just about done with my fermentation chamber

ive built a box around a mini fridge, insulated with 2 inch foam insulation. Its all together now and temp controlled with a johnson controller. I turned it on tonight and it went from 75 to 42 in about 2 hours. I just cut it off and will see what the temperature is in the morning. Is there any good way to determine how efficient it is? It was at 42 degrees for about 15 minutes, so it seemed to have kind of stalled. Think it will have problems getting to 34 degrees? I plan on using it for fermentation and crash cooling and the occasional lager. i didnt feel any cool spots around the outside of the fermentation chamber. Do i need to mount fans in the chamber to keep the air moving around?

also, are the johnson temperature controller nodes (i think thats the right word) water proof? Id like to keep it submerged in liquid to get a better idea of the temperature inside.

Ill get some pictures and post tomorrow.

my fermentation chamber measure 41 inches long, 26 inches wide, 29 inches tall on the inside.

This morning when i checked the fridge it was 3 degrees below ambient temperature. It did not keep temperature well over night, but not sure if this is expected or not. Before i left for work at 830, i set the fermentation chamber to 35 degrees. When i got home at 6 it was at 44 degrees. Seems like its having a hard time getting down as far as i would like to crash cool. The fridge i am using is a sanyo, just like this one:

http://www.amazon.com/dp/B000260JRG/?tag=skimlinks_replacement-20

i didnt realize it was so expensive, i got it for free.

i dont currently have any fans on the inside, think that would help? or think there is a flaw in my design?

The stock temperature probes from Johnson are not entirely waterproof. I put mine partially submerged in a gallon jug full of water after wrapping it tightly in a plastic bag. They're a bit delicate.

As far as your temp control issues are concerned, look at a few things:

1. the cooling power of the minifridge vs. the cubic footage of your chamber

2. any and all air leaks. When I built my chamber, I had a lot of little holes to fill with my caulk. Also get some aluminum tape if you haven't for the seams in the insulation sheets - that seemed to help mine a lot.

3. if the minifridge won't get it cold enough on a consistent basis, consider ditching it for a spare window AC unit. I've got one of those in mine. I started with the intention of using a minifridge's guts, but I ditched it when I realized I'd built something with 40-60 gallon capacity depending on the shape of vessel I used. AC units simply kick ass when it comes to cooling, as long as you can somehow bypass their built in thermostat.

I spray foamed all cracks and seams, then used aluminum tape over it as well. I'm guessing it just doesn't have enough power to keep it below 40. I have the temp controller set to 50 right now and it seems to like that temp better. It actually has a chance to cut off. I'm going to throw a few fans in there this weekend and see if that makes a difference as well. I had wanted to be able to crash cool with this as well but perhaps it just isn't meant to be.

The fans will definitely make a difference, I think.

Keep in mind that having some beer in there with thermal mass will help maintain temps better. Gas loses its thermal energy much faster than liquids or solids. That's why it's generally more accurate to monitor a liquid's temperature in a chamber like that, too, so if you can find a way to safely suspend the temp probe in liquid, it should give you a better concept of how cold your beer is as opposed to the air around it.

I found for myself that once I put the temp probe in some liquid, and later some beer in the chamber, my AC unit quit cycling all the time. I suggest leaving a thermometer in the chamber to measure the general air temperature for a while so you can get a sense of the air vs. liquid temps. I usually notice a 5-10 degree difference, depending on how recently my AC unit cycled. Liquids will warm up more slowly and lose energy more slowly than air, so they will show a different temperature.

If you do these things and it still doesn't help, keep an eye on your fridge's compressor. Constant cycling may burn the thing out more quickly.

Post a pic and it may help pinpoint the problem. Are the sides of the fridge covered with insulation? That's usually where the condenser coils are located and this could interfere with their ability to shed heat.

I'll get a pick tonight. The sides of the fridge are not covered up and are outside of the fermentation area.