Re: Refrigerator monitor ideas?

[AZ Woody <reply@here>]

While I've been skipping much of this thread (too much bickering), one
thing occurred to me...

The problem seems to occur when the coils "freeze up" and defrosting
doesn't occur or the drain tube is clogged.  When defrosting occurs
normally, it's clear that the moisture will travel down a tube, into
either a pan or a drain every day or so.

What if you used a moisture sensor where the tube drains?  I'm thinking
in particular, the type used as a rain sensor for an irrigation system.

It's got a spdt or spst microswitch, and disks that expand when wet.
The "trigger level" is adjustable (a set screw).

(the one I use I got from homecontrols.com, IIRC.  Here's one like the
one I use with my irrigation system:
http://www.homecontrols.com/cgi-bin/hci.pl?pgm=co_disp&func=displ&strfnbr=2&prrfnbr=788&sesent=0,0&search_id=139331)

Adjust the trigger so that it only changes state if dry for more than a
day (or what ever seems correct for your situation).

Simple, with no controller involved, with delays based on how fast the
sensor dries out, and adjustable...  And no worry about how often the
door is opened...


Robert Green wrote:
> We've got a 30 year old White-Westinghouse refrigerator/freezer in the
> basement that's cosmetically shot, but still humming away, delivering
> subzero temperatures in the icebox without major incident for years.
>
> Several times in the past 10 years or so, the drain tube from the pan under
> the freezer coils (it's an upright with a top freezer) has clogged, leading
> the coils to become caked in ice.  When this happens, the first clue is that
> the freezer temperatures begin to rise.  Other than placing a sight glass in
> the freezer floor pan, what are some simple options to detect a coil
> freeze-up condition.  I had previously had this on a yearly inspection
> schedule but the addition of a number of shedding dogs to the house in
> recent months has made that too infrequent a cycle.
>
> What I would really like to do is design something simple that can catch the
> formation of serious ice long before the coil became caked.  Simple
> temperature sensing is inadequate because the self-defrosting feature causes
> a sharp upward swing every night.
>
> The conditions that occur during a "freeze-up" (in addition to an overall
> increase of average freezer temperature each day it's building up) are that
> very little water reaches the evaporation pan at the bottom of the fridge.
> But checking that pan is about as inconvenient as unscrewing the drain tube
> connector that runs from the center top of the refrigerator to the backwall
> where it meets a drain tube that empties into the floor pan for evaporation.
>
> One thought that had occurred was to modify the drain tube to include an
> aspirin sensor between two spring loaded contacts at the top portion of the
> tube.  But I am not sure that would work because the typical mode of failure
> is an ice dam that occurs at the drain hole.  I would suspect that before
> that happens, the entire drain tube in filled with water, but I can't say
> for sure.
>
> Probably the most convenient solution would be to stick a $12 CMOS board cam
> in a baggie with some white LEDs to use as a video inspection port for the
> evaporator tray on the floor.  I'd only have to power it up during
> inspection times, so it wouldn't require a device that consumed power 24/7.
> Any monitoring of the temperature changes will likely involve a lot more
> power consumption than a video inspection "port" would.  On the other hand,
> the video evaporator inspection method probably won't tell me the coils have
> frozen until it's too late.
>
> What I really want to know is when 5 on the freezer control no longer means
> an average of X temperature in the freezer compartment.
>
> --
> Bobby G.
>
>
>