DV218AEB Samsung Dryer Keeps Blowing Thermal Fuse

justmore

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Model Number
DV218AEB
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Age
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Have a Samsung dryer that's a few years old, Model No. DV218AEB.

The dryer no longer heated up two days ago, so I took the dryer apart and checked for blockages, tested everything with a multimeter for continuity and shorts, and found the thermostat cut-off had blown. Everything else tested within spec and there were no shorts or any visually obvious issues.

Replaced the thermostat cut-off with a new one (Samsung Part No. DC47-00016A) and put it back together. Dryer heated up fine the first time it was turned on and run for a minute, but then apparently blew the thermal cut-off immediately the second time it was turned on, since it no longer blew hot air again.

I took the dryer apart again and replaced the high-limit thermostat (Samsung Part No. DC47-00018A) at the heating element even though the original tested good. Put the dryer back together, again, worked fine when turned on and run the first time, heated properly, but blew cool air the second time I turned it on.

Just throwing this out there to get any ideas on what to check or personal experiences on what causes dryers to blow thermal cut-offs like this so I don't keep throwing parts at it.

There is NO blockage anywhere, dryer is extremely clean and there was no lint buildup at all, the vent system goes straight out an unrestricted 4-inch pipe.

Thanks in advance for any helpful replies.
 
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jeff1

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justmore

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Thanks for the reply.

Just a guess, element shorted to ground?
I checked the heating element for a short to the housing (or the metal plate it's mounted to) as one of the first steps, using a multimeter and checking each end of the coil.

I've taken apart the element assembly to inspect it visually, the element looks great, has the correct ~10 ohms reading at room temp, and is not touching the housing or any other metal when assembled (verified again with multimeter).


Also checked a lot of other things - the thermistor reads the correct ~10K ohms at room temp, and goes to ~7K ohms when warmed and about ~15K ohms when cool. The second thermostat cut-off (right after the blower, next to the thermistor) has not blown and shows continuity.

The motor runs fine and is getting 120V, and the heater relay seems to be working and getting 240V since the element heats up, at least once the dryer is first started up after replacing the thermal cut-off. I've even checked the centrifugal switch at the motor, and while it doesn't read as the exact 2.88 ohms between pin 3 and 4 or the 3.5 ohms between pin 4 and 5 that the troubleshooting manual calls for, it does read at least 2.5 ohms and goes close to 2.8/3.2 so I'm pretty sure the switch isn't causing it either.

There are no error displays or diagnostic codes. Test mode doesn't reveal anything since the dryer runs fine otherwise, just has blown two thermal cut-offs with no obvious cause.

At this point I'm guessing it's the main PCB (Samsung Part No. DC92-00160A) since there's nothing else I can come up with based on the troubleshooting I've done so far. Sure don't want to spend the $$$ only to find out it's not the PCB though.



What about the normal on and off heats, checked them to see what the temp is cycling the element on and off?
Not sure what "the normal on and off heats" means here.

There is no cycling of the element on and off - the thermal cut-off just blows the second time the dryer is run and so there is no heat.

Should I bypass the cut-off and check to see what temps the element gets up to with a non-contact thermometer or something like that?

Maybe I should have let the dryer run longer with the new thermal cut-off to see if it would overheat and/or blow the thermal cut-off like that, but it seemed fine, only seems to blow the cut-off the second time the dryer is run.
 

jeff1

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Not sure what "the normal on and off heats" means here.
That is what happens normally....dryer heats up ( EG: 150ºF ) and the heat cycles off, dryer cools to ( EG:110ºF ) and the heat comes back on....getting an idea what is happening ( getting way too hot, not cycling off, etc ) can help as to why the thermal/high limit keeps opening up.
Vent off, test with no clothes inside and a thermometer at the dryers exit...record the temps.

jeff.
 

jeff1

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Good.

jeff.
 

justmore

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Ok, checked the heat cycling with both a 200*F meat thermometer at the exhaust vent and a non-contact infrared thermometer. The meat thermometer seemed pretty dang accurate, even more so than the infrared, which showed about 10-15 degrees less than the meat thermometer, even when held very close to the vent and pointed at the inside walls. Guess they really aren't so great for checking air temperature.

Did the first run on "normal" cycle (which seems to use the moisture sensor) it went up to ~140-150*F on the meat thermometer and stayed there, showed slightly less on the infrared. The dryer stopped automatically on it's own after about 2-3 minutes.

