as I can hear the "click" of the power cycling, and there were no clicks and no decreases in temp.


Then hooked up the Thermostats and the Thermistor and tried again on Automatic High Heat Cycle (Thermistor engaged, but no clothes so auto shut off):

2) Temperature at 1 min = 114 deg F. Then climbed to 130 deg F at 4 min. Then decreased to 104 deg F at 5 min, then powered off.


Then tried again on 1 hour Timed High Heat Cycle (Thermistor engaged, but no auto shut off until time is up):

3). Temperature at 1 min = 112 deg F. Then climbed to 124 deg F at 4 min, then power cycled ("clicks") and temp decreased to 106 deg F. This power cycle continued every 30 sec. From 106 to 124 in 30 sec, then 124 to 106 in 30 sec until time was up.


SO, without clothes (dry clothes) in the dryer the average temperature is approx 115 deg F on Timed High Heat cycle (this seems very low). I'm guessing I should try with wet clothes in the dryer to see how the Thermistor reacts to cooler temps due to evaporation?

My big question to help me solve this is what are "normal expected temps" for electric dryers at exhaust with wet clothes and without clothes (dry clothes)??

Thank you for your help.
 

jeff1

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Venting attached or removed from the dryer?

I'm guessing I should try with wet clothes
Nope.

what are "normal expected temps" for electric dryers at exhaust
With out clothing, heat on 100-120ºF.....heat off at 140-160ºF.

Temperature at 1 min = 95 deg F. Then temp gradually climbs every minute until at about 20 minutes where stabilizes at 153 deg F and stays there.
Sounds like poor air flow ( could be venting, ducts inside the dryer ) or something leaking ( fan blower seal, drum seal ).

jeff.
 

FrakeTrain

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Messages
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Location
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Venting attached or removed from the dryer?
No venting attached on any of these tests. Temperature probe positioned at center of exhaust vent at back of dryer.

When I say "Temperature at 1 min = 95 deg F. Then temp gradually climbs every minute until at about 20 minutes where stabilizes at 153 deg F and stays there." Remember this was to test the heat output of the element without the influence of the sensors (In this test #1, the Thermistor was connected at the harness, but placed outside the dryer in a towel. The two Thermostat harnesses were taken off the leads and wired together to force a closed circuit and remove the influence of the Thermostats.)

For this test #1, do you say: "Sounds like poor air flow ( could be venting, ducts inside the dryer ) or something leaking ( fan blower seal, drum seal )." because you think the dryer should have reached 150's deg F sooner? (I have checked all the ducts inside the dryer except for taking apart the blower and the blower exhaust seems to have good flow. And at least I know it can reach into the 150's, so probably not the element)

Now, I have some 101 dryer questions to help further this. I have done two tests #2 and #3 with all the sensors connected. I need to know how the Thermistor is functioning.

1) Is the Thermistor only involved in "AUTO" settings? (AKA higher temperature at the blower means dryer clothes and less evaporation, so auto shut off?)

2) There are two Thermostats connected in series on this dryer, a high heat shutoff with a reset button, and another that I presume closes at a low temp and opens at a high temp. When I choose a "TIMED" setting, is the high/low Thermostat controlling the heat cycling? And if so is it possible that the Thermostat is failing and opening and closing at lower than spec temperatures? Is it typical for one of these Thermostats to fail in this manner?

Please continue, these tests have given me much insight and I feel I am close now to solve. Thanks again
 

jeff1

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When I say "Temperature at 1 min = 95 deg F. Then temp gradually climbs every minute until at about 20 minutes where stabilizes at 153 deg F and stays there."
Temp should go up a lot fast...a minute or two or three.

because you think the dryer should have reached 150's deg F sooner?
20 min is way too long.

And at least I know it can reach into the 150's, so probably not the element)
Has the element been checked for being shorted to ground?

Is the Thermistor only involved in "AUTO" settings?
No.

When I choose a "TIMED" setting, is the high/low Thermostat controlling the heat cycling?
Thermistor does.
Safety thermostats ( ones in series ) only do something to protect the dryer and such if someone forgets to clean the filter, etc.

jeff.
 

FrakeTrain

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Has the element been checked for being shorted to ground?
Yes, I checked continuity of the element metal housing with the power leads when the element was disconnected and removed from the dryer. Curiosity, what would be the symptoms of this?

Another eliminating question:
Is it possible for these elements to substantially increase in resistance as they get older, thus producing less heat (I've never heard of this)?

Now, with my Test #1 (all sensors removed from the equation) and you say that the temp at the exhaust should be raising much faster, so I understand why you suggest a clogged system or cold air contaminating the heated air through a drum leak, blower gasket leak or door gasket leak. If it were a clogged system, then I would expect to see a little more glow from that element as less air is passing through the element, and low air flow at the back exhaust. Or if cold air contamination, this would also produce less air flow across the element, but would keep the flow at the back exhaust the same or higher. I will test for these things through various methods after I try a few more tests on the sensors.

