Power clean heating delay issue

[potatochips]

I found two of the exact same dishwashers on Kijiji, in fact the serial numbers put them about two months apart in the production order. Anyways, both machines have the same issue. The heating delay comes on, and stays on. I tried it a few times and the machine would stick and run for an hour before I intervened and drained them. 

 

Whats interesting is that I used a temp probe to check the water temp, which went to well above 145F at 157F after 30 minutes of heating delay. I checked the thermostatic switch, as well as others I had in inventory, and all work fine when heated with a hair dryer or heating gun after one minute. I also jumpered the thermostatic switch and everything works fine, timer advances nicely. 

 

I ran the machine for about 45 minutes on a heating delay, the water temp rose from 120F to 157F. I quickly shut the machine off and disconnected the thermostatic switch and left it in place attached to the tub. No continuity. And during the shut down and disconnection process I didn't hear it trip/click if it cooled off. So its still hot. 

 

I feel like the spot where the thermostatic switch AND thermal fuse are mated against the tub isnt good and that there isnt enough heat transfer. Am I missing a step here? The machine heats fine and the switches work, just not when its attached to the machine. Ive tried other thermostatic switches with no success. What else could be the issue?

 

 

 

[stevet]

Not a valid test..

Using a heat gun or dryer really doesn't give you a true idea what the actual temperature that the bimetal inside the thermostat is closing at. You would do better if you had a small thermistor probe hooked up to a multi-meter that is placed between the tank and the thermostat, That way you can see if the spot where the thermostat is mounted actually hits the program temp or not. The thermostat will have the temp value printed on it so you can see if it is actually functioning at the proper temp. They DO go bad from time to time and while it will click when heated by your heat gun or by placing it on a light bulb, you need to know what temp is making it click.

Thermistor probes are really small and the bracket that holds the thermostat in place against the tank will hold the probe in place as well. Try that and you will see what is going on. Ironic that machine built a few weeks apart might have had the same bad run of thermostats in them.

 

[combo52]

We have run into this problem with these porclean tub WP built DWs when in water heating delay, My solution has been to put heavy fiberglass insulation under the thromostat so the thromostat can better sense the temperature in the tank and is not so much affected by the ambient air temperature under the DW.

 

John L.

 

[stevet]

Good Idea, John

I was just looking at the thermostat on my Point Voyager Kenmore and thought the same thing before reading your comment when I came back in the house. And that has to sense the temp thru a plastic tub as well. No wonder the time delay can seem like forever! If I reinstall it, I will do that. Meanwhile the spare machine is a new style Whirlpool with the removable fine strainer in the sump, which has surprised me with its cleaning ability with such a tiny wash pump in it.

 

[potatochips]

Unfortunately Steve I only have a Fluke 381, and it doesnt do temperature. However, knowing this, I timed to see how long it would take to get all three (one being brand new) thermostatic switches to temp and it took roughly the same amount of time. 

 

I did just heat all three switches up until they closed, and then measured their surface temp away from the heat gun with a temp probe. Both switches from both machines opened at 106F and the brand new one opened at 110F. I did wonder if it was something along the lines as what John had suggested, so Ill find some electrically safe insulation and see what that does for me. Thanks for the help John & Steve. 

 

[Chetlaham]

Whirlpool should have made some models without that Stats. Simpler and less that can go wrong. Lower price to compete with other machines.

 

[vacerator]

Water heater temp.

has a large effect. The dishwasher's heater can only raise the temp. one degree in ten minutes. At least back then.

 

[combo52]

WP did make DWs without this feature, they did not clean well unless your water was pretty hot but because of the shorter wash periods without heating delay they still did not clean really dirty stuff as well.

 

WP porclean tub DWs used an 800 watt heater, if the DW was well insulated on the outside of the tank it would easily raise the water temp 1-2 F per minute. With my 1987 WP PC DWs fully loaded it usually delays in the main wash 10 or 15 minutes to get from 130 F incoming temp to over 150F actual circulating temp [ If I put a # 1 plastic salad dressing bottle in the DW for washing so it can be recycled it always distorts and partly melts in the wash and rinse periods ] Note I always use air dry and because of the hot main wash and final rinse dishes are always dry even if the door is left closed over night etc.

 

Adding insulation under the thromostat was in a WP tech bulletin to solve the possible problem of a DW running to long during a heating cycle, it was usally more of a problem when the area under the machine was cold and drafty.

 

John L.

 

[Chetlaham]

Thats a bummer- not sure why they didn't use a different timer to lengthen the main wash. Maytag since the early 80s would always use a much longer main wash on their models that did not have a stat as did most other brands.

 

[potatochips]

KA machines also had thermostatic holds. 

 

[combo52]

Its Not A Bummer, Thermostats are VERY reliable, I have never seen one of these fail.

A true thermostatic hold is the best way assure perfect washing and drying results, this is just one reason why WP built DWs were superior to MT and KA DWs in performance during the 70s-the 90s.

John L.

 

[Chetlaham]

Bummer in that they did not extend the wash time on Whirlpool power cleans that did not do a thermal hold. Other brand models which did not do a thermal hold extended the main wash time on average by 10-15 minutes after the early 80s.

Maytag, Kitchen-aid and Frigidaire also made models that did thermal holds and like Whirlpool the main wash was usually shorter in terms of raw increments. But there no thermal hold models compensated accordingly.

I know stats are over all reliable, however having a BOL power clean model gives more to consumers and a lesser price IMO.

 

[johnb300m]

Something to note:
The temperature that thermostats read through plastic tubs will often have a known offset between water temp and what the "tub temp" is.
Example being, if the t-stat has to read temp through a plastic barrier, it'll have an offset value, example being, 15 degrees less or so.
Steel tubs likely read exact temp since steel transfers heat well.

 

[potatochips]

Hence why the trip temp for the thermostats are at 110F and not 140F, Johnb300m

 

Chetlaham, the Maytag WU902 extended the main wash cycle time by 13 minutes if the power boost option was selected. If you didnt select it, it would rapid advance over that section of the timer. There really is no need to extend the wash time if you ask for a thermostatic hold, the wash will already be extended while waiting for the wash water to get to the right temp. 

 

[Chetlaham]

Aren't there PowerCleans where the thermostat actually contacts the water? I know I saw that on late Kenmore model Power Cleans.

@potatochips: Right- If you have a thermal hold at any point in the main wash 10-12 minute increments are enough. But if you do not have a hold, 25-30 minutes.

 

[Chetlaham]

Here is the one I saw on those latter models:

https://www.repairclinic.com/PartDetail/Cycling-Thermostat/675740/679641

Rubber O ring to stop water from leaking out.

Here is the pump housing the stat mounts to:

https://www.repairclinic.com/PartDetail/Pump-Housing/8193525/830832

 

[Chetlaham]

This shows the other side:

https://www.repairclinic.com/PartDetail/Drain-Impeller/WP3379336/4433370