A defrost controller with timer (Figure 3.27) operates various control valves and fan relays to quickly and efficiently remove frost and ice accumulation from evaporator surfaces. There are four easy-to-set defrost steps:
• pump out,
• hot gas,
• equalize, and
• fan delay.
This controller uses reliable, solid-state electronics with a precision quartz time clock and time interval adjusting slide knobs to sequentially operate through the four steps for smooth defrosting. Each step is clearly indicated by a bright LED during operation. Terminals for optional sensor defrost initiation and termination are provided. A 24-hour quartz time clock facilitates simple setting in 15-minute increments of defrost start times. A 7-day quartz time clock for weekly scheduling is also available. All time clocks have 72-hour battery backup in case of short-term power failure. Because of its time-adjustable 4-step defrost operation, this controller is suitable for almost every defrost application including top and bottom feed unit coolers, blast freezer evaporators, ice makers, etc.