Operating instructions

TM 11574A-OI
2-56
(4) Sequence Of Operation – Defrost
The defrost cycle may consist of up to three distinct operations. The first is de-icing of the
coil, the second is a probe check cycle, and the third is snap freeze. Defrost may be
requested by any one of the following methods:
The manual defrost function (also manual defrost switch function if equipped) is initiated and
ended by the user using the keypad or manual defrost switch (if equipped).
NOTE
The Manual Defrost/Interval key can be used to initiate a manual defrost. Minimum Software
release version #5126 is required in order to use this function.
Manual Defrost/Interval Key Operation:
(a) Depressing and holding the Defrost Interval key for five seconds will initiate defrost. If the
defrost interval key is released in less than five seconds, defrost interval (code 27) shall
be displayed.
(b) The defrost interval timer (controller function code Cd27) reaches the defrost interval set
by the user.
(c) The controller probe diagnostic logic determines that a probe check is necessary based
on the temperature values currently reported by the supply and return probes.
(d) The controller Demand Defrost configuration variable (CnF40) is set to “In” and the unit
has been in pull down operation for over 2.5 hours without reaching set point.
Figure 2-22. Defrost.