Amana SR520T Service page 22

Electronic Functional Description
Adaptive Defrost Operation
Defrost occurs after predetermined length of
compressor run time. Compressor run time between
defrosts changes, or adapts, depending upon recent
history of defrost lengths (time it takes for defrost
terminator to open after defrost heater has been
turned on).
• Defrost terminator opens at 9°C (48°F) and closes
at -9°C (15°F).
• Compressor run time between defrosts (CRTD)
will be one of 3 values under normal operation:
CRTD 1 (6 hours) or CRTD 2 (9 hours) or CRTD 3
(12 hours).
If defrost length is low (DT-LO defined as 21
minutes) indicating small frost load, CRTD for
next defrost cycle is advanced to next level.
If defrost length is high (DI - HI defined as 24
minutes) indicating large frost load, CRTD for
next defrost cycle is lowered to next level.
If defrost length is between 21 and 24 minutes,
CRTD for next defrost cycle remains the same.
Initial value at power up CRTD 0 is 3 hours.
• Vacation Mode CRTD equals 72 hours. Vacation
Mode CRTD is interrupted with door openings.
Defrost interval will revert back to interval before
Vacation Mode. Three things must occur to reach
Vacation Mode CRTD:
1) Defrost interval must be CRTD 3 (12 hours).
2) Both refrigerator and freezer doors must have
remained closed since last defrost cycle.
3) Defrost thermostat must have opened in less
than 21 minutes during last defrost cycle.
• Six minute dwell time occurs after defrost
terminator opens before compressor and
condenser fan motor will operate. Ten minute
dwell time occurs after defrost terminator opens
before evaporator fan motor will operate. Dwell
time can be bypassed by disconnecting power to
the unit for 30 seconds.
• Conventional defrost can be selected in Program
Mode B.
RS5290000 Rev. 0 24 April 1998