Refrigeration system defrost initiation apparatus

Claim 1

A defrost initiation apparatus in combination with a refrigeration system having an evaporator coil to be occasionally defrosted, the refrigerator system having a fluid in motion passing in heat exchange relation to be cooled by said coil during its operation, a bypass passage around said coil for a portion of said fluid, an impeller enclosed within said bypass passage and adapted to be revolved by the motion of said fluid passing therethrough, and switch means connected to said impeller to be actuated in response to a condition of revolution of said impeller, said switch means including a clock timer gear train driven by said impeller, whereby said switch means is adapted to count the number of revolutions of said impeller and is actuated to thereby initiate a defrost cycle for said system after a predetermined number of said revolutions.