Trouble with Glycol Fermenter

I built a glycol fermenter from the design given in BYO's "25 great homebrew projects" issue. The design is to put the cooling coil of a window A/C unit into a glycol bath (I used RV antifreeze), and fountain pumps to circulate the cold glycol through copper tubing surrounding two fermenters. Finally, Love controllers run the fountain pumps and A/C unit to ensure that the glycol bath and both fermenters stay at the correct temperatures.

It ran great for the first three batches. I then had some house guests, didn't brew for a month, and tonight powered it back up. It didn't cool the glycol bath -- after an hour of the A/C unit running it had cooled by two degrees. (Everything was on and running -- the fan was running, compressor got hot, etc. Just that the hot air that should have been blowing out the back wasn't, and the coil didn't get cold.)

I've got a couple guesses about the problem. Could be that during the process of moving the A/C coil from inside the unit to outside, I damaged the tubing in a way that is imperceptible to the eye but allowed the refrigerant to escape.

Or, I might have damaged the A/C unit in some other way.

Could be that RV antifreeze damaged the coils, though it's just propylene glycol, water, and some chemicals designed to make it less corrosive.

I'm curious if anyone else has had issues with this design, or might have some insight into this problem.

i'd guess that you lost the refrigerant. Time to find another Ac unit.

OR, just find a decent refrigeration repair shop and have them top off the refrigerant. I found
one that really looks forward to the 6 pack of homebrew I bring along; fast/cheap repair.

Can window AC units be refilled?

Yes, any air conditioning or heat pump system can be refilled. I had service valves ($15) installed on
my chiller, they will expedite (faster/lower coast) future service. I have a small chiller hooked to a
liquid fermentation chamber. About every 3 years, I can tell it takes a little longer for it to maintain
lager temps. During the winter (less busy), I get the refrigerant refilled and it runs like new again. On
my small chiller, the refrigerant quantity is weighed; so they need to evacuate (pump out)the remaining
refrigerant and then pump in the appropriate amount of refrigerant. That service has always taken less
time than consuming a six pack.