Diagnosing my new-to-me minifridge kegerator

[htims05]

I started posting in the thread about the course adjustment screw on thermostats but I was getting off topic so I started my own separate thread here.

I picked up a 5.0 cuft minifridge the other day cheap. Fits 2 corny kegs, 5lb co2, with no mods to boot other than raising the t-stat knob up about 2 in (the capillary tube is in the same spot though). I was going to use it as cold crash or maybe a ferm chamber

It currently has 1 full corny, 1 empty corny and the co2 in it. I'm thinking something's wrong with it (t-stat) as it cycles about every 15 min and only cools to ~45f (the kegs and co2 have been in it for 24hrs). The compressor reaches 160f when the ambient temp is 85f (its in my garage).

It seems to constantly get colder - I have the t-stat set to max cold but the short cycle is very odd to me. My other minifridge kegerator that only has 2 kegs in it (external co2) cycles about every hour for 45min run time (using an inkbird but the t-stat on that one is still installed).

Attached is a graph of the temperature over the last 24 hours. The sensor for this graph was sitting on top of a keg, this morning (big drop in the graph, other spikes are door openings) I put it on the floor of the fridge (there's like a 5f degree difference in 20in of height - maybe I just need a fan in there?).

Thoughts - issues? I plan on bypassing the t-stat and going with an inkbird this weekend...but still seems odd to me.

 

[etk29321]

I used to have a ‘high efficiency’ room ac unit that showed similar behavior. It had a digital control board that seemed to artificially limit how long the compressor was allowed to stay on — to the point it couldn’t cool a room effectively. Fixing it required bypassing the control board and putting in my own temp probe ( this was pre inkbird dats, but same idea). After that it worked great for many years.

 

[htims05]

I used to have a ‘high efficiency’ room ac unit that showed similar behavior. It had a digital control board that seemed to artificially limit how long the compressor was allowed to stay on — to the point it couldn’t cool a room effectively. Fixing it required bypassing the control board and putting in my own temp probe ( this was pre inkbird dats, but same idea). After that it worked great for many years.

Interesting...although I don't think this is a "high efficiency" mini fridge (ha - that's like an oxymoron right). It's some old thing - Oster brand and just googling the model number returns like no results...it might pre-date the internet. I have a feeling the t-stat is bad or that's just how it was designed to work for some reason.

 

[NBBrewer]

Hitman how did you get a graph of the temperature in your kegerator. Its a case of I want that.
NBBrewer

 

[htims05]

Hitman how did you get a graph of the temperature in your kegerator. Its a case of I want that.
NBBrewer

I have a weather station out back that’s connected to my irrigation so it limits watering if it rains. It has the ability to add additional remote temperature and humidity sensors...I throw one in the kegerator.

ambientweather.com

 

[NBBrewer]

I have a weather station out back that’s connected to my irrigation so it limits watering if it rains. It has the ability to add additional remote temperature and humidity sensors...I throw one in the kegerator.

ambientweather.com

Nice. Sounds expensive or did you do a little DIY wiring to a cheap one?

 

[day_trippr]

That temperature plot is definitely recommending a fan running 24/7 be added to keep the cabinet temperature equalized top-to-bottom.
Otherwise the behavior may be the nature of that particular fridge. I have read of many new units from manufacturers that seem to have an opinion on how cold a beverage dispenser needs to get and they typically had a temperature floor around 40°F...

Cheers!

 

[htims05]

That temperature plot is definitely recommending a fan running 24/7 be added to keep the cabinet temperature equalized top-to-bottom.
Otherwise the behavior may be the nature of that particular fridge. I have read of many new units from manufacturers that seem to have an opinion on how cold a beverage dispenser needs to get and they typically had a temperature floor around 40°F...

Cheers!

I just bypassed the internal thermostat and it dropped the empty chest down to 30f in about 45 min (from 77f) and it didn’t cycle and the compressor temp didn’t go over 160f (infrared thermo).

So now it’s hooked up to an inkbird with the probe strapped to a coke can (probe insulated) sitting on the hump. CO2 tank in the middle of the hump and a muffin fan on the other side of the hump blowing upward.

new chart forthcoming....couple days.

 

[day_trippr]

Sounds good...

Cheers!

 

[htims05]

Seems to be much better now when I let the inkbird do everything. I think the t-stat was either bad or setup to only chill so far...I'm thinking it was bad as it was hitting the setpoint in 15min. I'm at 1 hour between peaks now, with inkbird set to 38f, 3deg differential, 10min compressor lockout, and a muffin fan 24/7 which is the same on my other minifridge and I'm getting similar wave chart (other mini fridge doesn't have a CO2 tank in it so there's much more airflow.