13
Low Ambient Cooling
When this unit is operating below 55ºF outdoor temperature,
provisions must be made for low ambient operation.
Infinity Controlled low ambient cooling:
This unit is capable of low ambient cooling without a kit ONLY
when using the Infinity control. A low ambient kit is not
required, and the outdoor fan motor does not need to be replaced
for Infinity controlled low ambient operation.
The Infinity
Control provides an automatic evaporator coil freeze protection
algorithm that eliminates the need for an evaporator freeze
thermostat. Low ambient cooling must be enabled in the User
Interface set up. Fan may not begin to cycle until about 40
_
F
OAT. Fan will cycle based on coil and outdoor air temperature.
Infinity controlled low ambient mode operates as follows:
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Fan is OFF when outdoor coil temp is < (outdoor air
tempe 3
_
F) or outdoor fan has been ON for 30
minutes. (Fan is turned off to allow refrigerant system
to stabilize.)
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Fan is ON when outdoor coil temp > (outdoor air
tempe 25
_
F) or outdoor coil temp > 80
_
F or if
outdoor fan has been OFF for 30 minutes. (Fan is
turned on to allow refrigerant system to stabilize.)
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Low pressure switch is ignored for first 3 minutes
during low ambient start up. After 3 minutes, if LPS
trips, then outdoor fan motor is turned off for 10
minutes, with the compressor running. If LPS closes
within 10 minutes then cooling continues with the
outdoor fan cycling per the coil temperature routine
listed above for the remainder of the cooling cycle. If
the LPS does not close within 10 minutes, then the
normal LPS trip response (shut down cooling operation
and generate LPS trip error) will occur.
Standard Thermostat low ambient cooling mode:
A Low Ambient Pressure Switch kit, Evaporator Freeze
Thermostat and Winter Start Control must be installed for low
ambient operation in standard thermostat mode. The fan motor is
a ball--bearing type and does not need to be changed. A crankcase
heater must be installed. See Product Data for part numbers on
appropriate unit size and series units.
DEFROST
This control offers 4 possible defrost interval times: 30, 60, 90 or
120 minutes. These are selected by dip switches on the unit
control board, or in the Infinity control (if used). The Infinity
Control selection overrides the control board dip switch settings.
Auto defrost is available with Infinity communicating control
only and it must be enabled in the User Interface. Auto defrost
adjusts the defrost interval time based on the last defrost time as
follows:
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When defrost time is < 3 minutes, the next defrost
interval = 120 minutes
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When defrost time is 3--5 minutes, the next defrost
interval = 90 minutes
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When defrost time is 5--7 minutes, the next defrost
interval = 60 minutes
S
When defrost time is > 7 minutes, the next defrost
interval = 30 minutes
The control board accumulates compressor run time. As the
accumulated run time approaches the selected defrost interval
time, the control board monitors the coil temperature sensor for a
defrost demand. If a defrost demand exists, a defrost cycle will be
initiated at the end of the selected time interval. A defrost demand
exists when the coil temperature is at or below 32º F for 4
minutes during the interval.
The defrost cycle is terminated when the coil temperature reaches
65º or 10 minutes has passed.
If the coil temperature does not reach 32 deg. within the interval,
the interval timer will be reset and start over.
NOTE
:
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Upon initial power up the first defrost interval is
defaulted to 30 minutes. Remaining intervals are at
selected times.
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Defrost is only allowed to occur below 50ºF outdoor
ambient temperature.
Defrost Hold
In a non--communicating system, if the thermostat becomes
satisfied before the defrost cycle is terminated, the control will
”hold” in defrost mode and finish the defrost cycle on the next
call for heat. Defrost hold is not needed in a communicating
system because the User Interface will complete the defrost cycle
before shutting down the system.
Forced Defrost
Forced defrost can be initiated manually in a non--communicating
system, or by communicated command from a User Interface.
The board contains a 2--pin header labeled FORCED DEFROST
(See Figure 14). To initiate a forced defrost:
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Manually, short FORCED DEFROST pins for 5
seconds then release
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If coil temp is at defrost temp of 32º F, and outdoor air
temperature is below 50ºF, a full defrost sequence will
occur
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If the coil temp or outdoor air temperature do not meet
the above requirements, an abbreviated 30 second
defrost will occur
25H
PA
