User:Jstapko/personal/MaytagDishwasher

Dishwasher Repair

Introduction
This project was an effort to find out why our dishwasher was leaking water all over the floor (and hopefully fix it). It was ultimately decided to scrap the dishwasher because the door was very rusty from age and a long standing water leak, and the motor's start winding was burnt out, requiring a new motor at a very minimum. This wiki is to consolidate information gathered for this project so that someone may benefit from the direction of this dishwasher.

Specifications

 * Manufacturer: Maytag
 * model: DWU4912AAB
 * serial number: 10211132QK

General Information Sources

 * 1) Google Images
 * 2) PartSelect - quality images of parts, so I can see what the part looks like before disassembling to access it
 * 3) searspartsdirect - has assembly diagrams, parts lists, and parts numbers
 * 4) ebay - ebay can be an excellent source of images for parts to help understand how they work, even if the part is discontinued and not available on appliance repair sites
 * 5) repairclinic
 * 6) youtube - LOTS of videos about disassembling and repairing maytag dishwashers

Subsystems

 * 1) Intake solenoid valve - allows water to enter from hose
 * 2) Spray arms - Forces water against dishes hard enough to dislodge dirt.
 * 3) Water Pump - Serves to recirculate water for rough cleaning, push water through spray arms, and drain dirty water.
 * 4) Timer - motor driven mechanical timer with switches that activate all other components at the proper times
 * 5) Float switch - Turns off intake solenoid in the event of the tub getting too full
 * 6) Heater - Heats dishes to help them dry
 * 7) Blower - circulates air over dishes during dry cycle to help them dry
 * 8) Temperatur sensors - one cuts power to the heater in case of overheating, the other
 * 9) Wax motor - special, solenoid like device that opens soap door

Wax Motor
In this dishwasher, a wax motor is used to release the soap door latch and to release the rinse aid liquid. A wax motor consists of a cylinder and a piston containing wax with a high thermal coefficient of expansion. Heating the wax (in this case, with electricity) causes it to expand, pushing the piston, which can then do useful work. For a more detailed description of a wax motor's operation and applications, see the Wikipedia page on wax motors. For the original explanation that enabled me to understand the wax motor, see SublimeMasterJW's "Wax Motor 101" page. For teardown photos of a wax motor more similar to the one pulled from this dishwasher (same color, parts, see this thread on appliancejunk.com. The round disc visible on the appliancejunk.com page is the "positive temperature coefficient"  (PTC)resistor.  Positive temp. coefficient means that as the part heats up, its resistance increases, reducing the current flow through it.  In a conventional solenoid, actuating current is reduced after pull in because the air gap between the armature and the core gets shorter, which increases the permeability of the magnetic circuit.  This, in turn, causes and increase in the inductance, which reduces the current flow.  Since the wax motor has no coil, it uses the PTC resistor to reduce the current after activation instead.  To purchase wax motors, check appliance repair websites.

Timer
All of the dishwasher's functions are controlled by a mechanical timer driven by a very slow electric motor. In an effort to understand it, I looked online for pictures of one someone else had already disassembled, to see if there were springs, small gears, etc. that I should consider when trying to disassemble mine. I found this tutorial at automaticwasher.org showing a completely different type of timer disassembled, but it gave an excellent explanation of how the motor advances the drum, which is essentially the same in the timer from this dishwasher. Also found a justanswer.com thread showing Kingston style timer with photos of the advance mechanism in place, further showing how it works. The timer for my machine worked more like this one, the major difference being that the cam lobes are on a drum, not a disk as in the Kingston/GE types in the first 2 tutorials I found.

The basic principle is that a very slow speed synchronous motor drives the advancing levers shown at the automaticwasher.org page, pushing first one, then the other away from the motor shaft. The ends of the levers have ratchet (one direction) points that engage teeth on the edge of the timing disc/drum, as shown on the justanswer.com page. One turn of the motor advances the disc/drum one or two clicks. The protrusions on the disc, which can be as long or as short as desired, activate the switches. Each ring or cam disc can activate its switch at any part of the cycle, and any number of switches can be activated at a given time, or in a given order. The switches activate the electrical parts of the washer to give the proper sequence of events (such as first fill with water, then run pump, then open soap door, etc.

Molex Ground Clip
Found an unusual connector on one of the control system ground wires. I identified it by searching online for connectors, then browsing images. I followed the most similar images i could ultimately to TEConnectivity's website, where I found that a similar connector was called a "ground clip." Then, I started a new search using that as the terms, and Google Images returned the connector very early in the results. It turned out to be a Molex ground clip.

Failure Analysis
Several problems contributed to the death of this dishwasher. Briefly, they are:
 * Corrision
 * Lack of care or preventative maintenance
 * Burnt main motor

Corrosion
Several areas of the dishwasher, particularly the door, were badly corroded, which meant that it would have been an economically unsound decision to invest in parts for a machine that may have had only a few years left anyway. Corroded areas were mostly the door, with some on the access panels and blower motor mounting plate. [have pics of these] User Norman Hochfeld claims in This thread at servicetechhelp.com that one possible cause of this corrosion is a clogged lower spray arm. His description of the failure mode is also consistent with the water leakage problem that this project was intended to resolve. Other posts on the servicetechhelp.com page suggest that a bad door seal could also cause the water leakage, and ultimately corrosion, problem.

Burnt Motor
A close visual inspection of the pump motor showed that insulation on one of the start windings was badly discolored, black in most places, with apparent charring and peeling. This very strongly suggests that that start winding is burnt, and this is consistent with the fact that in initial testing, the lower spray arm would turn very slowly during part of the cycle. It is not yet known why this winding failed, but suspected causes include:
 * age
 * 1) clogged pump filters
 * 2) running the pump without water in the dishwasher
 * 3) water from the dishwasher leaking on the motor

Preventative measures might include:
 * 1) clean debris out of spray arm nozzles (to reduce mechanical resistance to mnotor shaft turning)
 * 2) clean the pump filters
 * 3) check regularly for leaks

Other Topics to Cover
If I had more time, I would discuss:
 * 1) Molex grounding clip (funny shaped electrical connector for pushbutons)
 * 2) The wax motors (have to links to add)
 * 3) Shaded pole motors - including varying speed by tapped windings or variable voltage
 * 4) the main motor, with its burnt start winding
 * 5) The soap door mechanism
 * 6) the little clip at the end of the dish rack track
 * 7) the lock ring
 * 8) the door spring tensioners
 * 9) the radiant shields