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I would like to modify my 3 year-old KitchenAid KRFC300ESS french-door (freezer on bottom) refrigerator to disable the auto-defrost cycle on a short-term basis, preferably by putting in a switch mounted near the front (ideally, connected the low-voltage control circuitry, not the defrost heater itself).

The motivation is that I'd like to be able to drive a few critical loads from a 1kW inverter, during short-term (few days) power outages. The inverter is usually able to handle these with aplomb, but during a recent power outage it could not (overloads and shuts off) even when I isolated so the fridge was the only load. I believe the auto-defrost must be the culprit.

I am a EE, and I'm comfortable going inside of appliances (in fact, I fixed a noise problem on this fridge that a tech could or would not). But I don't have the first clue how auto-defrost works, in theory or in practice.

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  • This video talks about testing the continuity of a thermostat (it's short but extremely basic): youtube.com/watch?v=zmdsBkO46dk&feature=youtu.be. Wondering if it's as simple as interrupting the path to the thermostat, probably low current and voltage ? – RustyShackleford Mar 22 '20 at 19:59
  • This (from applianceblog-dot-com) makes it sound a bit more complex though: Adaptive defrost- The control uses information from the thermistors and keeps track of number of door openings, compressor run time and length of time the defrost heater was energized during the last defrost cycle to know when to start the next defrost cycle. That can be anywhere between 9 and 99 hours – RustyShackleford Mar 22 '20 at 20:01
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    Here is what your defrost heater looks like. You can search the other parts diagrams for the fridge to see if you can find what the heater hooks up to. – JPhi1618 Mar 23 '20 at 15:21
  • Why do you believe the heater is the problem? I would guess the start current of the compressor would be a bigger problem. Starting current for motors can easily be 3-4 times nominal current. This may be enough to trip a 1kW inverter... – vidarlo Mar 23 '20 at 18:04
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    Defeat, Not bypass, temporarily disable, circumvent, sidestep, or render incapable but Defeat ! Yea, even vanquish thee O Auto-Defrost. – Alaska Man Mar 24 '20 at 2:53
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Auto-defrost just raises the temperature enough that the accumulated undesired ice build up (very thin at this point) melts away while still cold enough and short term enough to not melt the items frozen in the freezer. It does this with a heater inside the fridge to periodically warm the appliance during the defrost cycle. Here's a video that explains it.

If you want to disable, you can find and remove or cut the wire to the heater. There should be a wiring diagram on the back and probably down low. Due to your background, I think that you can take it from here

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  • Thanks. Seems like it'd be better to disable the control of it though (e.g. by interrupting the thermostat), as I imagine the heater wires would have higher voltage and/or current. – RustyShackleford Mar 22 '20 at 20:06
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    ? I don't think that the thermostat has anything to do with the defrost cycle. It's going to either be purely timer based or based on how often you open and close the freezer. – Ack Mar 22 '20 at 20:09
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    Another comment to post an idea I just had. I suggest inserting a switch on a low voltage part of the circuit that you are going to modify so that you can turn it on and off again without opening things back up again. – Ack Mar 22 '20 at 20:35
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    Oh yes, that. exactly what I intend to do. Sounds like I need to edit OP for clarity :-) – RustyShackleford Mar 22 '20 at 20:48
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    Probably in the same compartment with the light, if you have one in your freezer, or behind an obvious panel – Ack Mar 22 '20 at 23:38
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At the rear of the freezer compartment there is a plastic cover held on with 4 screws. Behind that I should find the evaporator coils, and the defrost heater will be attached to that. If I add a small SPST switch in series with the heater, thing will function normally when the switch is closed. If I open the switch, the heater cannot operate.

During power outages when I'm trying to power essential house loads with the 1kW inverter, I'll open that switch. Seems like the worst that can happen is that the evaporator coils ice up; I can help that not to happen by avoiding door openings. But if it does happen, I'm no worse off than in the olden days before auto-defrost. I'd have to unplug the thing for awhile (perhaps a day) and let the coils defrost. Also, it appears the heater runs off 120vac, so I need to be careful with the way the switch is wired and mounted.

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  • To have the switch operate at low voltage, I'd have to get into the control circuitry in the rear of the unit. Cpmplicated, and there no reason I shouldn't be able to make the simpler line-voltage solution safe. – RustyShackleford Mar 24 '20 at 2:05
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As far as the thermostat, my GE frig monitors air temp leaving the evaporator coil and the temperature rise that occurs when the ice is gone indicates the defrost cycle can end. I learned there is also a defrost cycle on power-up before the compressor will kick in. It's annoying when you're in a hurry to see the compressor run but goes fast if there's no ice present.

My idea is to interrupt the 12v going to the defrost relay. It's a bit trickier than putting a switch in line with the heating element, but a wider variety of switches and lighter gauge wire would get it done. I may even use an opto-isolater.

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