Hi there,
I see lots of issues. Sorry, I spend about most of sept/oct/nov at brewing festivals infront of a magic box, and there are a few things to note;
* water is bad. Warm beer goes in, cold beer comes out. Ice melts, the more it melts the worse the box works. Water is also a poor conductor unlike glycol, having it run through a water bath in a fridge with a static household fridges will be heavy going if you pour more than a few pints.
* coils vs plates - plates work much better. Not all plates are made equal, there are soda plates with about 6 feet of coil, per the micro matic part you need at least 15-18 feet
* ambient temps change - sounds silly but the higher the temp the more head pressure required to stop the gas coming out of solution and cups of foam. But there is a maximum, get over the 30's, where you need more than 220 odd kpa and your bound for trouble. Easy solution, have the keg in the fridge. Constant temp and constant pouring.
Easiest way, keg in fridge.
Scotty