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© 2016 Emerson Climate Technologies, Inc.
AE5-1412 R1
6.17. Crankcase Heater
The crankcase heater is energized when the ambient
temperature is below 50°F and the compressor is off.
If an ambient sensor fails, the crankcase heater is
energized when the compressor is off.
6.18. Suction Pressure Control
The compressor is operated based on the suction
pressure cut-in (
Cin
) and cut-out (
CoU
). If the suction
pressure rises above the cut-in, the compressor is
turned on using the startup procedure (See Section
6.14). If the suction pressure then falls below the cut-
out, it turns the compressor off using the shutdown
procedure (See section 6.16).
The compressor remains off for a minimum 120
seconds (
2oF
) after shutdown, which is adjustable in
the advanced options menu (See section 6.3).
If the suction pressure transducer fails, the compressor
will run in limp along mode. The compressor will stay
off for 3 minutes (
CoF
) then run for 3 minutes (
Con
).
These values are adjustable from the advanced options
menu (See section 6.3).
The cut-in and cut-out settings are adjustable between
0 PSIG and 135 PSIG.
IMPORTANT: At initial power up, depending on the
suction pressure transducer, the suction pressure
could be higher than the rating of the transducer. For
15 minutes after power up, any over pressure errors
generated by the suction pressure transducer should be
ignored, and the display will flash 135. If the transducer
is still in an error state after the time has expired, the
control will alarm that the suction pressure transducer
signal is lost, and go into limp along mode.
6.19. Fan Control
The The X-line uses variable speed PSC condenser
fan motors to maintain the head pressure values that
allow the system to operate within the compressor
operating envelope and maintain the minimum pressure
differential across the expansion device to allow it to
operate properly.
The controller uses a Proportional-Integral (PI) control
algorithm to determine the fan speed. The fans will
not run any slower than 40% before turning off. When
a fan first turns on it will run for 3 seconds at full speed
before it begins modulating. Fans will run for at least
10 seconds before turning off and stay off for at least
10 seconds before being turned back on.
Since the X-Line controller knows the current suction
pressure, the controller can determine the minimum
condensing point for the condition the unit is actually
running, and will adjust the fan control set point to
maintain that temperature or higher.
The XFAP/XFAM and XFAL models have different
compressors and different refrigerant options.
Therefore, during commissioning, it is important to
identify the seleted refrigerant so the controller will
operate the fans properly.
Low ambient operation
The condensing unit can operate in outdoor ambient
temperatures as low as -40°F. The unit will automatically
adjust condenser fan speed to maintain head pressure.
At extremely low ambient temperature the condenser
fan might not run, but the condenser coil is still
discharging heat. Parameter LAS sets the ambient
temperature required to initiate low ambient on time.
The default value is -20°F. Parameter LMO sets the
low ambient minimum on time. The default value is 6
seconds. Below -20°F ambient, when the condensing
unit runs it will run for a minimum of 6 seconds.
IMPORTANT NOTE:
To fully utilize low condensing
options below 70°F condensing, an electronic
expansion valve (EXV) is normally required to handle
the larger variation in mass flows. As a result, the unit
is shipped with a default minimum condensing override
value of 70°F (80°F for XFAL). The fans will still follow
the map of the selected refrigerant, but the map will
not be allowed to run below the override value. If you
have a system with an EXV installed, you can adjust
the value by changing parameter MCS in the advanced
options menu.
6.19.1. Fan Overrides and Error Handling
If the discharge line temperature is above 205°F the
fans will run at full speed.
If the condenser mid-coil temperature sensor fails, the
fan speed is determined by outdoor ambient. If both
the outdoor ambient sensor and the condenser mid-coil
temperature sensor fail, all fans will run at full speed.
