Circuit Board; Crankcase Heater Operation; Outdoor Fan Motor Operation; Time Delays - Carrier Infinity 25VNA0 Service Manual

Circuit Board

The variable speed circuit board is a serially communicating device
that receives capacity demands from the Infinity wall control and
communicates corresponding speed request to the Inverter Drive,
which controls compressor to the speed demanded.
The variable speed HP circuit board also controls the EXV to either
provide superheat or act as a load- -shedding tool.
The circuit board 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 (25VNA0)
— Intelligent Defrost (25VNA0)
— Low Ambient Cooling
— Hold at compressor speed on start- -up
— Wall control holds demand to minimum for 5 minutes
Motor Control Drive (Inverter):
S Converts the sinusoidal AC input mains voltage into a
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.
S The drive control algorithms insure the magnetic field set
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:
Through the combination of the drive and motor, the
S
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. 2) 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 wall control.
S Five minute compressor re- -cycle delay on return from a
brown- -out condition.

Infinity Controlled Low Ambient Cooling

This unit is capable of low ambient cooling down to 0F (- -17.8C)
with Low Ambient enabled on the
ambient kit is not required. The only accessory that may be
required is wind baffles in locations which are likely to experience
cross winds in excess of 5 miles an hour. This generally occurs
only on roof and open area applications. The Infinity Control
provides an automatic evaporator freeze thermostat. Low ambient
cooling must be enabled in the wall control setup. 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:
S Fan is OFF when outdoor coil temperature is too low (+
55_F/12.7_C), the saturated suction pressure indicates a freezing
indoor coil or outdoor fan has been ON for 30 minutes. (Fan is
turned off to allow refrigerant system to stabilize.)
S Fan is ON when outdoor coil temperature is too high
(+80_F/26.7_C), the high side pressure is too high or if outdoor
fan has been OFF for 30 minutes. (Fan is turned on to allow
refrigerant system to stabilize)
S Low pressure indication by the suction pressure transducer is
ignored for first 3 minutes during low ambient start up. After 3
minutes, if low pressure trip occurs, then outdoor fan motor is
turned off for 10 minutes, with the compressor running. If
pressure condition is satisfied 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 suction pressure condition is not satisfied within 10 minutes,
then the normal trip response (shut down cooling operation and
generate LP trip error) will occur.

Utility Interface With Infinity Control

The utility curtailment relay should be wired between the two
UTIL connections on the control board for this Infinity
Communicating System. This input allows a power utility device
to interrupt compressor operation during peak load periods. When
the utility sends a signal to shut the system down, the wall control
will display, "Curtailment Active". See wall control installation
instructions for setup details.
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Infinity Control. A low