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Good news on this project!
I’ve built my little device and it’s been working successfully for a couple weeks now.
I added an additional relay that also switches on when the motherboard turns on the fan. This relay (when on) completes a circuit on the MCU (GPIO to ground) just to inform it when the motherboard is powering the fan.
Here’s a sample image from my smartphone app which displays historical and real-time values:
I’ve set the device to turn the fan on for 5 minutes whenever the difference between the top and bottom shelf becomes more than 10 degrees F. I can change this temp difference value if/when I want, but I’ve left it at 10 for now. The top chart shows the top shelf and bottom shelf temps over the past 12 hours. The red bars are when my device forces the fan on and the orange bars are when the refrigerator motherboard turns the fan on.
The bottom chart shows four of the temp sensors (the chart can only show four items): Top shelf, top middle shelf, bottom shelf and the very bottom crisper drawer.
One observation I’ve made (not shown in the image above) is that if I force the fan on for a longer time than 5 minutes, the bottom shelf temp never rises as fast as it does when the motherboard has the fan on. This leads me to think that this fridge has a fan assist evaporator that’s causing the extra temp rises.
Here are two more graphs showing temps before I started forcing the fan on and after.
Quite a difference! My guess is that the real problem with the fridge is that there’s a lower thermistor somewhere that’s malfunctioned and not giving a good reading. If it were working, the motherboard would likely be forcing the fan on more often than just during the fan assist evaporation process.
Thanks again for everyone’s ideas. It’s helped a lot. In response to some of your other ideas, yes, I do have the old motherboard that they took out, but it’s way over my head to try and figure out what components do what or to determine how to modify the defrost process. (One of these days I’ll scavenge it for parts!)
I have one last question, though. When I took off the back panel of the fridge to access the circulation fan, I noticed this object in the back wall in the upper right corner. It’s about 5 inches tall. Any idea what this thing does?
Cheers,
Jim.
I’ve built my little device and it’s been working successfully for a couple weeks now.
I added an additional relay that also switches on when the motherboard turns on the fan. This relay (when on) completes a circuit on the MCU (GPIO to ground) just to inform it when the motherboard is powering the fan.
Here’s a sample image from my smartphone app which displays historical and real-time values:
I’ve set the device to turn the fan on for 5 minutes whenever the difference between the top and bottom shelf becomes more than 10 degrees F. I can change this temp difference value if/when I want, but I’ve left it at 10 for now. The top chart shows the top shelf and bottom shelf temps over the past 12 hours. The red bars are when my device forces the fan on and the orange bars are when the refrigerator motherboard turns the fan on.
The bottom chart shows four of the temp sensors (the chart can only show four items): Top shelf, top middle shelf, bottom shelf and the very bottom crisper drawer.
One observation I’ve made (not shown in the image above) is that if I force the fan on for a longer time than 5 minutes, the bottom shelf temp never rises as fast as it does when the motherboard has the fan on. This leads me to think that this fridge has a fan assist evaporator that’s causing the extra temp rises.
Here are two more graphs showing temps before I started forcing the fan on and after.
Quite a difference! My guess is that the real problem with the fridge is that there’s a lower thermistor somewhere that’s malfunctioned and not giving a good reading. If it were working, the motherboard would likely be forcing the fan on more often than just during the fan assist evaporation process.
Thanks again for everyone’s ideas. It’s helped a lot. In response to some of your other ideas, yes, I do have the old motherboard that they took out, but it’s way over my head to try and figure out what components do what or to determine how to modify the defrost process. (One of these days I’ll scavenge it for parts!)
I have one last question, though. When I took off the back panel of the fridge to access the circulation fan, I noticed this object in the back wall in the upper right corner. It’s about 5 inches tall. Any idea what this thing does?
Cheers,
Jim.
