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Old 09-11-2012, 05:48 AM   #1
mj_b90
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Default Mini Fridge Fermentation Chamber - Very Short Cycle

I recently cut the door shelving off of my mini-fridge to fit a bucket and wired up an STC-1000 for fermentation.
I finished all this at the end of my current fermentation so I was going to use it to cold crash first, but it seems like the fridge's cycle length is too short to do any real cooling past ~10 C. The temp controller is set to 0 C so it has left power to the fridge on for the last several hours but the fridge is cycling pretty regularly at 6 minutes on, 4 minutes off.

I used to notice that it would be switching on and off a lot but never noticed just how short it's cycle was. Does this mean there's something wrong with this refrigerator? It's a Haier 4.6 CuFt model HNSE05BB. Has anyone seen this short of a cycle from their fridge before?

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Old 09-11-2012, 05:58 AM   #2
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Does the fridge have a manual adjustment for temp? If so make sure it's to the coldest setting otherwise it could be reaching the manual set point and shutting the compressor off before you're reaching the set temperature on your temp controller.

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Old 09-11-2012, 06:07 AM   #3
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It does, and I had it set to 7 of 7 thinking that was the coldest. I will turn it back to 1 for a bit and see if it changes at all.

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Old 09-13-2012, 02:23 AM   #4
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After checking the manual 7 is the coldest setting so that can't be it. But setting it to 1, 4, or 7 didn't seem to make much difference to the timing. Is it possible that the compressor is overheating and cutting out until it cools down?
I'm measuring temp with the probe in a beer bottle filled with water and it seems to have bottomed out at 5C and holding there. Could it be that this fridge won't get down much lower than that?

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Old 09-13-2012, 04:24 AM   #5
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I suppose thats a possibility. What is the hysteresis of your temp controller. Most people set theirs to 1 degree. If yours is set higher that could be another cause of it shutting off around 5C

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Old 09-13-2012, 01:29 PM   #6
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Quote:
Originally Posted by GilSwillBasementBrews View Post
I suppose thats a possibility. What is the hysteresis of your temp controller. Most people set theirs to 1 degree. If yours is set higher that could be another cause of it shutting off around 5C
That's not how differential or hysteresis works. Once the system calls for cooling it is supposed to bring the temperature down to the set point and then shut off until the temperature rises by the differential/hysteresis setting.

Nobody has asked, so I will: where is the temperature probe for the STC-1000 located?

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Old 09-13-2012, 04:01 PM   #7
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The probe is in a beer bottle filled with water, and differential is set to 0.5C. But I know the problem is with the refrigerator and not the controller. When I set it the controller leaves power to the cooling plug on until it reaches the set point, which in the case of trying to reach 0C is probably forever. I'm sure I could plug the refrigerator straight into the wall and it would have the same short cycle issues.

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Old 01-10-2013, 02:54 AM   #8
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Quote:
Originally Posted by mj_b90 View Post
After checking the manual 7 is the coldest setting so that can't be it. But setting it to 1, 4, or 7 didn't seem to make much difference to the timing. Is it possible that the compressor is overheating and cutting out until it cools down?
I'm measuring temp with the probe in a beer bottle filled with water and it seems to have bottomed out at 5C and holding there. Could it be that this fridge won't get down much lower than that?
I know this thread is few months old so not sure if you found a solution to your fridge or not. I also have a haier mini fridge I turned into a fermentation chamber and was having a similar problem, my solution was a probe or thermocouple under the cooling coils covered by a piece of plastic. I removed the plastic piece and moved the thermocouple away from the cooling coils. I have got it down to 0 degrees since doing this.
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Old 01-10-2013, 03:46 AM   #9
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Another option is to bypass the built-in thermostat entirely. Usually, near the compressor, there's a plastic enclosure. OPen that and you can see where the thermostat ties in to the mains and the overload protection/start relay for the compressor.

On my fridge, the thermostat was wired in series with the overload protection module. I just disconnected the two wires for the thermostat, then connected the wire that went in to the the thermostat to the the free connection on the overload protection module. Now the fridge will run as long as my external temp controller requires.

The only downfall here is that you now are relying solely on your external controller. If it fails in some way and gives continuous power to the fridge, the fridge can burn out. Make sure your relays in your controller -- mechanical or SSR -- will always fail open.

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