Hour Meters; Microprocessor Diagnostic Service Tool (Mdst); Control; Mode Keys - Carrier CAPRI-280 Operation And Service Manual

be disengaged when the system is off, when in heating
or during high and low pressure conditions.
The clutch coil is prevented from engagement when
the ambient temperature is below 45_F (7.2_C).
The clutch coil will be de-energized if the discharge
pressure rises to 300 psig, the setting of the
compressor mounted high pressure switch. The clutch
coil will energize when the discharge pressure falls to
200 psig.
The clutch coil will be de-energized if the suction
pressure decreases below 10 psig.
2.3.7 Alarm Description
Alarm descriptions and troubleshooting procedures
are provided in section 3.
2.3.8

Hour Meters

An hour meter records the compressor run time
hours. The maximum hours is 999,999.
(Refer to table 3-2)
An hour meter records the total time the evaporators
are on in hours. The maximum hours is 999,999.
(Refer to table 3-2)
2.4 MICROPROCESSOR DIAGNOSTIC
SERVICE TOOL (MDST)
The MDST is a diagnostic service tool that allows the
user to interface with the microprocessor based
control. This allows system parameters, alarms and
settings to be viewed and modified.
2.4.1 Connecting
Connect the MDST harness to the service port
located in the return air section of the A/C system.
When the MDST is connected, the panel lights will be
energized and the currently stored setpoint will be
displayed. If any alarm is active, the reading will be
Axx, where A indicates that the alarm is active and xx
indicates the alarm number.

2.4.2 Control

NOTE
This procedure should be performed by an
HVAC educated technician who knows the
Carrier Capri 280 system design. Control
configuration is preset
manufacturer and
parameters should not be required. It is
recommended that Carrier Service or
Engineering is contacted before any control
configuration is changed. Carrier can not be
responsible for changes made by the
customer which cause system failure if there
has not been an opportunity to approve the
changes.
a. Turn the A/C main switch located in the driver's
area to OFF.
T-283
in by the
resetting of the
b. Connect the MDST to the service port located in
the return air section.
c. Unplug the logic board connector J3.
d. Turn the A/C main switch located in the driver's
area back to the ON position.
e. Activate the system by pressing the 1/0 key on the
MDST panel.
NOTE
Be sure to reconnect J3 when testing is
completed or the system will fail to operate
when the MDST is disconnected.
2.4.3 Setpoint Change
Setpoint may be changed by pressing up or down
arrow keys. The up key will increase the setpoint
temperature and the down key will decrease the
setpoint temperature.
NOTE
When modifying the setpoint temperature
for diagnostic purposes, be sure to reset the
setpoint when testing is complete.

2.4.4 Mode Keys

The mode keys allow the operation to be selected as
auto, cool, heat, or vent. The default operation is auto
as shown in Figure 2-1.
2.4.4.1 Cool
The compressor is always operational in cool mode
unless overridden by safety device. Air conditioning
will run until setpoint is reached at which time the heat
valve will open and reheat is performed.
2.4.4.2 Heat
The compressor will not operate in heat mode. The
heat valve is opened until 1_F below setpoint at which
time the heat valve closes and the evaporator fans run
in ventilation.
2.4.4.3 Vent
In vent mode, only the evaporator fans operate.

2.4.5 Fan Key

The fan key allows the evaporator fan speed to be
overridden to high or low. The evaporator fan speed
will be reset to auto when auto mode key is pressed.
2.4.6 Temperature Key
The temperature key allows the actual return air
ambient temperatures to be displayed.

2.4.7 Diagnostic Mode

Diagnostic mode can be entered by pressing the up
and down arrow keys simultaneously for 5 seconds.
Diagnostic mode allows
parameters to be viewed. If there are any alarms
stored, the most recent alarm will be shown. To view
additional alarm information, refer to section 3. Press
the up and down arrow keys to view parameters.
2-4
alarms and system