SD-324M / Page 9
LABEL COLOR
Prng
PSI
Green
150
(v-.5) x 37.5
None / Silver
300
(v-.5) x 75
Yellow
500
(v-.5) x 125
Figure 7 - Pressure Sensor Cable
Table 3 - Pressure Transducer Specifications
Troubleshooting Recommendations
As with any refrigeration component troubleshooting, actual
system conditions should be verified with a gauge set and a cali-
brated temperature sensor (i.e verify actual superheat and refriger-
ant condition). This system information is valuable in determining
whether it is component related or system related.
For systems or applications that experience light loads on the Kel-
vin II circuit, it is important that the heat exchanger and refrigerant
lines are sized correctly. This will ensure proper oil return and will
minimize the effects of oil logging in the heat exchanger. Many
heat exchanger manufacturers recommend a hot gas bypass for
loads below 50%.
Sensors
Failed sensors will trigger an alarm. An alarm code will show
which sensor is mis-wired, disconnected, or faulty. The alarm will
persist until the problem is corrected.
Failed temperature sensors
may read extremely low or infinite
resistance when tested with an ohmmeter. Readings should be
taken with the sensor disconnected from the Kelvin II. A missing
or disconnected temperature sensor will read
-60
on the controller.
Temperature sensor output can be checked by measuring the DC
voltage across the sensor wires and consulting the tables in
Appendix K and Appendix L.
2K and 3K sensors have approximately 1.9KΩ and 2.8KΩ,
respectively, at 80̊F measured across sensor wires.
Pressure transducers
must be installed tight enough to depress
the valve stem in the fitting. Failure to do so will result in errone-
ous pressure readings and possibly leaks.
Pressure transducers should be tested while connected to the
controller and powered. Test at the controller terminals. Voltage
between terminals 34
and 35
should be 4.8 - 5.2 volts DC. Voltage
between 33 and 34 should be between 0.5 and 4.5 volts DC.
See Table 1 - Pressure Transducer Wire Colors.
To test the accuracy of the transducer, use a gauge set to obtain the
actual system pressure. For volts-to-pressure conversion, measure
the voltage between terminals 33 and 34. Identify the pressure
transducer used and find the correct range
Prng
in Table 3.
Substitute the measured voltage (v) into the formula in the PSI
column. The result should be within 3 psi of the actual system
pressure shown on the gauge set. If not, check the transducer for
proper installation, correct Schrader valve, and verify the pressure
range identified on the transducer.
To test the transducer cable, disconnect the cable from the trans-
ducer and check for 4.8 - 5.2 volts between terminals
+
and
–
.
See Figure 7 - Pressure Sensor Cable.
ALARMS
If the superheat is 2 degrees below setpoint for 30 seconds, the
controller will display the alarm
LSHA
.
Alarms will persist until the problem is corrected.
ALARM DESCRIPTION
ACTION
PSAL
Pressure Sensor
Failure
Pumpdown (open terminals
19 & 20) and close EEV
tSAL
Suction Temp
Sensor Failure
Pumpdown (open terminals
19 & 20) and close EEV
LSHA
Low Superheat
If superheat is 2 degrees or less,
EEV will close more aggressively
HSHA
High Superheat
No system response
Table 4 - Alarm Actions