Lunkhead goes external temp control+calibrate your Danby temp sensor.

[lunkhead]

I finally grew tired of fighting the defrost cycle on my Danby DKC645 so I found a Johnson Controls model A19ABC-24C temp controller on line for 32.50 + 5.00 shipping and installed it a couple days ago. Been testing it the last couple of days with a 2.5 gal bucket of water and is working great. have it set for 35 deg on the dial and it kicks the compressor on at 39 deg and off at 34 deg, a 5 deg diff, which is what I have it set for. Water temp in the bucket is 36.5 deg, right smack dab in the middle.

I also decided to see if I could calibrate the temp sensor reading on this thing, it's there, might as well see if it can be made useful. I cut the 33k resistor out and dunked the sensor into an ice water bath with my calibrated round dial thermometer and waited about 15 minutes for the readings to stabilize. The round dial read 32 deg (good, it's still accurate) and the Danby display read 30 deg. Humm, might be these things just won't get cold enough. From my previous research with the 33k mod it would appear I need parallel resistance but 33k is too low, raised the reading to 35 deg, I only need to come up to 32. I started out with a 220k and the reading came up to 32deg. (IMPORTANT NOTE: the reading does not change instantly, takes about 5 minutes) I tried several values from 82k to 560k to try and find the center of the reading. On my unit (don't know if yours will act the same) anything below 100k or anything above 390k would move it above or below 32deg on the display. Measuring the voltage across the sensor, with 100k volts was 2.79vdc, with 390k volts was 2.84vdc. It looks like 2.81vdc is pretty close to center at 32 deg. The 220k that I started with gave me 2.83vdc, a little high. It looks like a 145k would do the job, but that's an odd value I don't have lying around, but I do have lots of 150k resistors, so I used that. 2.81vdc, right where it needs to be. (Please note that this takes some time to do as the readings on the danby temp display don't change instantly, keep the ice bath up and I had my round dial in it the whole time to insure 32 deg temp) So how is it at a higher temp?? I grabbed the 2.5 gal bucket of water, which by now should have warmed up a little, and in went the sensor and round dial. Waited about 15 minutes and stirred the bucket a few times, both readings were 43 degrees!!! Glad to see that. Just for fun I put an old red mercury looking thermometer that I use to keep track of the basement temp in the bucket and it came in at just a tad under the 44 line. So I put it into the ice bath and it read about 32.5 deg. It looks like the Danby display temp is now pretty accurate, at least from 32 to 43 degrees (BEER TEMP) and maybe/hopefully a few degrees below and above 32 - 43.

Other thoughts, using the 150k instead of the 33k will lower the danby temp 2 deg instead of 6 deg. Perhaps using 150k and moving the sensor to the top front of the danby (suggested in previous posts) will give better temp results, if anyone would like to try, but there is still the dreaded (at least to me) defrost cycle. The 150k would just go in place of the 33k, same hook up, in parallel.

[cubby_swans]

Dude, you should work for Danby. It's amazing what a little time and a 50 cent part can do to fix what amounts to simple poor design and inattention to detail. It's quite certain that the Danby hardware is capable of performing, they just didn't take time to make sure the stuff that controls that hardware controls it properly. Like buying a new car with a bad computer chip in it.

So, what I'm gathering from all this is that, while a 33k resistor makes the Danby get much colder, you don't need it anymore since you have an external temp controller. HOWEVER, the 150K resistor makes the Danby display an accurate temperature on it's blue display, and theoretically, by itself, should allow the Danby to cool itself an additional 2 degrees.

I'm unsure if my display is inaccurate or not. I have mine set to 36, and it swings between 37 and 34, and a temp reading of a glass of water sitting in the kegerator reads 36.5. (glass of water sitting right next to the cold plate). When I pour a few glasses of beer, the last beer reads 39.5. So I'm wondering if the temp sensor is also off a few degrees and by adding a 150K resistor, I might get my beer down to 38 where I'd like it. I think I'm going to get a resistor tonight and give it a whack.

[psychodad]

Interesting that it takes that long to see a change on the display. I was going to add a pot to mine and try to dial in on the display against a known measured temperature but your findings suggests that won't work. Or at least it will take a bit of trial and error to get it to match.

I took some vacation a week or so ago (use it or lose it) and intended to diagram the control board to see what it would take to get rid of the defrost cycle or at least make it not occur as often. I was also going to tie the output for the fan high all the time and use it to move air to the tower but I drank dunkleweizen instead.

One thing that you will find you can do now that you have an external temp control is set the Danby control to the highest setting and let the fan run pretty much all the time except for the time it wants to defrost.

[lunkhead]

Originally Posted by cubby_swans

Dude, you should work for Danby. It's amazing what a little time and a 50 cent part can do to fix what amounts to simple poor design and inattention to detail. It's quite certain that the Danby hardware is capable of performing, they just didn't take time to make sure the stuff that controls that hardware controls it properly. Like buying a new car with a bad computer chip in it.

So, what I'm gathering from all this is that, while a 33k resistor makes the Danby get much colder, you don't need it anymore since you have an external temp controller. HOWEVER, the 150K resistor makes the Danby display an accurate temperature on it's blue display, and theoretically, by itself, should allow the Danby to cool itself an additional 2 degrees.

I'm unsure if my display is inaccurate or not. I have mine set to 36, and it swings between 37 and 34, and a temp reading of a glass of water sitting in the kegerator reads 36.5. (glass of water sitting right next to the cold plate). When I pour a few glasses of beer, the last beer reads 39.5. So I'm wondering if the temp sensor is also off a few degrees and by adding a 150K resistor, I might get my beer down to 38 where I'd like it. I think I'm going to get a resistor tonight and give it a whack.

If you have done no other mods to your danby than adding the 150k should give you a 2 deg temp drop. When you do it, try putting the sensor in an ice water bath and see if it will read 32 after 15 minutes or so. The sensor looks pretty water proof and mine is none the worse for wear after being dunked for over an hour. I think if you moved your glass of water away from the cold plate the temp of the water will rise.

[lunkhead]

Originally Posted by psychodad

Interesting that it takes that long to see a change on the display. I was going to add a pot to mine and try to dial in on the display against a known measured temperature but your findings suggests that won't work. Or at least it will take a bit of trial and error to get it to match.

I took some vacation a week or so ago (use it or lose it) and intended to diagram the control board to see what it would take to get rid of the defrost cycle or at least make it not occur as often. I was also going to tie the output for the fan high all the time and use it to move air to the tower but I drank dunkleweizen instead.

One thing that you will find you can do now that you have an external temp control is set the Danby control to the highest setting and let the fan run pretty much all the time except for the time it wants to defrost.

Yes I was surprised myself that it took that long to change. The thermistor that is the temp sensor responds pretty quick to temp changes, but danby must have built a slow hysteresis into the system to keep it from rapid cycling. I do keep the danby control at its highest setting, but long since pulled their little fan out. But it sounds like a good idea to put it back in, a little extra air movement should be a good thing. I did not pull the top off to install the new control either, just took the little cover off over the compressor and spliced the wires in there. Mounted the control to a piece of trim board I had, attached to the back of the unit. Also put 2 indicator lamps on it, 1 red for compressor off, 1 green for compressor on. One thing about these danbys they do run quiet, so now I can see what it's doing.