Half a croissant, on a plate, with a sign in front of it saying '50c'
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Fridge Door Check System Sound

When is a fridge door not a door?
  [vote for,

I realize that these ideas may be interpreted as having been posted in somewhat similar fashion around the HB, but I'm assembling them, and adding specifics I've not found in other posts. If this isn't a sufficiently different enough instantiation of these ideas, please MFD.

Over the weekend, my dedicated freezer had built up so much frost that the door was held barely ajar, and was thusly not at all a door anymore.

This allowed in more damp basement air (eew), which resulted in more frost, which pushed the door open further. Once found, I was required to dispose of quite a lot of food which I would have preferred to have eventually eaten. Particularly upsetting was the loss of a vegetarian "fish ham" that looked quite intriguing, as well as 5 lbs of high quality broccoli.

Food loss aside, manually defrosting that thing was quite unpleasant as well.

My fridge sensor is a two part device to prevent such catastrophic food loss:

Two small square metallic strips are mounted to the corners of the rubber gasketing on the open side of the fridge door. They are conductive, and are so small that they fit inside the inner half of the gasketing, thusly not compromising the integrity of the seal. They make contact with similar strips on the fridge frame. A microcontroller based circuit watches them, and if they are broken for more than, say, 2 minutes, sounds an alarm that grows increasingly more audible and obnoxious as time goes on.




and so forth.

Since the frame near the gasketing on fridges is traditionally warmed with either a warming wire or some of the fridge's own ex-heat, conductivity inhibiting frost will not build up on the sensors.

It should be mentioned that the normal "door switch" would not have helped in this situation because the door was only ever so slightly held open by the ice buildup.

This will prevent most failures, but there is a backup mechanism:

The monitoring circuit board also watches the compressor via an input from the compressor's own relay, and if the compressor has been chugging away for a higher duty cycle than:

1) it should be going for based on its design

2) the amount of time it should be on for based on a properly operating fridge

then it will throw a similar style error, with a different tone to indicate to the user that even though the door may be shut, there is still a problem, possibly:

1) leaked refrigerant

2) damaged thermostat

3) compressor seal failure

4) some jackass put a bucket of hot pudding in the fridge

5) something else

The "advanced" model will include an OBD-II compliant connector to which the user can connect a standard car code reader to check the error code on the processor. This model will have more sensors to help determine the mode of failure:

pressure sensor for refrigerant

a to d reading a coil wrapped around the power line of the compressor to see how much current it is drawing (too little could mean a broken coupling, too much could be a seized/tight/ungreased bearing)

thermocouple output reading

Lightbulb status: Burnt out, on or off -- so the user can determine whether or not the bulb does extinguish when the door is closed.


The super-advanced model will include an LCD which reads out the problems/status on a small character display.

It is also capable of outputting fridge use,

time open/closed,

energy consumed, current time/temperature,

and how you look like you're losing weight lately -- maybe you deserve that slice of pie?

All of the error codes will be present in the standard manuf. manual, unlike my car, which I needed to buy a $80 book to get the codes for.

ericscottf, Jun 01 2009




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