Defrost control system

Claim 2

In a refrigerating system comprised of an electric motor driven compressor and an evaporator, a blower for circulating air over the evaporator, electrically controlled means operative to heat said evaporator to melt frost therefrom, switching mechanism operative to initiate and terminate operation of said evaporator heating means, an electric timer motor for actuating said switching mechanism to initiate and terminate heating of said evaporator, characterized by said timer motor comprising a hysteresis synchronous motor, circuit means to energize said timer motor including an AC power source, a diode and a gate controlled silicon rectifier in parallel circuit and series connected with said timer motor in said circuit means whereby said diode and rectifier are capable of conducting alternate waves respectively of the alternating wave voltage of said AC current, and means responsive to the collection of frost on said evaporator for applying a firing voltage to the gate of said silicon controlled rectifier for rendering said silicon rectifier conductive of substantially one-half wave of said AC current.

Claim 3

A refrigerating system as defined in claim 1 further characterized by means responsive to operation of said switching mechanism for applying a firing voltage to the gate of said silicon rectifier when said switching mechanism is operated to cause heating of said evaporator.

Claim 4

In a refrigerating system comprising an electric motor driven compressor and an evaporator, an air circulating structure for withdrawing air from a refrigerator compartment, forcing said air through the evaporator and returning to said compartment; means operative to heat said evaporator to melt frost therefrom; control means for said evaporator heating means including, a fluid amplifier device having a hollow body member, walls in said body member forming alternate air passages therethrough and control air passages intersecting at least one of the first mentioned air passages, means for connecting one end of said one air passage with the air stream of said circulating structure in an area immediately upstream of said evaporator and connecting the other end of said air passages with an area downstream of said evaporator in said air circulating structure, an electronic control circuit for said means to heat said evaporator and including a pair of resistors disposed in the respective alternate air passages; and means to supply electric current to said control circuit comprising a current supply circuit of high voltAge relative to the operating voltage of said control circuit and a voltage dropping resistor between said supply circuit and said control circuit, said dropping resistor being disposed in said hollow body and arranged to heat said walls comprising said control air passages.

Claim 5

In a refrigerating system comprising an electric motor driven compressor and an evaporator, an air circulating structure for withdrawing air from a refrigerator compartment, forcing said air through the evaporator and returning to said compartment; means operative to heat said evaporator to melt frost therefrom; control means for said evaporator heating means including, a fluid amplifier device having a hollow body member, walls in said body member forming alternate air passages therethrough and control air passages intersecting at least one of the first mentioned air passages, means for connecting one end of said one air passage with the air stream of said circulating structure in an area immediately upstream of said evaporator and connecting the other end of said air passages with an area downstream of said evaporator in said air circulating structure, an electronic control circuit for said means to heat said evaporator and including a pair of resistors disposed in the respective alternate air passages; and means to supply electric current to said control circuit comprising a current supply circuit of high voltAge relative to the operating voltage of said control circuit and a voltage dropping resistor between said supply circuit and said control circuit, said dropping resistor being disposed in said hollow body and arranged to heat said walls comprising said control air passages.

Claim 6

In a refrigerating system as set forth in claim 3 further characterized by said current supply circuit comprising an AC power circuit for said electric motor.