2 weeks ago ,dryer ran but didnt get hot,found thermal cut off blown, the one that is on the top part of the heating element duct. got thermal cut off kit and replaced the bad part. as i was reading on another post i now understand that i should have replaced both, i didnt replace the one w red on it, #3390291. i also read about checking for the heater to be grounded ,i removed both wires and got basically 0 on the meter, is this possible the thread said it should be about 10 ohms, also,between the connector and the case i got open ,which is what i am supposed to have.
Both thermal cut-off and high limit thermostat must be replaced together.
The normal resistance reading for the heating element should be between 7.8 Ohms and 11.8 Ohms. 0 Ohms means the heating element is shorted.
Here are the breakdown diagrams and Replacement parts for WHIRLPOOL LET7848DQ0 | AppliancePartsPros.com
Gene.
thanks for your help, I am still not sure on the testing of the heating element, my analog meter only has 2 settings, RX100, RX1K,do i need a meter with a RX1 setting in order to get a reading of 7 to 11 ohms
The thermostat on the bottom of the heater resets itself, but the fuse on the top just burns out/melts. Normally the thermostat turns off if there is a thermal oveload, but if you have poor airflow through the dryer, the fuse will blow.
Some common causes are:
Clogged lint filter, too much cloths in the drum, clogged ducting, bad drum felt seal, broken/ shorted heating element, bad cycling thermostat.
[COLOR=Blue]do i need a meter with a RX1 setting in order to get a reading of 7 to 11 ohms[/COLOR]
No the meter you have should do, even if you do not have the resolution to get a 10 ohm reading.
You are basically looking for continuity or an open on the heating coil and thermostats.
When you check for a grounded element also visually check the coil, sometimes when it gets hot it can sag and touch the case then when it cools it will open again.
Here is the wiring diagram
http://www.servicematters.com/docs/wiring/Wiring%20Sheet%20-%203401725.pdf
Also check that all the internal seals are OK re: drum etc.
The unit sucks air over the heater and through the drum, it then blows it out the exhaust. The operating thermostat is on the blower so if the unit is sucking in room air somewhere the dryer will run hot and not regulated the temperature correctly. If you cannot find a cause for the heater’s thermal fuse blowing then I would also replace the operating thermostat as odds are high that it is not regulating the temperature correctly.
Could be the operating thermostat’s contacts are welded together.
I had the dryer seeming to overheat, then it stopped running. Check with an ohm meter and the thermal fuse and thermal cutoff were blown. Then took the heating element out and saw one of the coils was touching the housing. Am going to replace those parts above now. Seems like the heating element short might have cause the whole problem
Why do you have to replace both together if one is still good?
Why do you have to replace both together if one is still good?
I am not sure what you mean by both.
If you are referring to the thermal cutoff on the heater assembly and the hi-limit, it is because the hi-limit should have regulated the temperature so that the thermal cutoff did not blow. Therefore it is replaced as it’s contacts are probably welded together.
There is no guarantee but this should not apply in your case because the grounded element probably ran unregulated by the thermostats so the hi-limit is probably OK.
The lower thermostat opens around 250 degrees, then closes after a rather long cool down period, the upper thermal fuse blows at 350 degrees, so for “normal” conditions, it never sees 350 degrees. In the event of low airflow, or a fire, or defective lower limit thermostat, the upper thermal fuse will blow.
Most of the time, the lower limit thermostat just failed to open due to a trip temperature above 350 degrees, thus it must be replaced. They both come in a kit for these reasons.
In the event of nuisance repeat fuse blowing, I have put a bunch of limit thermostats in an oven, selected the one with a lower trip temperature and the problem was solved. In these cases, however, I never found the problem as the measured air flow and cycling thermostat temperature all where “normal”. Suspect customer overloading, or the use of fabric softener sheets that clung to the back vent. I also suspected a batch of out of tolerance thermal fuses, but was unwilling to destructive test a bunch of them. Also, I have discovered erratic cycling thermostats, mostly the heated ones, and erratic, high turbulence venting.
In view of the above, anyone doing dryer repair must have a decent airflow meter or manometer and a accurate digital thermometer.
Now, My original high limit AP3131941, looks like a different part than the replacement in the kit. The original has a smaller prong (orange wire) larger prong (red wire) and another prong that attaches to the heater element. The one in the replacement kit has only two prongs the same size. How does one replace this for the original?
You did not post the model number of your dryer and it can lead to a wrong part numbers.
Gene.
I had this same problem on an old Whirlpool dryer. I followed the suggestion posted earlier in this thread and pulled the lint chute out and found a big lump of lint jammed into the bottom of the chute. Within the lump were several things that had fallen into the chute including an intact folded 8.5 X 11 piece of paper and nail clippers, among other things. I know that we were getting airflow. I don’t know how severely it was affected by the lump, but it is easy to imaging that it could have reduced the airflow enough to cause overheating (I don’t have an airflow meter). I cleaned out the lint and replaced the thermal cutoff, hi-limit thermostat, and cycling thermostat yesterday, and the dryer is working again, for now at least. We’ll see if this repair lasts long term.
Thank you for sharing your diagnosis and repair with us. Your post was very informative and instructive.
Good luck with your dryer.
Gene.
[quote=richappy;209529]The lower thermostat opens around 250 degrees, then closes after a rather long cool down period, the upper thermal fuse blows at 350 degrees, so for “normal” conditions, it never sees 350 degrees. In the event of low airflow, or a fire, or defective lower limit thermostat, the upper thermal fuse will blow.
Most of the time, the lower limit thermostat just failed to open due to a trip temperature above 350 degrees, thus it must be replaced. They both come in a kit for these reasons.
In the event of nuisance repeat fuse blowing, I have put a bunch of limit thermostats in an oven, selected the one with a lower trip temperature and the problem was solved. In these cases, however, I never found the problem as the measured air flow and cycling thermostat temperature all where “normal”. Suspect customer overloading, or the use of fabric softener sheets that clung to the back vent. I also suspected a batch of out of tolerance thermal fuses, but was unwilling to destructive test a bunch of them. Also, I have discovered erratic cycling thermostats, mostly the heated ones, and erratic, high turbulence venting.
In view of the above, anyone doing dryer repair must have a decent airflow meter or manometer and a accurate digital thermometer.[/quote]
I tried to change mine and forgot which wire goe where..is there a diffrence on which wire black or red that goes on top or bottom..
[quote=Gene;211348]Thank you for sharing your diagnosis and repair with us. Your post was very informative and instructive.
Good luck with your dryer.
Gene.[/quote]
Help I forgot which wire goes on top the red or black, does it matter??? How do you know
There is no difference between the thermostat terminals, so it does not matter.
Gene.