Did the second run right after, on the "timed dry" cycle, with highest heat setting selected. It took a minute to get up to 140*F, then climbed to 150*F after another minute, then slowly went to 160*F, then 170*F, and backed off, taking only 10-20 seconds to go all the way back down to 140*F, where it held for another 10-20 seconds, then slowly climbed to 150*F again, then 160*, and finally 170*F, where it stayed for a 10-20 seconds, then backed off again all the way to 140*F.

So, two complete cycles getting up to 140*F, going all the way to 170*F, and back down to 140*F.

I guess this means the thermal cycling is okay and the cut-off isn't blowing because of high heating element temps.

What else blows a thermal cut-off?
 

jeff1

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It is good that it is cycling the heat off, cooling down and cycling the heat back on....but 170ºF is a bit too hot to me....160-165ºF might be better....has any body cleaned off the thermistor facing to make sure no dryer sheet gunk or such is built up on the sensor facing?

What else blows a thermal cut-off?
Thermal is heat, that is what trips it...maybe amps can do that is a loose connection caused the voltage to drop and the amps to increase to compensate.

jeff.
 

justmore

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It is good that it is cycling the heat off, cooling down and cycling the heat back on....but 170ºF is a bit too hot to me....160-165ºF might be better....has any body cleaned off the thermistor facing to make sure no dryer sheet gunk or such is built up on the sensor facing?
I don't know for sure that the temp was EXACTLY 170*F, it may have actually been 165*F but the analog thermo just went to about the 170*F mark before dropping. The high limit thermostat I used was the brand new one I just bought, an OE Samsung replacement.

The thermistor was cleaned off gently with some water, I was wary of using electronic cleaner or anything else since I didn't want to damage the protective coating on the sensor that it seems is critical.

Maybe replacing the thermistor makes the most sense at this point if the temps are just slightly high.


Thermal is heat, that is what trips it...maybe amps can do that is a loose connection caused the voltage to drop and the amps to increase to compensate.
I realize how it's supposed to work, but it appears that heat isn't what has tripped it, since the replacement thermal cut-offs have blown -twice- before the dryer even gets warm on the second test run after replacing it.



Is a thermal cut-off supposed to be "broken in" somehow or brought up to temp and cycled a few times in the initial run?

If there's nothing else wrong with the dryer, and there are no shorts, but the thermal cut-off just blows after being installed, I'm guessing it's user error and I'm doing something wrong or not doing something else that I should be doing before running the dryer.

Either that or I've managed to get defective thermal cut-offs.
 

justmore

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Ok, I have figured some stuff out. This is starting to make sense. Finally.

The replacement thermal cut-off, DC47-00016A is the WRONG PART.

Yes, this is the part spec'd by Samsung to be the high limit thermal cut-off, but it is WRONG.

The original part I removed was a CS-7 B-2 K160 thermal cut off, which is spec'd to cut off at 160*F.

The replacement DC47-00016A is actually a PC-17/PC-17S B-2 K85 thermal cut-off, which is spec'd to cut off at 85*F.

Obviously what's been happening is the 85 degree thermal cut-offs simply cut off because they hit the thermal limit even though the dryer is just at normal temps that wouldn't blow the 160 degree cut offs.

I've also learned the trick of smacking a thermal cut-off to reset it. Not sure if a smacked reset one is as safe as a new one, but there's continuity so I can use it instead of a jumper in the meantime.

I'm guessing since the high end of the cycling temps are 170*F that I need a new thermistor and that was the original cause of the blown 160*F thermal cut-off.
 
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jeff1

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jeff1

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The thermistor is a fairly cheap part, not a terrible idea to change it out at the same time.

jeff.
 

JBROSS

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I am having a similar problem on my Samsung DV350aew/xaa. I have had two heater coils fail and have blown 2 thermal fuses (on the heater housing) part DC47-00015A. I have replaced the main control board and the thermistor (part DC32-0007A). When I mointor the voltage to the heater at the control board, its stays at approximately 120 VAC the entire cycle. What else could be keeping the heater on for the whole cycle? The heater coil is not shorted to ground. The voltage to the heater is zero when I power on the dryer and goes to 120VAC when I start the cycle and stays there. Also, what is the difference in the two thermostats in the heater circuit? One is called the "thermal cut off" and the manual shows it is 160 degC (this is the one that keeps blowing) and the other is the "Hi-limit" and is 127/99 deg C which appears to reset. I thought the thermistor and control board would cycle the heat to the heater, but is the HI-limit thermostat what should be cycling the power to the heaters? It is the only thing I haven't replaced.
 
