# US 5,345,775 A · Refrigeration system detection assembly > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 5,345,775 A - Document ID: US5345775A - Status: Granted - Kind: A - Application number: 08/025,584 - Filed: 1993-03-03 - Granted: 1994-09-13 - Earliest claimed: 1993-03-03 - Inventors: Ralph G. Ridenour - Web page: https://patentgrep.com/patent/US5345775A ## CPC - F25D 21/006: {with electronic control circuits} - F25D 21/02: Detecting the presence of frost or condensate - F25D: REFRIGERATORS; COLD ROOMS; ICE-BOXES; COOLING OR FREEZING APPARATUS NOT OTHERWISE PROVIDED FOR (refrigerated showcases A47F3/04; thermally-insulated vessels for domestic use A47J41/00; refrigerated vehicles, see the appropriate subclasses of classes B60 - B64; containers with thermal insulation in general B65D81/38; heat-transfer, heat-exchange or heat-storage materials, e.g. refrigerants, or materials for the production of heat or cold by chemical reactions other than by combustion C09K5/00; thermally-insulated vessels for liquefied or solidified gases F17C; air-conditioning or air-humidification F24F; refrigeration machines, plants, or systems F25B; cooling of instruments or comparable apparatus without refrigeration G12B) ## Abstract A detection assembly is for a refrigeration system which has a cooling unit subject to frost build-up and defrost-to-drain. The assembly includes a first thermal sensor normally exposed to air but also to frost on the cooling unit or water in a plugged drain. A frost or water detection circuit has an input from the first thermal sensor, the detection circuit detects build-up of frost around the first thermal sensor and generates a defrost initiate DI signal which is connected to terminate the refrigeration to the cooling unit and then to initiate a defrost cycle wherein heat is applied to defrost the cooling unit. A second thermal sensor is in good thermal contact with said cooling unit, and a defrost terminate circuit has an input from said second thermal sensor to terminate the defrost cycle. A similar detection circuit determines the existence of ice or water in a plugged drain and terminates the refrigeration or indicates an alarm, or both. The foregoing Abstract is merely a resume of general applications, it is not a complete discussion of all principles of operation or applications, and is not to be construed as a limitation on the scope of the claimed subject matter. ## Claims ### Claim 1 A detection assembly for frost or water in a refrigeration system having a cooling unit subject to frost build-up and defrost water to a drain, said assembly comprising, in combination: a first thermal sensor normally exposed to air and mounted in said refrigeration system at a location subject to build-up of frost or water; a detection circuit having an input from said first thermal sensor; means in said detection circuit to energize said first thermal sensor with a voltage sufficiently high to cause said first thermal sensor to self-heat; and means to compare the resistance of said first thermal sensor at two different times to detect the presence of frost or water around said first thermal sensor and to generate a first signal; said first signal connected to terminate the refrigeration to said cooling unit. ### Claim 2 (depends on 1) A detection assembly as set forth in claim 1, wherein said two different times are during the self-heating of said first thermal sensor. ### Claim 3 (depends on 2) A detection assembly as set forth in claim 2, wherein said comparator means generates said first signal when there is sufficient frost or water build-up to prevent an appreciable temperature and resistance change on said first thermal sensor at said two different times. ### Claim 4 (depends on 1) A detection assembly as set forth in claim 1, wherein at least one of said two times is during the self-heating of said first thermal sensor. ### Claim 5 (depends on 1) A detection assembly as set forth in claim 1, wherein one of said two times is after the self-heating of said first thermal sensor for a few seconds. ### Claim 6 (depends on 1) A detection assembly as set forth in claim 1, wherein one of said two times is near the beginning of self-heating of said first thermal sensor. ### Claim 7 (depends on 1) A detection assembly as set forth in claim 1, wherein one of said two times is near the end of self-heating of said first thermal sensor. ### Claim 8 (depends on 1) A detection assembly as set forth in claim 1, wherein said thermal sensor is a thermistor. ### Claim 9 A detection assembly as set forth in claim in wherein said thermal sensor is a temperature dependent resistor. ### Claim 10 (depends on 1) A detection assembly as set forth in claim 1, including in said detection circuit a means to periodically heat said first thermal sensor to generate said first signal only if frost or water is present at said first thermal sensor. ### Claim 11 A plugged drain detection assembly for a refrigeration system having a cooling unit subject to frost build-up and a defrost-to-drain, said assembly comprising, in combination: a thermal sensor exposed to air and mounted in the refrigeration system drain; a plugged drain detection circuit having an input from said thermal sensor; means in said detection circuit to energize said thermal sensor with a voltage to cause said thermal sensor to self-heat; and means to compare the resistance of said thermal sensor at two different times to detect the presence of frost or water around said thermal sensor and to generate a plugged drain signal. ### Claim 12 (depends on 11) A plugged drain detection system as set forth in claim 11, wherein said thermal sensor is mounted in a defrost water drain of the refrigeration system. ### Claim 13 A defrost-on-demand assembly for a refrigeration system having a cooling unit subject to frost build-up, said assembly comprising, in combination: a first thermal sensor exposed to air and mounted a small distance from a cooling unit subject to frost build-up; a frost detection circuit having an input from said first thermal sensor; means in said detection circuit to energize said thermal sensor with a voltage to cause said thermal sensor to self-heat; and means to compare the resistance of said thermal sensor at two different times to detect the presence of frost around said thermal sensor and to generate a defrost initiate DI signal; and said DI signal connected to terminate the refrigeration to said cooling unit. ### Claim 14 (depends on 13) A defrost-on-demand assembly as set forth in claim 13, including said DI signal connected to initiate a defrost cycle wherein heat is applied to defrost said cooling unit; a second thermal sensor mounted to be in good thermal contact with said cooling unit; and a defrost terminate circuit having an input from said second thermal sensor to terminate said defrost cycle. ### Claim 15 (depends on 13) A defrost-on-demand assembly as set forth in claim 13, including a mounting block having a mounting surface; means to mount said mounting surface of said block on the cooling unit; and said first thermal sensor mounted in said mounting block. ### Claim 16 (depends on 15) A defrost-on-demand assembly as set forth in claim 15, including said second thermal sensor mounted in said mounting block to be in good thermal contact with said cooling unit. ### Claim 17 (depends on 14) A defrost-on-demand assembly as set forth in claim 14, including in said defrost terminate circuit a means to terminate the defrost cycle only when the temperature of said second thermal sensor is above 32.degree. F. ### Claim 18 (depends on 14) A defrost-on-demand assembly as set forth in claim 14, including means in said terminate defrost circuit to determine when the temperature of said second thermal sensor rises to about 35.degree. F., and to generate a defrost terminate signal RO to restart the refrigeration to the cooling unit.