You say that the Thermistor regulates all the power cycles to the element and that the two thermostats are safety devices only. As you probably already know, according to the service manual, there is one resettable Thermal Fuse set to go off at 293℉ and a High Limit Thermostat set to go off at 194℉ and on at 167℉ (I will keep everything in our discussion in ℉). These are wired in series and attached to the metal element housing. I will now do the same exhaust temperature tests, but isolating each of these sensors, and will get back with results, one question:
Is it possible that the Thermistor is failing, and even though it meets the resistance spec of 60K Ohm at 68℉, but is sending bad resistance values to the control board at higher than room temperature, thus lowering the element power cycling temps?
 

jeff1

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Curiosity, what would be the symptoms of this?
It can go either way. Sometimes the element stays on and we over heat or heat when we shouldn't be heating. Sometimes the thermal fuse will let go when this happens. Sometimes just a small section of the element will come on and we get low or poor heat.

Is it possible for these elements to substantially increase in resistance as they get older, thus producing less heat
Nope.

You say that the Thermistor regulates all the power cycles to the element
Nope.
The thermistor changes resistance, this is is picked up by an electronic device and changed into what the temp is in the drum/fan blower area. Something else turns the heat on or off, often a relay.

Is it possible that the Thermistor is failing, and even though it meets the resistance spec of 60K Ohm at 68℉, but is sending bad resistance values to the control board at higher than room temperature, thus lowering the element power cycling temps?
Definetly possible. Could fail cold, could fail once heated up.

jeff.
 

FrakeTrain

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The thermistor changes resistance, this is is picked up by an electronic device and changed into what the temp is in the drum/fan blower area. Something else turns the heat on or off, often a relay.
Yes, that is what I meant to say. I realize a thermistor is just a resistance type temperature probe that sends resistance values to an electronic control board that then translates those resistance values into temperature values, then cycles the power to the element through a relay. Since this dryer is spec'd at 150℉ on high heat, I am assuming that the Thermistor values should be cycling the element around 155℉ off and 145℉ on (exhaust temps) or something like that. Since I have already shown that this dryer is capable of 153℉ with no sensors, and that with sensors is cycling at much lower temperatures, I'm leaning toward the Thermistor, especially since you said that it can report the correct values when cold, but incorrect when warm.

I will do one more test to see if I can get the High Limit Thermostat to cycle (not the Thermal Fuse). So I will test the temperatures at exhaust with the Thermistor removed from the blower vent but still attached to the electrical harness and placed outside the dryer in a towel. I will also hardwire the Thermal Fuse harnesses together just in case it's doing something funky. If I can get the dryer to cycle at higher temperatures using the High Limit Thermostat, then I know it is the Thermistor. OR hopefully not, the control board reading the Thermistor incorrectly. That would suck as it is too expensive and I don't think available any longer...

Thanks again, might be awhile till I can get back there to test, but I'm getting much closer to solving.
 

jeff1

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Since I have already shown that this dryer is capable of 153℉ with no sensors
Didn't help much, should have been much higher with no controlling devices.

jeff.
 

FrakeTrain

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Greetings jeff,

Finally have some concluding results:

Thermistor removed from blower vent and placed in towel outside dryer. Thermal fuse disconnected and harnesses hardwired together. High Limit Thermostat connected and in place. Within 5 minutes the exhaust temp raised to 135℉ and at 10 min was at 150℉. I realize this is not as efficient as should be, but at this point I'm just trying to solve the previous diagnosed problem of the Thermistor cycling at low temps (120℉ off, 105℉ on). This test was just to see if the High Limit Thermostat would cycle, but it didn't after 20 min and the exhaust temp at 155℉. Now I realize, the top is off the dryer and the rear lower panel is removed, so there is much more cool air getting to the element.

I then order a new factory packaged thermistor on eBay. I install the new thermistor and try the exhaust heat test again. The new thermistor performs exactly as the old one: cycling at 120℉ off and 105℉ on. DAMN! Not the thermistor. The only thing that I can surmise is that my fears of the control board gone wacko on translating the thermistor's resistance values into actual true temperatures. I have been told that this board is not available any more, but even if it was, it is too expensive to revive this old unit. If you have any other suggestions of what may be keeping the cycling temperatures so low, your advice is welcome. ie. Is there a reset to these control boards that is not noted in the service manual?

What I have done finally to salvage any usability of this unit is to take the thermistor out of the blower vent, keep it connected to harness, place in ziplock baggie, and rest it on the back corner of the dryer floor. Install both thermostats for safety reasons and instruct the user to only use timed mode and try never to over-dry. I did one final exhaust temperature test with the unit completely assembled, and at 20 min the temp got to 168℉ and at 30 min, 176℉. The High Limit Thermostat (specifications: off at 194℉ and on at 167℉) still did not trip, but when I felt the area at the back of the element where the thermostat resides, it was cool enough to touch, but just downwind of the element was too hot too touch. So I'm guessing that the thermostat would get hot enough to trip if the unit got clogged up or the bower stopped working.

Thanks again jeff for the open source ability to enlighten ignorance and if you have any final thought please share.
 
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