Washing machine door lock

[Jimk]

Self isolating? :-)

[Dave W]

I don't need help, but I'm writing this account in case it interests or helps others.

I bought my Candy washing machinein 2011 because its front to back depth is only 40cm whereas all other makes and models are 50cm. Ever since new the door catch didn't always register as closed, and I had to press the case slightly with my knee to make it register.

Recently I decided to do something about this, and removed the door switch for examination. I found an adjustment screw that put variable pressure on the spring contact arrangement, to make it snap either open or shut. In one position, a plastic block stood 1mm above the surface, and in the other the block was flush with the surface.

The door hook pushes a plastic slider across the block to depress it, so I thought that the screw should be adjusted to make the block pop up, otherwise the door would never operate it. Then it seemed that the block was catching in the apertures in the slider, so I filed a slope on the slider so that it could freely slide in and out, and either allow the block to rise into an aperture or get pushed down by the solid part of the slider.

This worked great - I no longer had to use my knee.

However the door lock indicator now showed that it had not been released after the wash. It was no trouble, because the door had never been locked anyway!

So I reinvestigated the switch. There are three wires into it. Two of the wires go to the contacts, but did the third one that looked like an earth do anything? I thought there ought to be some sort of solenoid to act as a lock, but the switch is far too light for a heavy solenoid.

The third wire went to the adjustment screw, which pressed on a U-shaped metal piece cradling a thin metal strip by its ends. In the middle of the strip was a white spacer about 7mm dia by 3mm thick, which pressed on the switch. Now it dawned on me. The spacer is in fact a 1K resistor, which can be heated by current, bending the thin bimetallic strip and flipping the switch into the opposite position.

So the adjustment screw has to be set for the plastic block to be flush when cold, not proud. When the machine is set going, the resistor gets heated and the plastic block is biased up to be pressed or not pressed by the slider. Throughout the wash the block stays proud, preventing the slider from returning. Now I had to negate my filed bevel by sticking on a shaped bit of tin to recreate the original sharp edge of the aperture in the slider.

I tried a trial run with the switch out in the open so I could see what happens to the plunger. Right enough it popped up at the start, but didn't pop down afterwards when the resistor cooled down. However a further adjustment of the screw made it pop down again.

I still don't know why I had to put my knee on it - perhaps the adjustment screw wasn't quite set so the plastic block popped up reliably, requiring a bit of distortion from my knee.

[Brian Gaff (Sofa 2)]

This design sounds a bit of an afterthought. My Panasonic has a solenoid you can hear it quite clearly. Brian

[ss]

Excellent, thats the type of result I like to read about. I just dont have it in me to buy a new part until I have tried to repair it, more so if we are talking mechanical rather than electronic.

[Harry Bloomfield, Esq.]

Dave W was thinking very hard :

They use a wax capsule/ plunger system on some door interlocks. Yours sounds like one of those. A resister heats up a wax capsule, the wax expands and forces out a plunger. Plunger retracts slowly, once the heat from the resistor is turned off - so there is always a few seconds delay between pressing the start button and the actual start, plus a delay after the machine has finished, before the door can be opened.

[Brian Gaff (Sofa 2)]

I think what irritates me is when a very firm metal design of say, a drawer runner is fixed in with cheapo plastic brackets that sooner or later crack and fall to pieces. Brian

[Dave W]

Most other machines (including Panasonic) use the same or similar switch. I assumed mine had a solenoid which I "could hear quite clearly", but in fact the click was the switch popping down when it cooled down, kicking the slider out on its spring.

I've now seen many articles on Google on how the switch works and how to change it - I wish I'd seen them before tinkering with mine.

I did see a picture of an AEG lock that includes a solenoid.

[Andy Burns]

My first two "british" Hotpoint washer dryers had an interlock based on the drum rotation, you could open the door the instant the drum stopped, now my "italian" Hotpoint makes me wait a couple of minutes before I can grab a shirt in a hurry ... progress huh?