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By NightRaider
Posts:  414
Joined:  Mon Jun 07, 2021 4:01 am
Today's my forumiversary, so I wanted to go ahead and post a writeup on the progress I've made on a project I hinted at a month ago. This cooling method revolves around the idea of harnessing the power of a standard window AC unit to effectively make an extremely powerful water chiller for (probably) cheaper than one would cost to buy outright. This method was inspired by this little-known tutorial, but with my own spin added in the later stages. I believe this should work well for glass terrariums as well as moderate-sized areas with some level of insulation because it's designed to be extremely scalable. For instance, I plan on using it to attempt to cool a section of a cabinet measuring roughly 30"x22"x17" (~48 gallons) with a 240mm PC radiator, but you could easily get a larger radiator or likely even chain multiple together for larger areas. You could even get more cooling power by using a larger AC unit and cooler, or by mixing food-grade glycol in with your water to cool your reservoir below freezing. FULL DISCLOSURE: I have NOT yet tested this to see just how well it performs as my testing area isn't fully enclosed yet, BUT both the water reservoir and the radiator surface cools from 72° to under 40° within 20 minutes. The only drawbacks I've noticed so far are obviously the noise of the AC unit (though it doesn't have to run very much), the copper tubes in the unit will frost up from condensation when running and then drip a bit after the unit kicks off, the system puts off a decent amount of heat and will need some ventilation, and the whole assembly is pretty bulky and not easy to move without damaging it unless you mount it all on a base of some sort.

Required Materials
~5000 BTU A/C unit w/ manual controls – But find a cheap used one instead, shouldn't be hard to locate one.
Cooler (~28qt or 15in+ interior width cooler) - Again, should be able to find one used on the cheap. Mine was like $8 from a pawn shop.
Aquarium pump – this model was probably overpowered, you could probably go with a lower GPH model depending how high you're sending the water.
240mm PC water cooling radiator – As mentioned, this part scales so you can go larger or use more than one if you want. Needs to have studs that fit 3/8" ID tubing.
(2) 120mm PC fans (for 1x240mm radiator) + PC fan power supply + PC fan splitter(s) - Just match this to your radiator.
3/8” ID - ½” OD vinyl tubing
90° elbows for tubing + (4) #4 hose clamps Not strictly required but makes for cleaner mounting. Again, match to your radiator setup.
Phillips Screwdriver
Drill and ½” bit
1¼” hole saw - size needed for plug on pump linked, may be slightly different if using a different one.
Saw (Jigsaw, Sawzall, most hand saws, etc) - Literally anything that can cut the cooler wall. I used a jigsaw with a long blade.
Pliers (recommended) - makes pulling the knobs off easier
Ratchet and socket set - probably want long sockets for this
Duct tape
Great Stuff spray foam insulation - Pond and Stone preferred but nearly impossible to find right now
Flex Seal spray
Heat gun or hair dryer (optional) - not required but makes life easier
Latex gloves (recommended)

Time to Complete
~2-4 hours + 12 hours foam cure time + 48 hours Flex Seal cure time

