Abstract: An adaptive defrost control for a refrigerator is shown in which a single linear power supply (12) and microprocessor (U1) is used for both the adaptive defrost and cold control functions. According to a feature of the invention, a zero current crossing point switching scheme may be used to improve relay cycle life. According to another feature, a calibration procedure based on line frequency may be used to obtain multiples of a selected unit of time for any accumulated compressor run time and defrost heater energization times. According to another feature a sample and hold technique may be used to distinguish between noise and valid signals.