Defrost; Defrost Initiation And Start; Defrost Modes - Carrier VECTOR 6500 Operation & Service Manual

4.6 DEFROST

Defrost is an independent cycle overriding cooling and
heating functions in order to de-ice the evaporator. When
the unit is in defrost, the DEFROST LED will be on, the
MessageCenter will display
STARTED for 5 seconds. The center of the Main Display
will show "dF". However, defrost will not be allowed when
the 1DDT is above 40.0_F (4.4_C).

4.6.1 Defrost Initiation And Start

Defrost can be initiated by pressing the MANUAL
DEFROST key or automatically by the microprocessor.
Microprocessor initiation is based on coil condition or
expiration of the defrost timer.
a. Defrost based on coil condition
Defrost based on coil condition will be initiated when:
• blockage is sufficient to cause an air pressure differ-
ential across the coil great enough to close the con-
tacts of the defrost air switch (DAS).
• when the RAT - 1DTT temperature is greater than
36°F (20°C) for 15 continuous minutes. This method
of defrost initiation will only be used for 3 consecutive
defrosts. After three consecutive defrost initiations by
this method the counter will be reset to allow this de-
frost initiation again only after a defrost cycle is initi-
ated by another method (timer, air switch or manual).
Ice is not the only thing that will cause the air dif-
ferential to increase across the evaporator coil.
Shrink wrap, paper, plastic bags, and other
such items when caught in the return air stream
and pulled up against the evaporator coil or the
return air grille can also cause the DAS contacts
to close.
b. Defrost based on time:
Time interval between defrosts is selected in the
microprocessor Functional Parameters. The parameter
value may be set to 1.5, 3, 6, or 12 hours. The factory
default setting is 6 hours.
NOTE
The defrost timer will not count when the unit is
in defrost, the unit is in a Start/Stop off cycle or
the 1DTT is greater than 40.0_F (4.4_C).

4.6.2 Defrost Modes

There are two defrost modes available, Normal Defrost
and Natural Defrost:
NOTE
When the unit is in defrost and in Engine opera-
tion:
the condenser fan will operate to supply air
S
for the radiator.
S the engine will operate in high speed when
the heaters are energized (to supply power
for the heaters).
62-11389
DEFROST CYCLE
OR
TIP
S the engine will operate in low speed when
the heaters are de-energized.
a. Normal Defrost Mode
Normal Defrost Mode will be entered if RAT is less than
39.2_F (4.0_C) and SAT is less than 45.0_F (7.2_C).
Defrost will be accomplished by shutting down the
refrigeration system (which includes the evaporator fan)
while the heaters are energized.
b. Natural Defrost Mode
Natural Defrost Mode uses a combination of the heat
from the product and the electric heaters to melt any ice.
Natural defrost is available when:
S the Natural
Configuration is set to YES and
S defrost is initiated by closing of the DAS
contacts with RAT greater than or equal to
39.2_F (4.0_C) and
S at least one normal defrost has been
performed since power up.
When a natural defrost is initiated, the unit will operate
for the first five minutes with the evaporator fan and
HTCON2 de-energized and only HTCON1 energized.
After 5 minutes the evaporator fan is energized while
both HTCON1 & HTCON2 are de-energized.
Only 3 consecutive natural defrosts cycles are allowed.
After there have been 3 consecutive natural defrost
cycles, the next defrost will be a normal deforst.
4.6.3 Defrost Termination
When in normal defrost mode, defrost will terminate
when the 1DTT rises to 55_F (12.8_C).
When operating in natural defrost, defrost will continue
for a minimum of 5 minutes, a maximum of 10 minutes,
or until the SAT is equal to or higher than the RAT.
When the unit exits defrost, the engine will go to low
speed. "dF" will continue to be displayed in place of
compartment temperature, and the COOL LED will
come on when the compressor starts.
The EVXV will open, and the evaporator coil will begin to
cool down. The evaporator fan will not come on right
away, so that warm air is not blown into the refrigerated
compartment, but will wait for the evaporator to cool
down, up to a maximum of 8 minutes. Once the
evaporator fan has started, "dF" will no longer be
displayed, and refrigerated compartment temperature
will again be shown in the main display.
If a 1DTT sensor alarm has been activated, defrost will
terminate after 10 minutes.
Defrost uses a Defrost Duration Timer that al-
lows for a maximum of 45 minutes in defrost. If
defrost is not terminated during the 45 minutes,
the microprocessor will end the defrost cycle,
and activate the A54 - "DEFROST NOT COM-
PLETE" alarm. When this occurs, the Defrost
Interval Timer is set for 1.5 hours, at which time
the unit will go into defrost again.
4−8
Defrost microprocessor
NOTE