Update: Replacement AC unit for my fermentation cabinet

[limulus]

Several months ago, I had to buy a new 5000BTU AC unit for my fermentation cabinet. The cabinet is 4x4x4 and has foam insulation lining the 4 walls, the ceiling and the doors. The floor has about 3.5-in of the blow-in type insulation.

The old AC was a 5000BTU GE unit that I bought brand new and the compressor just stopped working after one season. The new one is an Emerson Quite Kool which is also 5000 BTU.

For this installation, I left the temp probe from the AC inside the cabinet. The old one was gently folded back and extended outside the cabinet and all sealed with Great Stuff. It is controlled with an STC-1000 and the probe is inserted into a thermowell which is screwed into the cap of a 1L bottle of water. The one thing I immediately noticed about this new setup is the fact that the compressor cycles on and off. The old way, the probe was in the hot garage and the compressor stayed on until the STC1000 reached its set point and turned off the AC. I have it set to 20C which is 68F and it cycles on at 21C. To get it back down to 20C, the compressor cycles on and off about 3 times while the fan continues to blow. I believe this is probably better for the unit than a sudden power shut-down while the compressor is running. The AC is allowed to run more like its intended use in this configuration and I don't have to mess with the internal thermostat. BTW, the time between on/off cycles is about 50-min and it runs for about 5min total.

Only time will tell, but I believe leaving the probe inside is going to work better for me.

 

[Stealthcruiser]

Lemme' see if I follow ya':
On the new one, you re- positioned the probe from it's "as installed" location, to outside the air conditioner, yet still in the ferm cabinet?

This probe is hanging in "free air", and in no thermowell nor thermal mass?

The new unit thermostat, set at it's coldest position?

 

[limulus]

Half correct. The probe from the STC1000 is in a thermowell inside a 1L bottle of water.

 

[atoughram]

I've got a 4000 btu unit on a similar sized and insulated ferm. chamber. It is controlled by a Brewpi with a thermowell into my 17gal conical fermenter. I noticed that if I tried cooling too much, the evaporator coils would ice up and the compressor would run continuously. I looked into a coolbot to combat this problem but they are too expensive. I talked to a HVAC guy I know and he told me to install a freezestat - simply another thermostat with the probe in the evaporator - and set it for 32f/0c.

I wired up a STC-1000 for the freezestat and now have no evaporator icing problems.

Was your old unit icing up?

 

[limulus]

No, the old compressor just stopped working. The fan would work, but the compressor never kicked on. So, I cut the cord off and threw it away. I wish there was a way to recycle crap like that.

 

[limulus]

Now after a couple of months, the new AC unit is still working quite well. I'm still running it with the ACs probe inside the cabinet instead of routing it outside. What that does is allow the compressor to cycle on and off a few times during the power-on cycle. With the probe routed into the ambient garage air, which is usually warmer than 68F, the compressor runs until the internal temp reaches the set point and then the STC1000 kills the power.

It is still early, but I think the old way was more stressful on the compressor. The old AC only lasted one season so if this one makes it into next summer, I'll have a better idea about my "theory".