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Troubleshooting the Suction Pressure Transducer
0-250 psig
-5v Nominal .5 – 4.5v Actual
4v/250 psig = .016 volts per 1 psig
Example: 125 psig x .016 + .5 volts = 2.5 volts
Formula for Tech:
Measured Pressure x .016 + Sensor Offset = Expected
Transducer Signal Voltage (see Figure 28).
FIGURE 28
Voltage to Pressure: Suction Pressure Transducer
Suction Pressure Alarm
When the suction pressure transducer value is out
of range (0-250 PSIG), the controller will generate
a sensor failure alarm to indicate the sensor is not
working properly.
This alarm cannot be adjusted.
Suction Temperature Sensor
The suction temperature sensor is used to calculate
superheat. The EEV uses this value to control the EEV.
The temperature is measured with a 10k ohm NTC
thermistor.
The suction temperature sensor measurement can be
verified and adjusted by:
1. Press MENU key to go to the Main Menu screen.
2. Press UP or DOWN keys and ENTER key to enter
TECHNICIAN password 1313.
3. Press UP or DOWN keys to scroll to I/O Config;
press ENTER key.
4. Press UP or DOWN keys to scroll to Suct Temp
Sensor C8.
5. Verify the measurement displayed on screen is
accurate (see Figure 29).
6. If the measurement needs to be adjusted, apply an
offset value by pressing ENTER to scroll to Offset.
7. Press UP or DOWN keys to adjust the offset.
8. The update will not take effect until the cursor is
moved out of the Offset parameter.
FIGURE 29
Adjusting Suction Temperature Sensor Values
Suction Temperature Alarm
When the suction temperature sensor value is out of
range (-41.0 to 303.0°F), the controller will generate
a sensor failure alarm to indicate the sensor is not
working properly.
This alarm cannot be adjusted.
Evaporator Freeze Condition Alarm
The freeze alarm (evaporator coil freeze protection)
uses the suction temperature sensor to alarm and
manage operation when conditions are favorable for
an evaporator coil freeze condition. Whenever the
compressor is running, the system will constantly
monitor the suction line temperature. If the suction
line temperature falls below the freeze setpoint (32°F
factory default) for a period of time exceeding freeze
alarm delay time (120 seconds factory default), the
system will alarm a freeze condition. Once a freeze
condition is triggered, the system will stop the
compressor operation and increase the blower speed to
80% in order to rapidly warm and thaw the evaporator
coil. After the coil has reached a temperature above the
freeze alarm reset temperature setpoint (55°F factory
default) for a period of time exceeding the freeze alarm
reset hold time (5 minutes factory default), normal
operation will continue.
To adjust the freeze setpoint and/or alarm delay time:
1. Press MENU key to go to the Main Menu screen.
2. Press UP or DOWN keys and ENTER key to enter
USER password 2000.
3. Press UP or DOWN keys to scroll to System Config;
press ENTER key.
4. Press UP or DOWN keys to scroll to Alarm Setup
A7.
5. Press ENTER key to scroll to Alarm Setpoint (see
Figure 30 on page 20).
6. Press UP or DOWN keys to change to the desired
value.
7. Press ENTER key to save the value and move
cursor to Alarm Delay.
Manual 2100-695C
Page
19 of 56
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