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jeff1

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Hi,

DC32-0007A
Comes up as nothing for me.
I got DC32-00007A to work for me.

When I mointor the voltage to the heater at the control board, its stays at approximately 120 VAC the entire cycle
From what to what? Not to ground/cabinet I hope. The element is 220-240 volts, if it is not getting that it is not on.

I thought the thermistor and control board would cycle the heat to the heater
During normal operation yes, the thermistor changes resistance and this tells the board to cycle the heat on or off during the normal drying process.
The safety or high limit thermostat or the thermal fuses will only trip when there is an issue of some sort.

I have had two heater coils fail and have blown 2 thermal fuses
Check venting ( all the way from the dryer to the outside and the vent hood ), check ducts inside the dryer, check fan blower wheel, check lint filter.

blown 2 thermal fuses (on the heater housing) part DC47-00015A.
That isn't the right one...

Thermal-Fuse-DC96-00887A-01647062.jpg LINK> Thermal fuse with bracket

jeff.
 
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JBROSS

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One leg of the 240VAC comes into the board and goes through a relay contact and back out to the heater. I assumed this relay contact is what is cycling on and off the heater. I was measuring from there to cabinet ground to get the 120, but the heater does have 240 on it. If the contact opens, I should have zero volts.

So, I have replaced the board and the thermistor. I removed the duct from the back of the dryer and ran it. I measured the temp going up to around 170 degrees then it dropped to about 140 degrees, then back to 170. I probably wasn't giving it enough time when I was checking the voltage at the relay on the board to see it the contact opened because I only waited about 3 minutes. When I was checking the temp on the exhaust, it took about five minutes to cycle the first time, i.e. reach 170. I thought it was working but a blew another fuse after about 3 loads.

The thermal fuse I listed is the correct one. The part number you gave is for the same fuse, just with the bracket attached. I only ordered the fuse by itself.

I have taken the dryer apart. There is no lint buildup anywhere. Everything looks good. The only thing I noticed was when I tested the dryer exhaust and it appeared to be cycling, I was using the timed dry setting. When the fuse blew, I was using one of the normal dryer settings (perm press). Not sure if that could make a difference. Any thoughts?
 

jeff1

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I was measuring from there to cabinet ground to get the 120
Shouldn't, can easily confuse when testing to ground or the frame.

I measured the temp going up to around 170 degrees then it dropped to about 140 degrees, then back to 170.
At the exit of the dryer? Those are a little high to me. 110-160 or 120-165 would have been more normal to what we see with no clothes in the dryer.

The thermal fuse I listed is the correct one
The ones without a broacket are often an incorrect temp...I hope it is right, are the temps listed on it the same as the one o nthe bracket??

jeff.
 

JBROSS

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The temperature I'm measuring is at the dryer exit, with a meat thermometer. Not sure how accurate it is. I am only using the voltage I'm measuring as a way to see if the contact on the heater relay is opening. Shouldn't this contact open up to cycle the heater on/off during the cycle? The voltage on the heater side of the contact would go to zero if the relay contact opens, but I'm seeing the temperature cycle and this contact never opens. The only other way I can see the heater cycling on/off is with the HI-LIMIT thermostat on the heater housing. Per the manual, it trips at 127 deg C and resets at 99 deg C. If the board isn't cycling the heater on/off, would this thermostat by cycling the heater? Of course, if this thermostat is cycling the heater, why would the thermal fuse blow (setting of 160 deg C)? And the thermal fuse I installed does have the correct temp on it (160).
 

JBROSS

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I just realized I will get 120 to ground on the load side of the contact regardless of whether the contact is open or closed. So, I measured voltage across the contact and the voltage was essentially zero the entire time, meaning the contact was closed (I should get 240 volts when the contact opens). I did this with the dryer set to time dry, high heat. Thus, the HI LIMIT thermostat was opening the circuit and cycling the heater on/off. I changed to low heat and tried again. This time, I saw the voltage across the relay contact go from zero to 240 after a couple of minutes, meaning the contact was opening like it should. I then tried medium heat and then high heat again and it worked like it should this time. I would think it was a sticky relay on the board except this has happened with two separate boards.
 
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