Heat pump system defrost control

Claim 1

An outdoor coil defrost control system (hereinafter "defrost control system") for a reverse cycle refrigeration system (hereinafter "system") for heating and cooling a building wherein said system comprises refrigerant compression means, an indoor coil, an outdoor coil, and refrigerant conduit means connecting said compression means and said coils, said defrost control system comprising: first outdoor coil temperature sensing means (hereinafter "TODCSA") having an output indicative of outdoor air temperature (hereinafter "TODCA"); second outdoor coil temperature sensing means (hereinafter "TODCS") having an output indicative of the temperature of said outdoor coil (hereinafter "TODC"); means (hereinafter "COM") operatively associated with said compression means and adapted to have an output indicative of the operation of said compression means; and controller means having operative connections to said TODSCA, TODCS, and COM so as to receive the outputs thereof, said controller having a TODCA monitoring function which is initiated upon (i) TODC being at or below a preselected value and (ii) said compression means being operated, said controller means further comprising (1) a variable frequency electronic oscillator having an input connected to TODCSA by means so as to receive a signal indicative of TODCA and an output signal the frequency of which is maximum at a preselected value of TODCA and continuously decreases as the value of TODCA deviates either above or below said preselected value; (2) a counter means having an input connected to receive the output signal of said variable frequency oscillator; and (3) means for connecting said counter means to said system, and being adapted, upon said counter means counting a preselected number of pulses, to place said system into an outdoor coil defrost mode of operation.