Charge Assist; Power Interrupt Delay; Heat Pump Cooling Mode Of Operation - Trane ACONT900AC43UA Service Manual

Sequence Of Operation
Refer to the schematic diagram on page 7

Charge Assist™

See the Service Facts in the outdoor unit for detailed information
on the Charge Assist™ feature.
MODE button: To enter the Charge Assist™ feature, press the
MODE button for 2 seconds.
6) CHARGING LED: When using the Charge Assist™ feature to
commission a system or check the charge level, this LED will
flash to indicate the start of the stabilization mode. The LED
flash rate will get faster the closer the system is to determining
the charge level.
7) ADD LED: When using the Charge Assist™ feature to
commission a new system or check the charge, the ADD LED
will turn ON if the operation calculates that the system
subcooling level is low. Should this LED turn ON, 24 volts AC
will be provided from terminals T3 and T4 of the Charge Assist™
control board to power a charging solenoid, if used. Note: See
the instructions supplied with the BAYCAKT001A (Literature
number 18-HH15D1-1). When the charging solenoid receives
power, the valve will open allowing refrigerant to flow from a
supply bottle to the outdoor unit via the Charging Port located
near the service valves. Once enough refrigerant has been
added to meet the subcooling requirement for the system and
the calculated charge level has been achieved, the control will
stop sending 24 volts AC from T3 &T4 de-energizing the charging
solenoid ending the flow of refrigerant to the system. At this
time the ADD LED will turn OFF and the CHARGED LED will turn
ON.
8) CHARGED LED: Utilized as an indicator during Charge Assist™
to acknowledge when the system charge is deemed to be "on
target" for the calculated subcooling level. DIP Switch settings
are required to be set before using the Charge Assist™ feature
in order to modify the subcooling level based on line length and
lift.
9) REC LED: This LED (Recover) will turn ON if the operation
calculates that the system subcooling level is high. Should the
REC LED turn ON, the system will be turned OFF for up to one
hour with the REC LED illuminated. The one hour lockout can be
exited by pressing the MODE button for two seconds or by
cycling power to the outdoor unit.
10) LOW Pressure LED: System pressure must be at least 90
psi (R-410A) to enter Charge Assist™. If system pressure is
sensed to be low, based on input from the Liquid Pressure
Transducer, this LED will turn ON for 30 seconds followed by
10 fast flashes from the CHARGING LED. These actions indicate
that Charge Assist™ was not allowed.
HP - A 8
20 SEER Sequence of Operation
11) ODT Out Of Range LED: Outside temperature must be at
least 55 degrees F to enter Charge Assist™. If the outside
temperature is sensed to be low, based on input from the Ambient
Temperature Sensor, this LED will flash for 30 seconds followed
by 10 fast flashes from the CHARGING LED.
12) DS13 LED: Functions only to transmit LitePort data which
requires an optic coupler and accompanying software to monitor
or record outdoor unit performance.
Note: Charge Assist TM always forces high stage operation.

Power Interrupt Delay

Power Interrupt protection is part of the control logic to prevent
short cycling of the compressor due to brief power interruptions
(0.1 to 1 second in duration). 24 volt AC power is required as an
input to the control at pin 11
the Power Interrupt logic to work. If 24 volt AC power is missing
on pin 11 of the J1 connector, the control board will send an
Error 18 message to the comfort control
the FAULT LED 18 times. If this fault is present, all system
operations will be allowed however; the fault indication will
persist until the 24 volt input to J1-11
Interrupt protection, if activated, will de- energize 24 volts AC to
the contactor and hold off compressor operation for
approximately 70 seconds. The STATUS LED plus the Y1 and/or
Y2 LEDs will flash for the duration of the Power Interrupt delay.
If a power-off cycle lasts 2 seconds or longer, the Minimum
Equipment Off Timer (5 minutes) will be enforced by the Comfort
Control.

Heat Pump Cooling Mode of Operation

When a heat pump system receives a demand message for
cooling capacity, in addition to the compressor contactor and
outdoor fan control signals, there is also a 24 volt AC output
from plug J3/3 (O) to energize the switchover valve (SOV)
13
solenoid coil. The SOV solenoid coil
14
with the start of the first call for cooling and remains energized
until the next call for compressor heat so long as the comfort
1
control stays in the cooling mode of operation.
of the J1 connector in order for
12
and begin to flash
1
is restored. Power
12
14 will be energized