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Hello, yours is a real challenging question. I myself have gotten air conditioning equipment designed to run no cooler than 70F to run down to 50F.
The system must be greatly oversized to the normal load (cooling capacity per square foot)... and have defrost provisions added or the cooling coil will run so cold that it accumulates ice.
No normally sized unit designed for air conditioning will run much below 70F without icing... portable units in particular.
(Portable units exhaust air from the room, and that causes the air pressure inside the room so that to offset that exhaust, warm outside air must be drawn in.)
I am a retired mechanical engineer, HVAC specialist, and can help you come up with a solution if you can tell me why you need 50F, and what your humidity requirements at that temperature, and the size of the room.
I can even offer to completely design a workable system for you on our premium service terms.
i actually saw this in operation in a small closet sized room, down to 43 degrees with no icing using an LG portable inside the closet, venting into a larger room. He purchased a thermostat on amazon or ebay, but I just cannot remember the name. He is a snake breeder and uses it to brumate snakes, and it has been very dependable for him for years. I know this to be absolutely true. No humidity control either. The temperature in the exhaust room, which is maybe 12x15x8h, is a constant 83 degrees. If I could just remember the name of that thermostat my problem would be solved, but I just cant.
Hello, yes, in a closet sized room you can get many standard sized AC units to cool to 43F, but the thermostats need to be replaced... in such an application the portable unit, generally good for 300 square feet per 12,000 btu rating will easily cool a 30 sq ft closet to 43F. The unit will cycle on and off frequently enough so that any frost melts from the coil in the off cycle.
That is a ten to one oversized ac unit ratio in relation to the size of the closet.
Regarding the thermostat, if his entire AC unit shuts off when 43F is reached, fan stops as well, then I can specify a thermostat that will work easily for you.
Let me know about that, we can go from there.
What is that thermostat? That was the point of this entire thread.
The thermostat selected depends *entirely on the fan going off or the fan staying on once the closet reaches 43F... that is crucial.
If the fan goes off on your friends unit when its not blowing cold air, then a line voltage thermostat wired in series with line 1 on the power cord will be easy to locate and install. Chances of that are in the 98% range
IF however the fan stays on, (very unlikely as that would exhaust the cold air in the closet) then things get very much more complex (2% chance your friends system is wired that way)
We can go from here without a time limit.