Residential Air Conditioners and Heat Pumps Using R-22 and Puron® Refrigerant: Application Guideline and Service Manual
Manufacturer reserves the right to change, at any time, specifications and designs without notice and without obligations.
55
System Functions and Sequence of
Operation (286B/89B/180B/187B)
The outdoor unit control system has special functions. The following is
an overview of the two-stage control functions:
Cooling and Heating Operation
The 286B/187B/289B/180B model utilizes either a standard 2-stage
indoor thermostat or Evolution Communication User Interface. With a
call for first stage cooling, the outdoor fan, reversing valve, and low
stage compressor are energized. If low-stage cannot satisfy cooling
demand, high-stage cooling is energized by the second stage of indoor
thermostat or User Interface. After second stage is satisfied, the unit
returns to low-stage operation until first stage is satisfied or until second
stage is required again. When both first stage and second stage cooling
are satisfied, the compressor will shut off. The reversing valve will
remain energized until the control board power is removed or a call for
heating is initiated. With a call for heating, the outdoor fan and
compressor are energized. The compressor will operate in high or low
stage operation, as needed to meet the heating demand. When the
heating demand is satisfied, the compressor and fan will shut off. The
reversing valve is de-energized in the heating mode.
NOTE:
When two-stage unit is operating at low-stage, system vapor
(suction) pressure will be higher than a standard single-stage system or
high-stage operation.
NOTE:
Outdoor fan motor will continue to operate for one minute after
compressor shuts off, when outdoor ambient is greater than or equal to
100
°
F. This reduces pressure differential for easier starting on next
cycle.
NOTE:
If unit has not operated within the past 12 hours, or following a
unit power-up, upon the next thermostat high- or low-stage demand, unit
operates for a minimum of 5 minutes in high-stage.
On models with non-communicating (non-Evolution) systems, with first
stage of cooling, Y1 and O are powered on; and with second stage of
cooling, Y1, Y2, and O are on. For these systems, with first stage of
heating Y1 is on and for second stage of heating, Y1 and Y2 are on.
When the reversing valve is energized, O is powered on.
Communication and Status Function Lights For
Evolution Control only, Green communications
(COMM) Light
A green LED
(COMM light)
on the outdoor board indicates successful
communication with the other system products. The green LED will
remain OFF until communication is established. Once a valid command
is received, the green LED will turn ON continuously. If no
communication is received within 2 minutes, the LED will be turned
OFF until the next valid communication.
Amber Status Light
An amber colored
STATUS light
is used to display the operation mode
and fault codes as specified in the troubleshooting section. See
for codes and definitions.
NOTE:
Only one code will be displayed on the outdoor unit control
board (the most recent, with the highest priority).
Utility Interface With Evolution Control
The utility curtailment relay should be wired between R and Y2
connections on the control board for Evolution Communicating Systems
only (see
.) 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 User Interface will display,
“Curtailment Active”.
Compressor Operation
The basic scroll design has been modified with the addition of an
internal unloading mechanism that opens a bypass port in the first
compression pocket, effectively reducing the displacement of the scroll.
The opening and closing of the bypass port is controlled by an internal
electrically operated solenoid.
The modulated scroll uses a single step of unloading to go from full
capacity to approximately 67% capacity. A single speed, high efficiency
motor continues to run while the scroll modulates between the two
capacity steps. Modulation is achieved by venting a portion of the gas in
the first suction pocket back to the low side of the compressor, thereby
reducing the effective displacement of the compressor. Full capacity is
achieved by blocking these ports, thus increasing the displacement to
100%. A DC solenoid in the compressor controlled by a rectified 24 volt
AC signal in the external solenoid plug moves the slider ring that covers
and uncovers these ports. The port covers are arranged in such a manner
that the compressor operates at approximately 67% capacity when the
solenoid is not energized and 100% capacity when the solenoid is
energized.
The loading and unloading of the two step scroll is done “on the fly”
without shutting off the motor between steps.
NOTE:
67% compressor capacity translates to approximately 75%
cooling or heating capacity at the indoor coil. The compressor will
always start unloaded and stay unloaded for five seconds even when the
thermostat is calling for high stage.
Fan Motor
Fan motor rotates the fan blade that either draws or blows air through
outdoor coil to exchange heat between refrigerant and air. Motors are
totally enclosed to increase reliability. This also eliminates need for rain
shield.
The bearings are permanently lubricated; therefore, no oil ports are
provided.
For suspected electrical failures, check for loose or faulty electrical
connections, or defective fan-motor capacitor. Fan motor is equipped
with thermal overload device in motor windings which may open under
adverse operating conditions. Allow time for motor to cool so device can
reset. Further checking of motor can be done with an ohmmeter. Set
scale on R X 1 position; check for continuity between three leads.
Replace motors that show an open circuit in any of the windings. Place 1
lead of ohmmeter on each motor lead. At same time, place other
ohmmeter lead on motor case (ground). Replace any motor that shows
resistance to ground, signs of arcing, burning, or overheating.
Located above the compressor is a single-speed fan motor and fan. The
180B/289B air conditioner and heat pump models use the ECM variable
speed fan motor.
The outdoor Integral Control Motor (ECM), is a variable-speed motor
which operates from 450 to 850 rpm. The motor is a dc permanent
magnet-type motor with the electronic controls integrated into its rear
cover. The control package includes a small diode bridge, capacitors,
and power switching devices. It converts ac to dc power and switches the
dc power to the motor windings on and off at various rates to control the
motor speed. The speed at which the motor windings are thus
commutated is determined by a pulse width modulated (PWM) signal
which is received from the control board on the motor control lines.
The PWM signal is created by turning a DC signal on and off once
within a given period of time. The signal on time relative to the signal
total period defines the percent of the PWM. For example, if the period
is 5 sec and the control power is turned on for 1 sec then off, the signal
will remain off for 4 sec before turning on again to start the next cycle.
WARNING
!
ELECTRICAL SHOCK HAZARD
Failure to follow this warning could result in personal injury or death.
Turn off all power to unit before servicing or replacing fan motor. Be
sure unit main power switch is turned off.
