Sorry to belabour this issue. I have located a source of a timer with the same model number as mine, 1415435. The odd thing is that the shop has two timers with this model number, identical except for the plastic knob. They are shown on this page:
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is the third from the left on the top row, the other is the first on the second row. The top one is $93, the other is $45. You can easily see that everything about them is the same except for the knob. I queried the supplier about the price difference. His response: "Which one look like yours you need to buy that , that grey knob is there for a purpose ." In fact mine is by a different manufacturer (Paragon not Invensys), is black not white, is otherwise identical as far as I can see. The knob is shaped like the one on the $93 timer, with the two cams.
Does the knob really have a purpose? It is clear that on my fridge it doesn't touch anything as it turns.
The knob just indicates the position in the defrost cycle
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As for the pin numbering, the devices vary in the order they number the pins. The pins have defined functions. If subbing, you have to make sure you're connecting the wires to the pin function it belongs with. These substitutes are not exact visual substitutes, but "functional" substitutes. You, the installer, have to be aware how to rewire the unit when installing it. If the original was 1234 and the sub is 4321, the wiring order would need to be reversed. This is (obviously) a bitch, when the original timer has no numbers at all on it :-/
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"Basics of How a Defrost Timer Works
The defrost timer has four pins labeled from 1 to 4. Each pin has its own function in the operation of the timer.
Pin 1: The main input power is attached to pin 1. Pin 2: When in defrost mode, the power (pin 1) connects to pin 2, which activates the defrost mode. Most defrost timers stay in defrost mode for 30 minutes. Pin 3: This is your ground / neutral wire. It will be separated from the other three pins. Pin 4: When the timer is not in defrost mode, the power (pin 1) connects to pin 4, which activates the compressor and fan. Most timers stay in this mode for 10 hours.
To test if the defrost mode is working, apply voltage to pin 1. When the power supply is turned on, you should be able to measure the voltage on pin 2.
Once the timer advances past 30 minutes, the compressor and fan should turn on. You will know that the defrost timer is working if you measure voltage on pin 4 when the timer is not in defrost mode.
The compressor and fan pin should be active for 10 hours (or however long your defrost timer is designed to run). Once the 10 hours is over, the defrost timer will switch back to pin 2, activating the defrost. "
On mine, when the clockwork drive is in position and plastic gear mated, I cannot move the indicator with my fingers. However, if the clockwork drive is rotated out of position (I drilled out the two ally rivets), then I can advance the indicator in the clockwise direction, and hear "click-clunk". At the highest position on the indicator, the defrost turns on. And 30 minutes later on the dial, it turns off. The cycle repeats twice per whole indicator rotation. The whole knob rotation is not a day - it is equal to two defrost intervals or 20 hours on mine.
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The clockwork motor is 3 watts, and the gear reduction train is what raises the torque to a high enough level to actuate the snap-action cam. The switch must fall rapidly. The cam plastic must have a sharp edge, or the switch contacts could be burned. It is because of some of these design necessities that the torque level involved is excessive, and you can hear some "hum" from the motor as it struggles with its diminutive load.
Thanks Paul and John. Very helpful info, Paul. What puzzles me still is the function of the two cams. I have decided that since the cams do not contact anything on my fridge they can be ignored, as John says. The knob doesn't want to come off on mine - I didn't want to apply too much force. The markings on the two versions of the timer at that supplier are identical - both Invensys - so I don't think one is generic. It looks more like a pricing screwup at the supplier. Anyway, I found another supplier with the same (or almost the same) timer as the $93 one for $45, and I've ordered the timer and thermostat from there. They say delivery will take 5-10 days because of the pandemic. In the meantime our power bill will take a hit, because now the fridge seems to be running continuously.
On the one we had, there wasn?t a proper knob just what looked like the plastic shaft of a volume control, although the end was notched. You could turn it, not that we did, I remember the repair main rotating it when trying to figure out the problem.
That's true, but what you have to worry about more, is whether that's good for the compressor or not.
Mine seemed to be traceable to the thermostat, which had drifted out, weeks before, and took some fiddling with the knob to get it to work. And after a while, it would no longer stop.
What happened next, is it seemed the "cooling effort" was reduced, suggesting maybe a gas leak. Perhaps at the point I put it out of its misery, it was only half filled. So on the one hand, the thermostat was kaput, but on the other hand, the constant operation of the compressor, somehow led to the lost of refrigerant. I was expecting to find refrigerant oil somewhere, but did not find anything like that on the floor.
Once the fridge was put out of its misery, I put the milk in a car cooler that has a Peltier solid state cooling element in it. This runs off 12V @ 4A, and I used a PC ATX supply for the +12V. That managed to keep the inside of the picnic cooler at 2C for over a week, running off ~50W of power. But I could not put too much refrigerator content in there, just the barest necessities.
Normally, those coolers aren't all that great, but by putting it in the cool basement, the delta_T it managed to develop was perfect for milk.
Peltier coolers are horribly inefficient, so before you ask why refrigerators don't use them, it would take kilowatts to do a good job. You can get frost buildup on a Peltier, at around 20 amps of current flow, but to build a refrigerator, you'd need multiple of those. It has the advantage of moving heat, with no moving parts. But there would be heatsinks (a heatsink on the hot side, a heatsink on the cold side), and to be useful, you put fans next to the heatsinks to move the respective thermals away from the device. The fans make a hell of a noise, while the part moving the heat, does not.
I think we'd need to see if anyone has built such a fridge first, and have a look at their distribution scheme. And see how they balanced the tradeoffs.
If you use fins, then heatpipes are sure to follow. A heatpipe ensures you get the value from the fins. You can't make a fin infinitely long, because the heat doesn't want to travel to the fin end. So what they do instead, is lace the fins together, at specific lengths, with heatpipes, and the heatpipe provides excellent transport for the heat. The fin then dissipates it.
This Zalman TNN500F computer case, is totally convection cooled. The sides of the case, are giant heatsinks with fins. The heatpipes dump their heat, into the aluminium of the sides.
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That's one of the more ambitions attempts to handle heat. The upper limit there is 400W, and reasonable limits might be only about 200W of goods inside. A 95W CPU and a 100W video card maybe. But to be honest, there's room in designs like that, for *at least* one fan strategically placed. Because many electronics items make assumptions that some amount of forced cooling is present, and if you ignore such assumptions, tiny components may overheat.
Although the supplier said "5 - 10 days for delivery", the parts arrived the next day. I installed them and all seems to be working well - the fridge is cycling normally now. The timer I got is not the one I ordered. This one is Paragon (same brand as the one I've removed) not Invensys, and although the one I ordered had the knob with 2 cams (which I don't understand) this one has a simple shaft with a notch. The shaft is shorter than the replaced one, and no longer stands proud of the hole, as it previously did. This means it would be hard to change manually, but I have no idea why anyone would want to rotate it, except for testing purposes I suppose. The timer has written on is "6 hours, 25 minutes". The fridge should be good for another 20 years. A successful repair. Thanks again for all your help, Paul. I now understand how my fridge works, and in a pinch I could get a job as a fridge repairman. :)
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