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System Operation
Some scroll compressor have internal vacuum protector
that will unload scrolls when suction pressure goes
below 20 psig. A hissing sound will be heard when the
compressor is running unloaded. Protector will reset
when low pressure in system is raised above 40 psig. DO
NOT REPLACE COMPRESSOR.
The Main Control provides the following system functions:
S
Compressor anti−short−cycle delay.
S
High and low pressure switches
S
Ambient and Discharge Line Temperatures Monitoring
and Protection.
S
Five strikes lockout safety feature for High/Low
Pressure
Switches
Temperature. See Figures 19, 20 and 21 feature
function.
COMPRESSOR ANTI−SHORT CYCLE DELAY
The Main Control protects the compressor from:
S
Short cycling (five minutes) when there is initial power
up
S
Interruption in power to the unit
S
High or low pressure switch or discharge line sensor
trips
S
Delay after Y1 demand is removed.
The anti−short timer in the outdoor control is 5 minutes. To
override timer when active or inactive − place jumper on the
field test pins between 1 and 2 seconds.
Resetting Anti−Short Cycle Delay
The FIELD TEST pins (E33) on the Main Control can be
jumpered between 1 to 2 seconds to bypass delay.
HIGH AND LOW PRESSURE SWITCHES
The unit's reset pressure switches LO PS (S4) and HI PS
(S87) are factory−wired into the Main Control on the LO−PS
and HI−PS terminals, there locations are illustrated on
Page 3. Sequence of operations for both pressure
switches are provided in Figures 19 and 20.
HIGH DISCHARGE LINE TEMPERATURE
(RT28)
The high discharge line temperature sensor location is
illustrated on Page 3. This sensor's sequence of
operations is provided in Figure 21.
High Discharge Line Sensor Open/Shorted Event
Discharge sensor open / short fault is ignored during initial
90−seconds of compressor run time. After that, if discharge
temperature sensor is detected open or short, the control
will de−energize all the outputs and anti−short cycle timer is
started. Discharge sensor faulty alert LED code will be
displayed.
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and High Discharge Line
Condition
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OUTDOOR AMBIENT TEMPERATURE (RT13)
If the outdoor ambient temperature sensor detected a
open, or out of range −40ºF to +140ºF (−40ºC to 60ºC) then
LED alert codes are displayed, however cooling operation
will continue. See Table 9 for LED alert codes for the
ambient sensor. Location of outdoor ambient temperature
sensor is illustrated on Page 3.
COIL TEMPERATURE SENSOR
This model does not use a coil temperature sensor. The
cable assembly attached to the Main Control's E30
connection has a 10K resister installed between pins 5 and
6 as illustrated in Figure 17. No alerts or alarms would be
generated if resistor is damage.
Ambient Air
Temperature Sensor
High Discharge Line
Temperature Sensor
TESTING AMBIENT AND HIGH DISCHARGE LINE
TEMPERATURE SENSORS
Sensors connect through a field-replaceable harness
assembly that plugs directly into the Main Control.
Through these sensors, the Main Control can monitor
outdoor ambient and discharge line temperature fault
conditions. As the detected temperature changes, the
resistance across the sensor changes. Figures 6 and 7
lists how the resistance varies as the temperature changes
for both type of sensors. Sensor resistance values can be
checked by ohming across pins shown in Table 8.
When a sensor indicates a resistance value that is not
within the range as listed in Table 8, then the following
condition may be present:
SENSOR
S
Sensor detects an out−of−range outdoor ambient air
temperature condition and will display LED alert code
on the Main Control.
S
The sensor is operating normally when the ambient air
temperature at the sensor is below or above the Main
Control's expected ohm values. The Main Control will
indicate the sensor as faulty, however under this
scenario, the sensor is not actually faulty.
S
Once the outdoor ambient air temperature has
returned to within the sensor's normal operating
range, the LED alert code will automatically stop.
Page 31
Figure 17. 10k Resistor Location
10K resistor
XC17 SERIES
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