Electronic Expansion Valve (Exv); Controller; Crankcase Heater; Outdoor Fan Motor - Carrier 25VNA Service Manual

Electronic Expansion Valve
Fig. 2 – Electronic Expansion Valve (EXV)
An EXV is used for accurate refrigerant metering in the heating
mode. It enables the system to achieve high HSPF rating.
The outdoor board senses suction pressure and temperature to
control EXV movement.
The EXV has a stepper motor with 600 steps from fully open to
fully closed
Cooling
Valve is wide open
Heating
At start of each cycle, valve controls to a fixed position depending
on speed and ambient temperature for 120 seconds. This allows
the refrigerant system to stabilize. After this "pre- -set" period,
control board controls valve as needed to control suction superheat
and/or compressor load.
Defrost
Valve is wide open

Controller

The variable speed Heat Pump (VS HP) controller is a serially
communicating device that receives capacity demands from the
Infinity User Interface and communicates corresponding speed
request to the Inverter Drive, which controls compressor to the
speed demanded.
The VS HP Control also controls the EXV to either provide
superheat or act as a load- -shedding tool.
The VS HP Control also proactively tries to prevent fault trip
events by using sensors and Inverter feedback. Sensors include a
suction pressure transducer (SPT), an outdoor suction thermistor
(OST), the outdoor air thermistor (OAT), outdoor coil thermistor
(OCT), high pressure switch (HPS) etc.
Features:
— Serially Communicating
— 2 or 3 Wire
— DX+, DX- -
— Ground (optional)
— Capacity Feedback
— Ambient Optimized Speed Ranges
— Proactive Fault Prevention
— Automatic Load Shedding
— Heating Superheat Control with EXV
— Intelligent Defrost
— Low Ambient Cooling
— Hold at compressor speed on start- -up
— User Interface holds demand to minimum for 5 minutes
Motor Control Drive (Inverter):
Converts the sinusoidal AC input mains voltage into a
S
variable frequency AC output generated used PWM
modulation of the output.
S Drive adjusts the output voltage to run the compressor at
the correct speed at any load point in the envelope.
S The drive actively controls the motor current to insure
the proper torque is provided for the given loading
condition.
The drive control algorithms insure the magnetic field set
S
up in the motor is synchronized with the rotor insuring
smooth efficiency operation.
S The drive actively controls the input current at heavy
loading conditions to insure the input power factor to the
drive is >0.95.
Compressor Brushless Permanent Magnet Motor (BPM):
S The motor inductance reacts to the drive current and a
sinusoidal current is induced through the motor
windings.
S The sinusoidal current sets a rotating magnetic field, at
the frequency set by the drive.
S The magnets enable the motor to synchronize to that
frequency, set by the drive.
S Supplies the mechanical power afforded to it by the drive
voltage, current and frequency.
Motor Control Drive + BPM together:
S Through the combination of the drive and motor, the
system is able to operate over a wide speed range.
S The drive provides protection of the system to various
abnormal conditions including limiting the compressor
envelope of operation to appropriate boundaries.
S Provides many pieces of system data as feedback to the
system controller.
S Allows operation at least than full performance in case of
system faults or issues.
Crankcase Heater Operation
This unit has an internal crankcase heater that will be energized
during the off cycle and is intelligently demanded by the system to
prevent the compressor from being the coldest part of the system
thus enhancing the reliability. The crankcase heater will function
as needed any time the outdoor unit is powered. The indoor unit
and UI do not need to be installed for the crankcase heater to
operate properly.
NOTE: Contactor may close intermittently without the unit
starting. This is done to determine whether the control needs to
energize the crankcase heater. Closing the contactor powers the
inverter and allows the system to check compressor temperature.
Outdoor Fan Motor Operation
The outdoor unit control (Fig. 3) energizes outdoor fan anytime
compressor is operating, except for defrost and as needed during
low- -ambient cooling operation. The outdoor fan remains
energized if a pressure switch opens or compressor scroll over
temperature should occur. This OD fan is an ECM motor which
operates at varying speeds depending on the ambient and the
demand.

Time Delays

The unit time delays include:
S Five minute time delay to start cooling or heating operation
when there is a call from the user interface. To bypass this
feature, momentarily short and release Forced Defrost pins.
S Five minute compressor re- -cycle delay on return from a
brown- -out condition.
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