Step 1
TEST THE UNIT BEFORE STARTING. Especially if you got it used. I completely forgot to do this until I was nearly done, and while mine did work I wouldn't have been very happy if it hadn’t. Just plug it in a minute and make sure it cools first before proceeding.
1.1 Starting.jpg
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Step 2
Set knobs to max cooling (lowest temperature) and low fan speed (low cool), and remove rails and fins if attached.
2.1 Rails+Fins Removed.jpg
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Step 3
Remove the knobs using pliers if you have them, remove the filter and any screws holding the front panel on, then remove the front panel by carefully prying the tabs on sides loose.
3.1 Front Panel Removed.jpg
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Step 4
Remove all screws holding metal enclosure (but not the base) on, remove cover.
4.1 Cover Removed.jpg
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Step 5
Remove the Styrofoam cover from the top of the fan behind the front panel heat exchanger, remove the screws holding on the heat exchanger behind front panel, then remove the nut from the fan rod using a ratchet and long socket (mine was 8mm).
5.1 Fan Nut.jpg
5.1 Fan Nut.jpg (647.6 KiB) Viewed 4582 times
Step 6
Be EXTREMELY careful here, I can't stress this enough. First, very gently lift up on the metal heat exchanger to allow the Styrofoam piece underneath to lift up above the lip of the bottom panel and be removed, which in turn will allow the fan to be pulled forward and removed. The control box may need to be unscrewed from the base and moved aside, as well. If any of the copper tubes running to the heat exchanger are damaged during this process, the entire unit will be completely scrapped. Note: This step can be simplified by just destroying the Styrofoam, as it won’t be needed later.
6.1 Fan Removed.jpg
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Step 7
Most important step here. Fully detach the control box from the heat exchanger, including all wires and temperature probe which can just be bent out of the way indefinitely. Then extremely carefully bend the copper tubing leading to the heat exchanger so that it sits forward of the unit by just enough to clear the cooler wall thickness. Again, be extremely careful not to damage the tubing as that will let the refrigerant leak out making the unit worthless. On my unit the tubes had some kind of hard plaster attached to them, if this is present then you can carefully break it off.
7.1 Controls Detached.jpg
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7.2 HE Moved Forward.jpg
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7.3 Random Plaster.jpg
7.3 Random Plaster.jpg (606.41 KiB) Viewed 4582 times
Step 8
These next couple of steps will be pretty messy so make sure to have a vacuum on standby. First, line up your cooler in line with the AC unit as it will be installed (front or either side works here), then with a sharpie make a mark on the cooler in front of the copper tubes where they’ll need to pass through the cooler wall. Then, cut the slot out going upwards towards the cooler lid. I started by drilling the bottom out with a ½” bit then cut the rest with a jigsaw, but you can do this any number of ways.
8.1 Aligning With Cooler.jpg
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8.2 Marked and Started.jpg
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8.3 Slot Cut.jpg
8.3 Slot Cut.jpg (764.24 KiB) Viewed 4582 times
Step 9
Next, drill 3 holes in the lid: use the ½” drill bit to make 2 holes to run tubing in and out – you may need to wobble the bit some for the tubing to fully fit through – then make 1 more hole with a 1 ¼” hole saw or larger to fit the power plug for the pump.
9.1 Lid Holes - Bad Pic.JPG
9.1 Lid Holes - Bad Pic.JPG (202.29 KiB) Viewed 4582 times
Step 10
Thoroughly vacuum out the inside of the cooler, then lift the AC unit and slide the tubing down into the slot in the cooler so that the heat exchanger is sitting inside the cooler. You may want to reattach the control box back before moving the unit during this step.
10.1 HE Mounted In Cooler.jpg
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Step 11
Wrap duct tape very thoroughly around the tubing and up both the inner and outer walls to cover the slot, leaving the top open for now. Slowly fill the gap with spray foam, starting at the very bottom and working your way up. Wrap a piece of tape across the very top at the end. Let cure for at least 8 hours before proceeding. NOTE: Wear disposable gloves and clothes you don’t care about for this step. If you’ve never used this stuff before, it is EXTREMELY sticky and will literally never come off if it gets on your clothes.
11.1 Outside Taped.jpg
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11.2 Inside Taped.jpg
11.2 Inside Taped.jpg (473.52 KiB) Viewed 4582 times
Step 12
After letting the foam cure, use Flex Seal spray to thoroughly coat the inside of the cooler where taped to fill any remaining gaps or cracks and help seal the tape edges. Let this fully cure for 48 hours before proceeding to Step 13.
Step 12.5 (if needed)
If you got your AC unit used, at this point you can move the fan assembly over to vacuum up any debris underneath and check the rear radiator for lint or debris. If yours, like mine, had a large amount of debris underneath the fan, do yourself a favor and don’t skip this step and clean it out as best you can before powering the unit on, or else you’ll risk that debris being thoroughly redistributed around your work area. Fan assembly removal should be simple – mine only required 4 screws - 2 top, 2 side - to be removed before being able to lift it up to clear the slot on the side of the rear radiator. Just reattach it when done.
12.5.1 Bottom Screws.jpg
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12.5.1 Side Screws.jpg
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12.5.3 Fan Removed.jpg
12.5.3 Fan Removed.jpg (624.21 KiB) Viewed 4582 times
Step 13
Run a length of tubing down through one of the holes from the top of the lid, then attach to the pump. This will be your cool water line going to the radiator, so make sure the tube is long enough to reach where the radiator will be mounted in the enclosure. Place the pump in the bottom of the cooler with the intake preferably facing the heat exchanger, then run the pump’s power cable out through the hole in the lid. Note: If, like mine, your pump only comes with a ½” fitting, you can use a hair dryer or heat gun to soften the end of the tubing enough to slide over the fitting. Alternatively, you can soak the end of the hose in boiling water to soften it.
13.1 Pump Hose Attached.jpg
13.1 Pump Hose Attached.jpg (469.9 KiB) Viewed 4582 times
13.2 Pump Placement.jpg
13.2 Pump Placement.jpg (458.74 KiB) Viewed 4582 times
Step 14
Run a second length of tubing down into the cooler with the end below the expected water level, ideally away from the pump intake. This will be the return line from the radiator, so it should be just slightly longer than the other line.
Step 15
Mount the radiator as desired, then attach ends of both tubes to the radiator. If you're using the 90° elbows, cut two 1.5" or longer pieces of hose off from a scrap piece and attach the elbows with hose clamps. Attach the 120mm fans to the radiator, plug them into a splitter, then plug the splitter into the fan power supply. Move the cooler and AC unit into place.
15.1 Hoses Attached.PNG
15.1 Hoses Attached.PNG (1.07 MiB) Viewed 4582 times
Step 16
Add water until it reaches the bottom of taped area, then slowly add more while checking for leaks until the heat exchanger is mostly submerged. Plug in the AC unit and pump temporarily to make sure everything works.
Last edited by NightRaider on Mon Jun 06, 2022 3:02 pm, edited 1 time in total.
specialkayme liked this
User avatar
By NightRaider
Posts:  414
Joined:  Mon Jun 07, 2021 4:01 am
At this point, things can be as simple or as complicated as you want depending on how you choose to implement your timers and thermostats. I’ll describe a couple methods here, but you can implement this however you want. The main goals are generally as follows: 1) Ensure water reservoir in cooler stays cold but still above freezing, 2) Only run the system at night or when the lights are off, 3) Only run the pump when the terrarium temperature is above the target temperature.

