So I noticed some washability and drying issues creeping up shortly after re-installing the KUDD23.
After some monitoring and temp measurements, I noticed that the main wash was just not heating up in the main wash like it used to.
Previous observations showed that the thermal hold would trip around 135F and by time the rest of the 6-7min wash period was advanced, the water was about 140F.
This time, I noticed that the thermal hold would not hold anymore in the main wash, or maybe hold for like a minute, then advance. Leaving me with end-of-wash temps only around 130-135F.
With some ChatGPT sleuthing, and knowing this original thermostat was over 30yrs old, it was looking like it just reached end of life, and GPT said that these snap-disc bi-metal thermostats fatigue with old age, tripping earlier than required.
I was able to confirm this by filling the machine, letting the water cool to below 100F, and letting it run a wash cycle. It did thermal-hold and heat till about 115F, and then it advanced, giving me water temp of just over 120F after the main wash.
So I started a hunt for a new thermostat.
I tried looking for other OEM dishwasher thermostats, but by this time in history, they're all only "high limit" thermostats 180F to over 200F. Everything has moved to digital thermistors now.
I found some HVAC snap disc thermostats, and found one that's in the "normally open" 120V range with my amperage, and it has a 140F trip point. Which means I should be able to get at least 140F or more, water temp in the main wash again.
I also thought there might be some thermal lag, even though the steel tub very quickly takes on the temperature of the water.
So I got another one, at lower temp, and what's neat bout this one is it's adjustable.
This one adjusts from 90 - 130F with a screwdriver dial on the back. I figured, if there's an amount of thermal lag, then 130F should be a good max.
When I installed it, I set it to 125F, so as to avoid any temp overruns again.
Lo and behold, when I ran another test wash, it was cutting out right at about 125F, and only getting to the low 130Fs again at end of wash. So this thermostat was more accurate, and maybe I didn't have the thermal lag I thought.
I bumped up the temp setting to 130F, the max this unit will now no, and re-ran the test.
It advanced from thermal hold almost as early as before, not getting to the ~140F I wanted.
At this point, I thought, ok, I don't really have a thermal lag problem, I'm either fighting a switch tolerance span, or maybe I didn't mount the 140F t-stat properly. So I re-installed the 140F, and ran it again last night, in fact.
I got similar results as with the first time. The thermal hold ran for over 25min, and by the end of the wash period, the water was 154-155F.
Just a tad too hot for what I'm consistently looking for.
This confirms to me, I think, that the tolerance on this 140F unit is almost 10F too high on the + side.
Mounting the Thermostats
Something I didn't mention yet is how I'm holding these vastly different thermostat models.
I had to devise a 3D printed holder that would mount with the current thermostat mounting bracket under the tub.
You can see that here: This is actually Rev. 2, to hold both versions.
These are photos of Rev 1:
Here is the photo of model Rev 2, that mounts the same way:
I even was able to get the legit KA logo typeface on this one.
Data
Here's the data recorded from the various tests.
If you do a little math, you can see that the 800w heater is working well, and heating the tank of water about 1deg, per minute.
Steps Forward
I think I'm going to look for yet another thermostat that can get me more at the target ~140F temp I'm looking for.
I'm not really in favor of running this 30+yr old machine to 155-160F temps on a regular basis. Seems harsh and I don't want to subject some of my dishes to that, nor pay for that energy constantly.
If I can dial this in, this will get me good 140-145F washing temp, and 20-25min total main wash times, which is what seems to be in-line with OEM design.
White Rodgers has another series of adjustable thermostats that go from 140 - 180F, I could maybe try that and hope it's tolerance range is tighter and closer to the 140 limit.
Or get another 140F single temp thermostat, hope the tolerances are better on that one.
Or keep searching for different types......
After some monitoring and temp measurements, I noticed that the main wash was just not heating up in the main wash like it used to.
Previous observations showed that the thermal hold would trip around 135F and by time the rest of the 6-7min wash period was advanced, the water was about 140F.
This time, I noticed that the thermal hold would not hold anymore in the main wash, or maybe hold for like a minute, then advance. Leaving me with end-of-wash temps only around 130-135F.
With some ChatGPT sleuthing, and knowing this original thermostat was over 30yrs old, it was looking like it just reached end of life, and GPT said that these snap-disc bi-metal thermostats fatigue with old age, tripping earlier than required.
I was able to confirm this by filling the machine, letting the water cool to below 100F, and letting it run a wash cycle. It did thermal-hold and heat till about 115F, and then it advanced, giving me water temp of just over 120F after the main wash.
So I started a hunt for a new thermostat.
I tried looking for other OEM dishwasher thermostats, but by this time in history, they're all only "high limit" thermostats 180F to over 200F. Everything has moved to digital thermistors now.
I found some HVAC snap disc thermostats, and found one that's in the "normally open" 120V range with my amperage, and it has a 140F trip point. Which means I should be able to get at least 140F or more, water temp in the main wash again.
- So I got this model:
https://www.supplyhouse.com/White-R...trol-Cut-In-140-Degrees-F-Cut-Out-120-Degrees
I also thought there might be some thermal lag, even though the steel tub very quickly takes on the temperature of the water.
So I got another one, at lower temp, and what's neat bout this one is it's adjustable.
This one adjusts from 90 - 130F with a screwdriver dial on the back. I figured, if there's an amount of thermal lag, then 130F should be a good max.
When I installed it, I set it to 125F, so as to avoid any temp overruns again.
Lo and behold, when I ran another test wash, it was cutting out right at about 125F, and only getting to the low 130Fs again at end of wash. So this thermostat was more accurate, and maybe I didn't have the thermal lag I thought.
I bumped up the temp setting to 130F, the max this unit will now no, and re-ran the test.
It advanced from thermal hold almost as early as before, not getting to the ~140F I wanted.
At this point, I thought, ok, I don't really have a thermal lag problem, I'm either fighting a switch tolerance span, or maybe I didn't mount the 140F t-stat properly. So I re-installed the 140F, and ran it again last night, in fact.
I got similar results as with the first time. The thermal hold ran for over 25min, and by the end of the wash period, the water was 154-155F.
Just a tad too hot for what I'm consistently looking for.
This confirms to me, I think, that the tolerance on this 140F unit is almost 10F too high on the + side.
Mounting the Thermostats
Something I didn't mention yet is how I'm holding these vastly different thermostat models.
I had to devise a 3D printed holder that would mount with the current thermostat mounting bracket under the tub.
You can see that here: This is actually Rev. 2, to hold both versions.
These are photos of Rev 1:
Here is the photo of model Rev 2, that mounts the same way:
I even was able to get the legit KA logo typeface on this one.Data
Here's the data recorded from the various tests.
If you do a little math, you can see that the 800w heater is working well, and heating the tank of water about 1deg, per minute.
Steps Forward
I think I'm going to look for yet another thermostat that can get me more at the target ~140F temp I'm looking for.
I'm not really in favor of running this 30+yr old machine to 155-160F temps on a regular basis. Seems harsh and I don't want to subject some of my dishes to that, nor pay for that energy constantly.
If I can dial this in, this will get me good 140-145F washing temp, and 20-25min total main wash times, which is what seems to be in-line with OEM design.
White Rodgers has another series of adjustable thermostats that go from 140 - 180F, I could maybe try that and hope it's tolerance range is tighter and closer to the 140 limit.
Or get another 140F single temp thermostat, hope the tolerances are better on that one.
Or keep searching for different types......
