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Old 09-26-2010, 08:47 PM   #1
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Default Controller set point and differential problem

If you have a set point of 45 and a differential of 3 why would you see a temp of 37 on the controller? I assumed with my new Johnson controller it would keep the temperature +/- 3 degrees of 45 but I just walked by and found it at 37. Did I miss a setting?

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Old 09-26-2010, 09:40 PM   #2
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Have you had the freezer open for any period of time?

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Old 09-26-2010, 10:37 PM   #3
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Originally Posted by Naked_Eskimo View Post
Have you had the freezer open for any period of time?
I might have taken a keg out a few minutes before. Maybe I need to let it cycle and check the temps when I know the door is closed.
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Old 09-26-2010, 10:41 PM   #4
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I've found if the door has been open for a lengthy period of time, the temp drops quite a bit. I suspect it is because the probe detects the ambient air (e.g. 70F) and attempts to cool that down...so the cooler is on longer than needed.

I've actually right now just wrapped the probed up in several layers of bubble wrap to make it a little more insensitive to an influx of warmer ambient temperature. Hopefully this works!

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Old 09-26-2010, 11:00 PM   #5
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There can be quite a swing depending on where your sensor is. Some of it is pretty misleading though as the keg temp won't fluctuate like that due to the mass of liquid. As long as it is maintains the right temp once you close it up and it gets a chance to stabilize it is all good.

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Old 09-27-2010, 12:58 AM   #6
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like others have said you can try insulating your probe to prevent temp shocks. Place the probe in water, that will do the trick

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Old 09-27-2010, 02:08 AM   #7
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Now I'm unsure again. I just went to watch TV for a few hours and left the keezer alone the entire time. Looking at the controller now it says 38 degrees.

Why would it keep running until it hit that low a temperature? I assumed that setting it for 45 with +/- 3 would cause it to shut off at 42. I can see it creeping down to 41 or maybe 40 but 38 seems like a bit much. Or is that normal?

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Old 09-27-2010, 02:17 AM   #8
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I have the exact same issue...hopefully someone can solve this for us!

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Old 09-28-2010, 03:12 PM   #9
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it will probably take quite a while for the temp to come back up after hitting 37. did you hear it running at all between when you checked and it was 37 and then when it was 38? i bet it'll just take a while (like a day or so maybe, depending on the keezer) for the temp to creep back up to its normal range. if a cooler can keep ice for days in 90 degrees outside, imagine what your keezer insulation could be capable of in 65-70 ambient temps.

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Old 09-28-2010, 09:19 PM   #10
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Someone mentioned in another thread yesterday another good thought - When your compressor shuts off, there's still a bunch of really cold coolant in the evaporator coils that could well take your keezer down another few degrees.

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What does the primary pressure gauge on the tank tell us? That's right, the temperature. Put it on a scale if you want to know how much is in it...
Put some duct tape over the gauge - Or better yet - Replace the high pressure gauge with a plug - High pressure gauges are useless!
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