Does current draw of one fridge affect another fridge’s microprocessor if both fridges are on same circuit?

Question

Two fridges are on one circuit. Not sure the exact amps, but 15-20 amps is probable.
When the compressor of the one analog fridge starts, and pulls current, some of that current goes to the other fridge inevitably. So when it reaches the electronic board, what message does it relay to that electronic board?
I replaced the temp twice on that fridge evaporator and after 3 weeks it still ices up and the evap fan knocks against the ice. I could replace the board but wanted to know if the ‘shared circuit issue’ is a possibility for why that defrost cycle is not working properly.
In other words, is the current going to the microprocessor of the board ‘confusing’ it?

Answer 1

TL;DR No

As long as all wiring is done the normal way, there is almost no effect on devices on a circuit from other devices on a circuit. The current does not flow through one device to get to another. In fact, when wiring is done in series rather than parallel all kinds of strange things can happen. Note that a series of receptacles is not actually normally series wiring - the wires chain from one receptacle to the next in effectively a parallel configuration, even if it doesn't seem that way from the outside.

There are a few situations where one device can affect another on the same circuit:

• Too much current draw at one time

I used to have this with computer + laser printer + refrigerator/freezer + freezer + lots of lights and stuff all on one circuit. I partially fixed it by installing a UPS on the computer so that voltage dips caused by the laser printer starting up (combined with everything else) wouldn't reset the computer. I permanently fixed it by having my electrician split the circuit so that the computer + laser printer are on one circuit and everything else is on another circuit. Note that the circuit breaker (actually fuse at the time) never tripped because the current never went much above 15A, but even at a somewhat lower level there was some dimming of lights and other problems.

If all you have on the circuit is two refrigerators and some lights then this is probably not a problem. Testing voltage variation when the refrigerator compressors start will tell you if this is a problem or not.

• Interference

This can take the form of spikes, surges or other problems caused by large motor loads. While the refrigerator electronics should be protected (after all, they have to deal with their own motor loads), it is possible particularly for an older refrigerator to cause problems for a newer (more sensitive electronics) model.