window AC for cold room

Systems, Gear, & DIY
1

Got a new (to me) AC for my cold room today.  The old one was just too small, I think.

Anyway, tore the new one open and it has two temp sensors.  One in the duct for the cold air (to the room) and one attached to the coils.

I don’t recall a two sensor thermostat on the other ACs I’ve opened.

I’m going to go ahead and put the cold air thermostat into the can with the light bulb to make it think the room is warmer, but curious about the other stat.

It is, of course, a unit with digital controls unlike my old unit.

Anyone familiar with AC units?

2

That second sensor is most likely there to detect ice build up on the coils and prevent damage to the unit

3

That is exactly my theory.  Just cut the larger opening to put it in the window, so now i’m committed.

4

You may want to look into a coolbot. A buddy of mine tells me they are worth every penny.

5

With the digital ac unit I modified into my glycol chiller i measured the resistance on the thermostat at 2 different temps (like 65 and 85) and have a relay switch between 2 different resistors to trick the unit into thinking it os high or low.

Of course I trashed my ac and voided the warranty, so if you dont want to void the warranty go the coolbot route

6

I’ll see how it goes as is. I don’t need to get down to 35 and the cool it is kind of pricey.

7

You should be able to set the AC as cold as it can be set and attach it to a Johnson/Ranco controller.  The controller will then get it as cold as it can i believe.  Otherwise you can set it to the temp you are looking for via the controller.

8

Yes, but this will only get to 60 which is the lower limit set on the internal AC controls.

The hurdle is apparently the sensor on the coils.  I pulled that and stuck both sensors in the can.  As long as I keep the coils from freezing it seems like it will get as cold as I want it to.

I’ve got the A/C plugged into a timer, so it only runs 15 minutes at a time to avoid icing the coils.  I have no idea how much it is actually running, but it doesn’t seem like much.  The room is mid-50s at the floor, 60 at the ceiling.  I’ll see if I can take the whole room down to 50 but I don’t think I need to go any lower.

This is my ghetto coolbot.  A can to keep the sensors warm, a timer to keep the coils defrosted.

9

I think brewhemoth has instructions to turn an ac into a glycol chiller and part of the process is overriding the built in thermostat.

10

I’ve over-ridden it, but in a way that I can easily restore the AC to it’s intended use.

I just hadn’t seen that second therm on the coils before.  Could be that it was there and I missed it and that’s why my last AC didn’t cool as well as I would have liked, but I think it was undersized anyway.

11

^^^This

Depending on the age of the A/C, that thermostat may kill the compressor allowing the coil to de-ice while the fan still runs. Its not going to cool well in that cycle, but protects the unit. It will work much like the primary thermostat that controls your desired temperature. If its a super fancy window air, that second thermostat could control a warming device to prevent the icing.
It sounds like you have an option figured out. If you get curious, search the model# on the net and you may come up with a schematic. Sometimes a super cheap option is to replace the temperature setting thermostat with a refrigerator or freezer thermostat of the same voltage. Tricks it into thinking it is a refrigerator.

12

The coils shouldn’t ice up if you can keep the humidity low in the cool room.