General Information; Low Ambient Cooling; Defrost/Defrost Hold; Stage Control Board - Carrier 25HNA6 Installation Instruction

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A06525
Fig. 6 - 2-Stage Control Board
GENERAL INFORMATION
Low Ambient Cooling
When this unit is operating below 55°F (12.78°C) 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 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 (4.4°C) OAT. Fan will
cycle based on coil and outdoor air temperature.
Infinity controlled low ambient mode operates as follows:
• Fan is OFF when outdoor coil temp is < (outdoor air temperature
+ 3 oF/1.7 oC) or outdoor fan has been ON for 30 nfinutes. (Fan is
turned off to allow refrigerant system to stabilize.)
• Fan is ON when outdoor coil temp > (outdoor air temperature +
25 oF/13.9 oC) or outdoor coil temp > 80 ° F/26.7 oC or if outdoor
fan has been OFF for 30 minutes. (Fan is turned on to allow
refrigerant system to stabilize.)
• Low pressure switch is ignored for first 3 nfinutes 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 nfinutes 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 nfinutes, then the normal LPS trip response (shut down
cooling operation and generate LPS trip error) will occur.
For 25HNA9 models, the PWM output for both high and low stage
equals the value for low stage operation below 104°F (40°C).
Defrost
This control offers 5 possible defrost interval times: 30, 60, 90, 120
nfinutes, or AUTO.
On 25HNA6 models, these are selected by dip switches on the unit
control board or by the Infinity Control User Interface. The
A06526
Infinity Control selection overrides the control board dip switch
settings.
On 25HNA9 , the defrost interval times: 30, 60, 90, and 120
nfinutes or AUTO are selected by the Infinity Control User
Interface (the dip switches are not used.)
AUTO defrost adjusts the defrost interval time based on the last
defrost time as follows:
• When defrost time <3 nfinutes, the next defrost interval=120
minutes.
• When defrost time 3-5 nfinutes, the next defrost interval=90
minutes.
• When defrost time 5-7 nfinutes, the next defrost interval=60
minutes.
• When defrost time >7 nfinutes, the next defrost interval=30
nfinutes.
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 32°F (0°C) for 4 nfinutes
during the interval.
The defrost cycle is ternfinated when the coil temperature reaches
65°F (18.33°C)or 10 nfinutes has passed.
If the coil temperature does not reach 32°F (0°C) within the
interval, the interval timer will be reset and start over.
• Upon initial power up the first defrost interval is defaulted to 30
nfinutes. Remaining intervals are at selected times.
• Defrost is only allowed to occur below 50°F (10°C)outdoor
ambient temperature.
Defrost Hold
On 25HNA6 models, in a non-conmmnicating system, if the
thermostat becomes satisfied (YI or YI and Y2) before the defrost
cycle is ternfinated, the control will "hold" in defrost mode and
finish the defrost cycle on the next call for heat.
On 25HNA6 models, with conmmnicating Infinity Control and all
25HNA9 models, defrost hold is not needed in a conmmnicating
system because the User Interface will complete the defrost cycle
before shutting down the system.