The Mystery of the Mysterious Miele Malady

David Oliva

RD Appliance Service, Corp. PO Box 234, Bethpage, NY, 11714

Recently RD Appliance Service was briefly confounded by a  Miele washer, a W1918, not exactly the latest model.  The complaint was that the washer would not spin out the clothing at the end of the cycle, it would leave them sopping wet.  Sometimes, if the customer re-ran the cycle the washer would spin.  So, armed with all of the necessary technical documentation and diagnostic equipment I ventured out to the home.

Upon arrival I opened up the service manual on my tablet, placed the machine into service mode and proceeded to run a spin test.  The tub spun up to high speed without a hiccup.  Hmmm, I thought.  So I exited service mode and just ran a regular spin cycle, and again the washer spun.

After questioning the customer about her use of the machine I concluded that the machine was sometimes being overloaded and that this was causing it to be unable to balance itself, thus preventing it from spinning.

Not so.

She called back the next day with the same problem, and again when I arrived the problem would not occur.  So I needed to do some more in depth research on this issue as this is no “Just replace it” type of washer, they retail for $2000 or more.  With some helpful tips from my fellow appliance technicians at appliantology.org I returned armed with more knowledge and we got it figured it.

My father and I both went back on this, two heads and all.  I called the customer about an hour before we were going to arrive and had her start a wash cycle.  This worked out well because we arrived just at the end of the cycle and found the washer not spinning.  Finally!  No spin at the end of a regular cycle, no error codes flashing.  Set it to a spin only cycle, no spin.  Put it in test mode and ran a spin test, no spin.  Alright, now we’re getting somewhere.

So, we opened up the front of the machine (thank you Miele for making the whole front panel open on a hinge!)  in order to find out if the motor was getting voltage, which would indicate a problem with the motor itself. However, this old Miele technical info does not include voltages for the motor, and the wires are all the same color and not labeled, same goes for the connectors.

We knew it uses a single winding DC motor, but that’s about as in depth as Miele gets regarding the motor.  So after exercising our finely honed diagnostic skills we determined which two wires were the motor voltage supply wires and we attached the voltmeter leads to them near the lower electronic (secondary control board).

We once again put the machine into spin and the damn thing started spinning again.  This, however, showed us the voltage used by the motor when it is working, and this is crucial information.  In case you are interested it uses ~16-20 VDC on tumble, changing polarity as it switches directions, then the voltage ramps up to a whopping 195 VDC on max spin.

Ok, so we know the motor works, but we still don’t know what’s wrong with the washer.  We began doing basic diagnostic checks once again, check and clear drain pump trap, check pressure switch hose, etc.  Nothing.  So we ran another test cycle.  This time allowing it to fill and tumble and then move to drain and spin.  Aha!  Now it won’t spin.  It tumbles a little at 16-20 VDC, then stops and won’t spin, no voltage to the motor.  Ok, good.  I suggest checking the pressure switch again.  So my father tapped the pressure switch and voila!, it starts spinning, and reads all the way up to 195 VDC again.  Yes!  The pressure switch was sticking….sometimes.

So, we’ve replaced the pressure switch and the air trap with the pressure switch hose and that old school, quality German washing machine is running like new once again.

RD Appliance Service, Corp.  Long Island Appliance Repair Since 1963.  We are committed to constant improvement in our skills as appliance repair technicians.  The above is an article detailing some of our self education in matters of appliance repair diagnostics, an area in which we strive to be the best in the business.  If you need an appliance repair anywhere in Nassau County call RD Appliance Service, Corp. at 516-561-0523 or visit our website at http://www.rdapplianceservice.com.

Centrifugal Pumps and Cavitation

David Oliva

RD Appliance Service, Corp. PO Box 234, Bethpage, NY, 11714

I recently had a customer whose washing machine would not drain. I attributed this problem to the excess of suds in the tub. The customer seemed skeptical of this diagnosis and so this problem seemed like a good topic to delve further into.

Oversudsing issues are very common in washing machines and dishwashers. Using the incorrect type, or an excess, of detergent can cause an oversuds situation. This often leads to drainage problems. The drain pump cannot pump out overly sudsy water. But why not? It’s because of something called cavitation.

