Retrofittable air conditioner to refrigeration conversion unit
A conversion unit for an air conditioning system to cause it to act like the cooling unit of a refrigeration system comprises a frost detector, an A/C temperature control defeating mechanism and a control unit which operate together to force the range of operation of the air conditioning unit into the range of operation of a refrigeration unit. The conversion unit is particularly useful for providing low cost cooling systems for farmers in third world countries for keeping their produce fresh and safe, not to mention its use by all farmers around the world and by florists or others in need or desire of an economical refrigeration alternative. The present invention is also usable to provide inexpensive cooling to RV's and to refrigerated vehicles.
1. A method of keeping food, produce or crops at a reduced temperature by cooling a volume to a refrigeration temperature, the volume being defined at least in part by a wall, the method comprising:
(a) mounting an unmodified conventional room air conditioning unit of the type that has an air conditioner temperature sensor with a lower cutoff temperature of 60° F. or higher, a compressor, and cooling fins, through the wall of the volume with the cooling fins and the temperature sensor disposed inside the volume;
(b) mounting a frost sensor on the fins of the air conditioning unit;
(c) mounting a heater in close proximity to the temperature sensor of the air conditioning unit;
(d) locating a room temperature sensor in the volume in a location remote from the heater and the frost sensor; and
(e) operating a control unit having inputs coupled to the frost sensor and the room temperature sensor and an output coupled to the heater, to cause the air conditioner to reduce the temperature in the volume to a desired reduced temperature below the lower cutoff temperature of the air conditioner temperature sensor while avoiding significant frost build up on the fins by the steps of:
(i) monitoring an ambient temperature in the volume with the room temperature sensor;
(ii) if the room temperature sensor indicates that the ambient temperature in the volume is above the desired reduced temperature, activating the heater to apply heat to the temperature sensor of the air conditioning unit such that the temperature sensor of the air conditioning unit senses a temperature above the designed lower cutoff temperature of the air conditioning unit and the air conditioning unit turns on the compressor;
(iii) when the room temperature sensor indicates that the ambient temperature in the volume is at or below the desired reduced temperature, deactivating the heater, such that the air conditioning unit turns off the compressor; and
(iv) enabling the heater in response to a negative reading of the frost sensor and disabling the heater in response to a positive reading of the frost sensor so as to ameliorate the buildup of frost on the fins.
2. The method of claim 1 , further comprising the step of the control unit delaying the activating of the heater in step (e)(ii) for a selected delay period after the room sensor senses a temperature above the desired reduced temperature and the frost sensor does not detect a frost condition.
3. The method of claim 1 , in which the desired reduced temperature is near freezing.