Method 1 (easiest but least control)
For people who just want to buy stuff, plug it in and go, this is the method you’ll want. Temperature logging and alerts won’t be possible though, nor will you be able to set your temperature threshold between turning on and off unless you use fairly expensive thermostats.

Required Materials
2 cooling thermostats – must maintain settings on power loss and be rated for more amps/wattage than your AC unit. Waterproof probe preferable for 1 of these.
Timer or Smart plug
Power strip or Outlet splitter

Step 1
Plug the power strip or splitter into the timer, and set the timer or smart plug’s schedule to turn on at night and off in the morning – generally matching your grow light schedule.
Step 2
Plug in one thermostat, set the temperature to the target low temperature of the terrarium, place the probe in the terrarium away from the radiator, then plug the pump into the thermostat.
Step 3
Plug in the other thermostat, setting its temperature to between ~35 and your terrarium’s target temperature. This can be adjusted as needed to provide a slower cooling curve at night or to prevent the AC unit from kicking on more often than needed – generally you’ll want to try to balance these two. Finally, place the end of the probe into the water in the cooler and plug the AC unit into the thermostat.

Method 2 (more complicated but allows for logging and more control)
For Method 1, ideally for the cooler reservoir thermostat you would use a Sonoff TH10/16 with a waterproof DS18B20 temperature probe as most thermostats’ probes aren’t rated to be continuously submerged. This would also allow for integration with Home Assistant for data logging and specific temperature on/off triggers, which this method revolves around. However, these units have recently been discontinued and their replacement model hasn’t been released yet, which means they’re basically impossible to find currently, so this method can’t really be done right now. Nevertheless, I’ll leave this writeup here as it’s a simpler way of doing 90% of what Method 3 allows. The instructions obviously aren’t the same, but you should be able to figure out how to adapt it pretty easily.

Method 3 (most complicated but fully independent and most flexible)
Coming soon. Want to fully test this for a bit first before linking any code here.
User avatar
By specialkayme
Posts:  291
Joined:  Tue Apr 13, 2021 11:02 am
A) Thanks for doing the write up. Very much appreciated.

B) These builds are very common in the homebrew community to chill beer to fermentation temperatures. They're called "glycol chillers." Homebrewer's are notorious DIYers, so there's a ton of writeups on it. ... 5-1&ia=web

C) Add food grade glycol to the reservoir, not antifreeze. That way everything doesn't die if you get some sort of leak. There are optimal ratios in some of those links above.

