samsung dryer DV331AEWXAA01 popping high limit thermal fuse, running too hot?

Model Number: DV331AEWXAA01
Brand: Samsung
Age: 6-10 years

Greetings,
Looking for some ideas on this one if possible.
I have a samsung front loader dryer model number DV331AEWXAA01 that popped the thermal fuse. Verified the heater element was not shorted to the case and was not open, and verified the thermostat on the heater element case was not open. Verified the dryer vent hose was not blocked and had good exit air flow. Replaced the thermal fuse PN DC96-00887A, blew it again shortly after running the dryer. Then replaced the fuse again, replaced the thermostat PN DC47-00018A, and also replaced the heater element PN DC47-00019A even though I found no problem with the thermostat or element. I ran the dryer with the front cover off so I could watch the heater element cycle on and off, which it did, so it looks like the controls to cycle the heater element are working, but maybe not at the correct temperature? Reinstalled the front cover, popped the thermal fuse again after starting another load.
I tore down the dryer and removed the drum, front and rear drum seals look ok but not sure what worn ones would look like. I then removed the blower wheel for cleaning and verified the duct work from the blower to the rear of the dryer are clean and clear. Removed the thermistor from the blower wheel duct work, PN DC32-00007A, and measured 10200 ohms at room temperature. I then wiped it off in case there was lint on it, rechecked after that and read around 9500 ohms.
I think the dryer is running too hot but I am not sure why. I installed a jumper to jump out the high limit fuse for testing and the dryer just feels too hot. I have to get a temperature probe to check the dryer vent temperature, but I do have a new thermistor DC32-00007A on order.
Is there anywhere else I can look for an air blockage, like behind the rear cover? That is the only area I have not checked yet but since the dryer vent blows hard I and the blower wheel duct work is clear I figured there should be nothing back there. Any other seals to inspect? So far the ones I have touched look ok, drum seals, lint trap seals, front cover to bulkhead seal. Hoping there is a problem with the thermistor if this is used for cycling the heat on and off.

Can anyone tell me is the thermostat on the heater element enclosure the primary temperature control for cycling the heater element off and on? Is the part next to the thermistor on the blower wheel housing another overtemp thermal fuse? I have read that the thermostat on the heater housing is a high limit thermostat that should not normally be cycling open and closed, is this correct? If that is correct where is the primary heater element control?

Here is a link to the unit's fast track tech sheet
https://drive.google.com/drive/folde...XdidFJ6SHRPVzg

The thermostat on the heater is a hi-limit thermostat.
It is a safety device and under normal circumstances should not cycle.
But if for some reason the heater overheats it will cycle. It's contacts are not as robust as a heat control cycling thermostat so eventually they over heat and fail (usually welded closed)
Then the thermal fuse (cut-off) on the heater blows as it is the secondary safety device.
This cuts power off to the heater.

Yes the other device on the blower wheel is also a thermal fuse.
If it blows it cuts power to the motor which shuts the unit down.

The primary heater control device is the thermistor.
It's resistance is fed to the board and then the board controls a relay (on the board) to cycle the heater element.

Thank you,
While testing the dryer with the front cover off to watch the heater element cycle off and on I could hear a metallic "ping" sound as it cycled. I assume the relay on the control board is an SSR so there should be no noise when cycling. so possibly it is stuck closed and now using the safety relay to cycle the element. Now to find a PN and schematic for the board so I can check the relay, going through the google drive link you posted first.

Quote:

---

Originally Posted by denman

Here is a link to the unit's fast track tech sheet
https://drive.google.com/drive/folde...XdidFJ6SHRPVzg

The thermostat on the heater is a hi-limit thermostat.
It is a safety device and under normal circumstances should not cycle.
But if for some reason the heater overheats it will cycle. It's contacts are not as robust as a heat control cycling thermostat so eventually they over heat and fail (usually welded closed)
Then the thermal fuse (cut-off) on the heater blows as it is the secondary safety device.
This cuts power off to the heater.

Yes the other device on the blower wheel is also a thermal fuse.
If it blows it cuts power to the motor which shuts the unit down.

The primary heater control device is the thermistor.
It's resistance is fed to the board and then the board controls a relay (on the board) to cycle the heater element.

---

Found the basic schematic, but it does not show which line controls relay 6 for the heater. The blue wire to the heater from relay 6 goes to 110v as soon as the dryer is started, but I have yet to see it cycle off after 5 minutes of running, not sure if having the top off the dryer would be the reason. I heard a click on the control board every once in awhile like a relay was turning on and off but I had no change in the blue power line to the heater element circuit. Black wire from relay 6 is hot at all times as soon as power is on. Put the dryer into temperature test mode and see that the control board turns off the heater when the reading is 65c and I watch the temp drop all the way under 50c, but the test mode ends before it turns it back on. So it looks like the controls are working but the blue leg to the heater never loses 110v, even when the heater is off and cooling down. Not sure what I am missing there, I expected that leg to go dead when the heater is off. Still seems like everything works like it should, will have to check dryer vent temps and compare to the diagnostic temp readings.

Can anyone explain why the blue wire that feeds the heater element is not dropping power, yet the heater element is cycling off according to temps being read in the diagnostic mode? The temp drops do line up with a click heard on the control board as if a relay is turning off.

I do not know how much electrical you know so will try to keep this very basic and hopefully do a decent job explaining this.

The below assumes that all parts are OK and the door is closed.

Your house has a Neutral and two power lines (L1 and L2).
Neutral to L1 is 120 volts.
Neutral to L2 is also 120 volts.
But L1 and L2 are 180 degrees out of phase.
So when L1 is at positive 120 volts, L2 is at negative 120 volts.
Therefore L1 to L2 is 240 volts.
This is the voltage that the heater uses.

With the unit off
L1 is hardwired to the board (Black) (Pin 3 RY6).
So whenever the unit is plugged in you will see 120 volts here.
You should see 0 volts at Blue (Pin 4 RY6), relay open.
L2 will not show up here because the motor is off and the centrifugal switch is open.

With the unit on.
Again 120 volts at Black due to L1.
Lets say that the heater relay is closed then you will see 120 volts at Blue (Pin 4 RY6) This is L1 voltage.
If you measure from Blue to the far side of the heater (Red) you will see 240 volts (basicallyyou are measuring L1 to L2)
Now lets say that the heater relay is open you still see 120 volts but now it is the L2 voltage.
With the motor running, the centrifugal switch is closed so L2 feeds through it then the heater and the hi-limit and the thermal cut off.
If you measure from the Blue to the far side of the heater (Red) you will see 0 volts (basically you are measuring L2 to L2)
With a meter you have no way of knowing if you are measuring L1 or L2 so looking at 120 volts can be confusing.

With the unit running you should see:
0 volts Black to Blue (RY 6 contacts) when the relay is closed.
240 volts Black to Blue (RY 6 contacts) when the relay is open.

Hopefully the above will be useful to you.

Thank you, explained perfectly. I will confirm later today, but sounds like my control circuit is working, so in order for the high limit thermal to blow there would have to be a big discrepancy between the temperature being seen by the dryer and the actual temperature in the heater enclosure, just need to get a thermometer to compare temps. This has been a great training exercise in dryer design LOL.