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4–10

4.9.5

High Ambient Defrost Operation

High ambient defrost is used if the ambient air tem-
perature is greater than 80°F (26.7°C). The High Ambi-
ent Defrost Cycle has three separate actions:
a. Pump Down - The system pumps the low side of the
refrigeration system down to a lower suction pressure,
and reduces the engine load normally seen at the
beginning of a Defrost Cycle. The controls will be as
follows:

The unit will remain in pump down until the following
conditions are met:

• A minimum of 30 seconds, and the suction pres-

sure is less than 10 PSIG (0.68 bar)

• A maximum of 5 1/2 minutes, regardless of suc-

tion pressure.

b. High Ambient Defrost - Following pump down, the
defrost cycle will begin. The controls will be as follows:

NOTES

1. When in defrost, control of SV2 is the same as

in Heat Mode. Refer to

Section 4.4.3

2. When the Ambient Air Temperature is greater

than 35°F (1.7°C) at the beginning of the defrost
cycle

and

the discharge pressure rises to 340

psig (23.1 bar), UL1 will unload for the remain-
der of the cycle.

3. If discharge pressure rises to 350 psig (23.8

bar), the SV1 valve will open for 1 second and
continue to cycle as often as every 30 seconds
to reduce the pressure to less than 350 psig
(23.8 bar).

4.9.6

High Ambient Defrost Termination
Sequence

The following sequence will be used for high ambient
defrost termination:

• The unit will remain in High Speed and the

CSMV will reset to the position it was in at the
start of defrost.

• The control system will open SV1, open SV2

and unload UL1.

• When suction pressure has risen 10 PSIG (0.7

bar) above start point or after 15 seconds, the
control system will place the unit in low speed,
close SV4 and unload UL2.

• After 5 seconds, the clutch will be engaged.
• After an additional 5 seconds, the control system

will return to normal temperature control and the
data recorder will record a Defrost Termination
Event.

4.10 USER SELECTED OVERRIDE OPERATION

Four optional software override programs are available
to the user. These programs include: Temperature
Range Lock, ProductShield, FreshProtect and Air Flow.
Information on how the unit operates under these pro-
grams is provided in the following sub-paragraphs.

4.10.1

FreshProtect

Supply Air Control

FreshProtect operates when:

• The FRESHPROTECT Functional Parameter is

not OFF

and

• The setpoint is above 32°F (0°C)

and

• The TEMPERATURE CONTROL Functional

Parameter is set for Return Air

and

• The unit is in Continuous Operation with the

return air temperature less than 10°F (5.6°C)
above setpoint or the unit is in Start–Stop Oper-
ation, return air temperature is within 5°F (2.8°C)
of setpoint and criteria for shutdown other than
compartment temperature has not been met.

The FRESHPROTECT Functional Parameter may be
set to:

FreshProtect places a flexible limit on how far below
setpoint the supply air temperature can drop while the
unit is running under the above listed conditions.

4.10.2

Temperature Range Lock 1 & 2

Range Lock is a group of Configurations which may be
set to lock the unit into Start-Stop or Continuous Oper-
ation for various setpoint ranges.
Two ranges are available for selection. Each Range
can be independently set to lock it’s setpoint tempera-
tures into either Start-Stop or Continuous operation.
Each Range has it’s own selectable minimum and
maximum temperature, which define the span of the
range. If some setpoint temperatures are contained in
both ranges due to range overlap, Range 1 will always
have priority over Range 2.

SV1

SV2

SV4

Engine

Speed

Open

Low

Clutch

Output

UL1 & UL2

CSMV

Engage