It is always great being a tinkerer and someone else enlists your skills for their projects. Then you still get to tinker and make things, but you can do it with “their” money. 😀 Life can’t get better unless beer was free and didn’t get warm. Such a thing happened this year as my buddy Kevin and I were talking about how it was so warm last year and we didn’t kill any deer early because we self butcher. When it is warm you have to break the deer down to buckets in the fridge fast and that is a lot of work just after you tracked and dragged a deer out. Kevin said “Let’s build a cooler” and we started on design.
I am not going to go much into building the cooler frame as its just 2×4’s on pressure treated landscape timbers with a stone floor built under his shed roof off his outbuilding. Kevin bought the 2×4’s, I had almost all the R13 insulation left over from my garage refinishing, we got a free exterior door from another buddy and he got a deal on 1/4″ plywood on Facebook marketplace. Then he bought a cheap used air conditioner and we built what you see here with a hole for the air conditioner.
Kevin saw the price of the Coolbot controller at over $300 and texted me to assign my engineering resources to perform this task as a more cost effective price range. I did my research and told him to buy the Inkbird controller for $16 and to get the mounting box for under $24 total for both. I told him I could make it work with it. This would control the compressor and when you switch the air conditioner on the fan runs 24/7 and the inkbird tell the compressor when to turn on and off. Below you can see the final setup and the inkbird is on the far right. It and the air conditioner was all we started with. The Inkbird is set to run until 40° and this was just taken when the unit was off. The Silver box was added later for the failure you’re about to read about.
So initial tests seemed to work and we got the room down to 50° in a few hours. The coil was icing but everything seemed to be OK. Then in the beginning of October my daughter shot a doe. Everyone is cheering, she got a deer and a real test for the cooler. We hang the deer, start the cooler and have some beers and watch the cooler. It looks good and Kevin goes out and checks it before bed. Its only down to high 40’s and iced, but its running. He wakes up Sunday and it tripped the GFI from being over loaded, ice dripping or something and working too hard and its 55° in the room. The deer is cold still, but it is time to eat eggs fast and start butchering.
That was a failure because the freezing coil is straining the compressor. The air conditioner is not designed to be a cooler at 40°. So I had to figure out how to keep it from freezing up the same was a Coolbot does. So I looked around and found a Johnson Controls A19ABA-40C temperature sensor that would work. It would have closed contacts and open on freeze so it could turn the compressor off when the coils froze up. Then when the compressor is off and resting the partially frozen coils are being defrosted by the running fan and still cooling the air in the cooler.
This was set to about 30° with about a 8° temperature differential. So when the coils reached 38° the compressor would turn back on.
As you can see here I used the existing sensor mount and inserted our freeze sensor to lay flat on the coil. I had to bend the tip a few times to get it just correct to lay with light pressure against the coils.
Here is the wiring diagram. Most heat pumps and air conditions use the standard color of yellow for the activation wire for the compressor or pump start. I cut the yellow wire and inserted our controls instead of the existing control sensor.
As you can see when you start it the Inkbird contact will close, or will already be closed because its warm in the cooler. When it gets to 40° this contact will open and stop the compressor. When you first start it the units compressors works overtime trying to cool the room. When the coil freezes the compressor is running for nothing. The freeze sensor senses this and will open its contact letting the compressor, take a break until the coils melt out.
We ran a test like this for over 24 hours and you could hear the compressor turning on and off occasionally as needed. Some ice was on the coils, but it worked perfectly and we maintained 39° – 40° all the time.
Now you too could Redneck engineer a Coolbot on your own. The Coolbot sells for the cheapest I have seen for about $330 and I think we have less than that in the entire cooler.