Cavitation is the formation of vapor cavities in a liquid. Washing machines and dishwashers use centrifugal pumps. A centrifugal pump needs an uninterrupted supply of water to function properly. The spinning impeller causes the water inside the pump to spin as well, creating centrifugal force, which causes the water to flow away from the center, or inlet, of the pump and out of the discharge port. This displacement creates negative pressure which sucks more water into the pump. Introduction of suds, which are mostly air, into a spinning impeller will interrupt the flow of water and introduce air into the system, disrupting the vacuum being created, and ultimately preventing the pump from being able to discharge the water. This will not be resolved until the suds are eliminated. Fabric softener or vegetable oil can be added to the machine to help to eliminate the suds and allow the pump to finish draining the water.

The video below is a brief introduction to the way in which centrifugal pumps function.

RD Appliance Service, Corp.  Long Island Appliance Repair Since 1963.  We are committed to constant improvement in our skills as appliance repair technicians.  The above is an article detailing some of our self education in matters of appliance repair diagnostics, an area in which we strive to be the best in the business.  If you need an appliance repair anywhere in Nassau County call RD Appliance Service, Corp. at 516-561-0523 or visit our website at http://www.rdapplianceservice.com.

IR Thermometers and Emissivity

David Oliva

RD Appliance Service, Corp. PO Box 234, Bethpage, NY, 11714

http://www.rdapplianceservice.com

“Emissivity is the measure of an object’s ability to emit infrared energy. Emitted energy indicates the temperature of the object.” That definition is from an article on Rayteks website titled Emissivity of Most Common Material. I only recently learned what emissivity meant, and because of that I’ve been using an infrared (IR) thermometer for over a decade and it seems that only now am I able to use it properly.

IR thermometers measure surface temperature, not air temperature, and so it is important to know both the emissivity value (EV) of the material you are measuring and the emissivity setting (ES) on your IR thermometer. Some IR thermometers have a programmable ES, for instance the Fluke 62 Max, which is adjustable between 0.1 and 1.0. Others have preset ES, usually at 0.95. An EV of 1.0 means the material gives off no radiation, this is known as a “black body”. The lower the number the more radiation the material emits, and the materials with EV of 0.99 and below are known as “gray bodies”. Wood, for instance, has an EV, depending on species, of between .88 and .96. Polished aluminum, on the other hand, has an EV of 0.04 – 0.05.

To better understand what this means in practical terms I performed a simple experiment. I set my oven to 350ºF. I used a Fluke 62 Max to take measurements at the back wall of the oven after it was preheated. I did this three times for each ES, in increments of 0.1, from 0.9 to 0.2, and averaged the three readings. Below is a graph of the results.

Posted Image

The graph above shows that at the highest ES the readings were quite accurate, and this makes sense because the EV of steel is 0.8-0.9. But by 0.3 the temperature readings were off by almost 400ºF. And at a setting of 0.2 the thermometer was incapable of reading anything because it surpassed the maximum readable temperature of the 62 Max, which is 932ºF, almost 600º higher than the actual temperature.

It’s easy to see how using an incorrect setting could give a very inaccurate reading and how important it can be to align your thermometers ES with the actual EV of the material you are measuring. In many cases the default ES of 0.95 will be suitable as most materials appliance techs are working with, plastic and steel, have an EV of between 0.85 and 0.95 anyway, so it will get you pretty close. But other materials we encounter, such as aluminum, brass and copper have much lower EV and an ES of 0.95 will not garner accurate measurements.

Further Reading

Emissivity Coefficients of Some Common Materials

IR Education: Emissivity

The Principles of Noncontact Temperature Measurement (PDF)

RD Appliance Service, Corp.  Long Island Appliance Repair Since 1963.  We are committed to constant improvement in our skills as appliance repair technicians.  The above is an article detailing some of our self education in matters of appliance repair diagnostics, an area in which we strive to be the best in the business.  If you need an appliance repair anywhere in Nassau County call RD Appliance Service, Corp. at 516-561-0523 or visit our website at http://www.rdapplianceservice.com.