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11
MAJOR COMPONENTS
2--Stage Control Board
The HP control board controls the following functions:
S High and low stagecompressorcontactoroperation
S Outdoor fan motoroperation
S Reversing valveoperation
S Defro st operatio n
S Lo w amb ien t coo lin g
S Cran k case heater operation
S Compressorexternal protection
S Pressu re switch monitorin g
S Time Del ays
S On 286A models,high-- and low--stage start relay and
capacitoroperation (Bristol compressor only)
Field Connections
On models with non --communicating (non --Evolution) system, the
two--stage control receives 24vac low--voltage control system
inputs through the R, C, Y1, Y2 and O connections located at the
bottom of the control board (see Fig. 6.) On a non --communicating
system, output W1 is connected at the bottom of the control board
for auxiliary heat.
On models with communicating system, use the ABCD Evolution
connections.
Two Stage Compressor
The two stage compressor contains motor windings that provide
2-- pole (3500 RPM) operation. For two--stage compressor, refer to
Table 5 for correct winding resistance.
Compressor Internal Relief
The compressor is protected by an internal pressure relief (IPR)
which relieves discharge gas into the compressor shell when
differential between suction and discharge pressure exceeds
500-- 550 psi on 286A models and 550 --625 psi on 288A models.
The compressor is also protected by an internal overload attached
to motor windings.
Compressor Control Contactors
The contactor(s) have a 24volt coil. The electronic control board
controls the operation of the appropriate contactor.
TROUBLESHOOTING
Systems Communication Failure
If communication with the Evolution control is lost with the User
Interface, the control will flash the appropriate fault code. (See
Table 6.) Check the wiring to the UI and the indoor and outdoor
units.
Model Plug
Each control board contains a model plug. The correct model plug
must be installed for or the system to operate properly. (See Table
4.)
Table 4 – Model Plug Information
MODEL
NUMBER
MODEL PLUG
NUMBER
PIN RESISTANCE
(K --- ohms)
Pins 1 --- 4 Pins 2 --- 3
286A024 HK70EZ002 5.1 18
286A036 HK70EZ004 5.1 33
286A048 HK70EZ006 5.1 51
286A060 HK70EZ008 5.1 75
288A024 HK70EZ010 5.1 120
288A036 HK70EZ012 5.1 180
288A048 HK70EZ014 5.1 270
288A060 HK70EZ016 11 5.1
The model plug is used to identify the type and size of unit to the
control. On 286A models, the model plug is also used to determine
the start sequence timing for each individual model.
On new units, the model and serial numbers are input into the
board’s memory at the factory. If a model plug is lost or missing at
initial installation, the unit will operate according to the
information input at the factory and the appropriate error code will
flash temporarily. An RCD replacement board contains no model
and serial information. If the factory control board fails, the model
plug must be transferred from the original board to the replacement
board for the unit to operate.
NOTE: The model plug takes priority over factory model
information input at the factory. If the model plug is removed after
initial power up, the unit will operate according to the last valid
model plug installed, and flash the appropriate fault code
temporarily.
Pressure Switch Protection
The outdoor unit is equipped with high -- and low--pressure
switches. If the control senses the opening of a high-- or
low--pressure switch, it will respond as follows:
1. De--energize the appropriate compressor contactor.
2. Keep the outdoor fan operating for 15 minutes.
3. Display the appropriate fault code (see Table 6).
4. After a 15 minute delay, if there is a call for cooling or heat-
ing and LPS or HPS is reset, the appropriate compressor
contactor is energized.
5. If LPS or HPS has not closed after a 15 minute delay, the
outdoor fan is turned off. If the open switch closes anytime
after the 15 minute delay, then resume operation with a call
for cooling or heating.
6. If LPS or HPS trips 3 consecutive cycles, the unit operation
is locked out for 4 hours.
7. In the e vent of a high--pressure switch trip or high--pressure
lockout, check the refrigerant charge, outdoor fan operation,
and outdoor coil (in cooling) for airflow restrictions, or in-
door airflow in heating.
8. In the event of a low--pressure switch trip or low--pressure
lockout, check the refrigerant charge and indoor airflow
(cooling) and outdoor fan operation and outdoor coil in
heating.
Control Fault
If the outdoor unit control board has failed, the control will flash
the appropriate fault code (see Table 6). The control board should
be replaced.
Brown--Out Protection
If the line voltage is less than 187v for at least 4 seconds, the
appropriate compressor contactor and fan relay are de--energized.
Compressor and fan operation are not allowed until voltage is a
minimum of 190v. The control will flash the appropriate fault code
(see Table 6).
230v Brown--Out Protecti on Defeated
The brownout feature can be defeated if needed for severe noisy
power conditions. This defeat should always be a last resort to
solving the problem. Defeat is available on the User Interface
setup screen (available with SYSTXBBUID01--C UI) or can be
initiated through the forced defrost pins for non--communicating
systems as follows:
The brownout toggle is accomplished by shorting t he defrost pins
from power up with the OAT and OCT sensor connector removed.
After 3 seconds, the status of the force defrost short and the
OAT/OCT as open will be checked. If correct, then the brownout
will be toggled.
S Status code6 shows thebrownout isdisabled.
S Status code5 shows thebrownout isactive.
After the brownout defeat is set, power down and reinstall the
OAT/OCT sensor and remove the short from the forced defrost
pins. As long as the short on the forced defrost remains, the OAT
286A / 288A