070.610-IOM (JUL 21)
Page 46
RWF II Rotary Screw Compressor Units
Maintenance
EZ-CAL High pressure cut-out check
valve test block
The optional Frick
EZ-CAL
™
test block may be installed on
the package and can be used for the periodic testing and
calibration of the high discharge pressure limiting device
(High Pressure Cut-out, or HPCO).
This block is installed near the Quantum HD electronic
controller and contains the discharge pressure transducer
(connected to the electronic controller as a HPCO). This
block is factory installed on the package, the pressure
transducer is wired to the Quantum HD controller and
tubing is run to the compressor discharge connection (See
pages 51 and 54 for diagrams).
The block can be locked in the
RUN
position during normal
operation, but the compressor is still protected from a
high pressure event in either operational position.
EZ-Cal principles of operation
The test block functions as a low pressure drop check
valve, not a stop valve, in the line from the discharge
pressure source to the HPCO. In the
RUN
position the
HPCO is fully open to the discharge pressure source.
In the
TEST
position an external pressure source is con-
nected to the test connection quick connect and when the
valve is switched to
TEST
position, the external source is
connected directly to the HPCO. This allows the func
-
tion of the HPCO and pressure setting to be confirmed
by application of external pressure while comparing the
compressor discharge pressure reading to a master gauge.
Once the HPCO is confirmed to trip the compressor at the
correct set point, the valve is switched back to run mode
and any high pressure trapped above the check valve is
relieved back to the system. Should an actual high pres
-
sure event occur, even during testing, the check valve in
the test block will open and expose the HPCO to the high
pressure level, still allowing protection of the compressor
during testing of the HPCO.
NOTICE
Leaving the test block valve in the TEST position af-
ter testing is complete can trap the external pressure
between the HPCO and the test port.
Leaving the test block valve in the
TEST
position after
testing is complete risks trapping the external pres
-
sure between the HPCO and the test port. The discharge
pressure reading on the control panel would not see the
decrease in discharge pressure as the system is returned
to normal operation. Returning the test block valve to
the RUN position after testing opens a direct two-way
connection between discharge pressure and the HPCO
transducer or switch.
Refer to
160.100-IO
for the full operation procedure and
more detail on the EZ-CAL
™
Test Block and Test Pump
Calibration Kit.
Pressure transducers – testing
1.
Shut down the compressor and allow pressures to
equalize.
2.
Isolate suction transducer PE-4 from the unit and
depressurize. Ensure that the transducer has proper volt-
age for excitation. Measure across the red and black wires
(power and DC common) of the transducer. Voltage should
be 11.8 VDC to 15 VDC.
NOTICE
Recover or transfer all refrigerant vapor, in ac-
cordance with local ordinances, before opening to
atmosphere.
3.
Measure the voltage of PE-4 on connector P6A (ter
-
minals WHT and BLK) on the Analog Board with a digital
voltmeter.
4.
The
voltage reading should be 1.48 VDC to 1.72 VDC at
standard atmospheric pre
ssure (14.7 psia or 0 psig). When
checking transducers at higher elevations, an allowance
in the readings must be made by subtracting approxi
-
mately 0.02 VDC per 1000 ft of elevation above sea level.
Therefore, if PE-4 is measured at 5000 ft elevation under
relatively normal weather conditions, the output voltage
should differ by 0.10 VDC to read between 1.38 VDC and
1.62 VDC.
5.
Isolate the oil pressure transducer PE-1 from the pack-
age and open it to atmosphere.
6.
Measure the voltage of PE-1 on connector P5A (termi
-
nals WHT and BLK) on the Analog Board.
7.
The voltage reading should be between 1.1 VDC and
1.29 VDC at standard atmospheric pressure. PE-1, PE-2,
and PE-3 all have a span of 500 psi as compared to PE-4
with a span of 200 psi. As a result, atmospheric pres-
sure changes have a lesser effect which is 0.0067 VDC
per 1000 ft of elevation and 0.00067 VDC per 0.1 in. Hg
barometric deviation.
8.
Isolate transducer PE-2 from the package and depres
-
surize.
NOTICE
Recover or transfer all refrigerant vapor, in ac-
cordance with local ordinances, before opening to
atmosphere.
9.
Measure the voltage of PE-2 on connector P5B (termi
-
nals WHT and BLK) on the Analog Board.
10.
The voltage reading should be between 1.1 VDC and
1.29 VDC at standard atmospheric pressure (see Step 12).
11.
Since the
discharge pressure, PE-3, cannot be closed
off from its sensing point (code require ments), close all
transducers from atmosphere and open them to their
sensing points so all transducers can equalize to separator
pressure.
12.
Measure the voltage of PE-3 on connector P5B (termi
-
nals WHT and BLK) on the Analog Board.
13.
Measure the voltage of PE-1 on connector P5A (termi
-
nals WHT and BLK) on the Analog Board.