D) For those not inclined to build, you can buy them. They're all roughly $1,000 ( ... iller.html), although the "budget brands" are about $700 ( ... iller.html). You can build them for $100 or so (depending on the cost of the window AC unit), although they won't look as neat (although it could look neater

Personally, I'm waiting till I have the space and I'll buy one. One port will be used to chill beer, and one port will be used to chill my highland grow chamber :)
User avatar
By NightRaider
Posts:  414
Joined:  Mon Jun 07, 2021 4:01 am
specialkayme wrote:A) Thanks for doing the write up. Very much appreciated.

B) These builds are very common in the homebrew community to chill beer to fermentation temperatures. They're called "glycol chillers." Homebrewer's are notorious DIYers, so there's a ton of writeups on it. ... 5-1&ia=web

C) Add food grade glycol to the reservoir, not antifreeze. That way everything doesn't die if you get some sort of leak. There are optimal ratios in some of those links above.
Thanks for the feedback, I appreciate it.
B)I actually did run into a handful of these when I was looking around for a better tutorial, but I still couldn’t find a step-by-step one I really liked so I just went ahead and made this after I figured it out. Mine probably ended up a little different regardless though.
C)Doh. I knew that, so I have no idea why I wrote that other than it being 4am when I did. I’ll fix it in the post.
specialkayme liked this
User avatar
By NightRaider
Posts:  414
Joined:  Mon Jun 07, 2021 4:01 am
Adding some observations now that I've had it running for a week or so.

1. As expected, one or more fans are a requirement to pull air through the radiator in order to cool the area. I mounted mine ~3/4" off the surface of the radiator using the long screws included with the radiator as well as scrap pieces of tubing on 2 opposite corners of each fan for stability.
2. Unexpectedly, having a humidifier running as well seems to be a near-requirement. I'm not entirely sure why that is, but just now with the humidifier line blocked it struggled to cool to 65.6 but after clearing the line, it resumed dropping ~1 degree/minute.
3. It's not a huge surprise, but it does still result in a humidity drop, though it can be managed. It works out well with #2 considering having a humidifier running both increases its effectiveness as well as helps negate the downside. More on this in the next couple points.
4. I think I actually could've managed with a single-fan 120mm radiator for my ~50 gallon space. Initially, I was dropping down below 80%H when the pump kicked on, though there were a couple ways to mitigate that. That leads me to:
5. When I first set it up, I was aiming for my reservoir to be just above freezing to provide maximum cooling. However, I believe that the resulting temperature differential between the radiator and the ambient air in the enclosure was what caused condensation to form more heavily and drop humidity. Due to that, I'm now keeping my reservoir roughly in the mid-to-low 40s - though I'm still tweaking it some. This has reduced the humidity drop to more like 85% which to me is entirely acceptable.
6. As mentioned in #4, I think a smaller radiator could have helped reduce the humidity drop while still hitting my current target temp of 62. However, another method to mitigate it could also be reducing the fan amount or speed. For instance, disabling one of the two 240mm radiator fans at night, adding a fan speed controller to one or both fans and lowering the speed, or removing a fan entirely and potentially placing it elsewhere in the enclosure.

Miscellaneous other notes:
1. Even with 3/4" wood on 5 sides and an additional layer of 3/4" foam board insulation on 3 sides, it still seems it could do with more insulation due to how often the pump kicks on. Obviously this is affected by several factors though. For example, when I had my target low temp set to 66 degrees it rarely had to kick on, but dropping that to 62 has caused it to run very often.
2. Plenty of ventilation is needed around the AC unit as it generates a lot of heat. However, I expect this can be mitigated by reducing the difference between the target temperature and the threshold temp when it kicks on, which should reduce the amount of time it runs at once and give the heat a chance to dissipate before it kicks back on.
3. Oddly, 2 different fan power supplies I've tried have stopped working when the temperature rises due to the AC unit running. Of course, this means the cooling in the enclosure fails since the radiator can no longer, well, radiate. Both were rated for a 1a draw, but I saw one other on amazon that was rated for 3a and seemed more robust that I may have to try instead. Obviously this won't matter if your fan power supply is isolated from the heat generated by the AC unit, but still just something I noticed and to be aware of.

I'm finally finished with the entire cabinet and cooling system now, so once I have my settings tuned in and everything running and maintaining temperatures as expected for a few days without any intervention I'll update again with some graphs and code. I'd be lying if I said it was the miracle solution I was hoping for, but so far its still been perfectly serviceable despite its quirks.
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