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Discharge thermostat
ZF models (up to ZF18) have an external discharge thermostat which controls the discharge temperature.
The thermostat cut-off point is
The cut-in differential is 28 K +/- 5 K
The crankcase heater must be powered and operational during compressor shut-downs.
AUTOMATIC MECHANICAL DEVICES
As we do not design the installation, we are responsible only for the electrical layout and refrigeration equipment.
Nevertheless, we recommend:
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providing a pump down or pump out control to close the system down
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providing for an automatic closure of one or more refrigerant fluid solenoid
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providing condenser pressure control by cycling the fans.
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connecting internal thermal protection for compressor motors.
8-
START-UP OPERATIONS
PRELIMINARY CHECKS AND OPERATIONS
General information
Ensure that all the threads are fully tightened on connection flanges, flexible connections and cables.
jolting during transport could cause screws and bolts to loosen.
Check also, for same reasons, if there are any breaks in the piping.
Ensure that the flexible connections are not in contact with metal parts. Vibrations from the compressor can cause wear in these
until they rupture at the point of friction.
Switch on crankcase heaters 24 hours before start-up.
Before starting up a machine with pressurised tanks, all service valves must first be opened upstream and downstream and all
external valves closed..
Check that the condenser fans turn freely.
Determining the compressor rotation direction
Important:
Scroll compressors only have one rotation direction. Any rotation in the opposite sense may lead to a compressor
destruction.
During the first start up, it is absolutely necessary to determine the phases connections to compressor terminals. That handling
must be tactful with hermetic compressors and must be extremely fast.
- Place a LP pressure gauge at the compressor suction or on the header.
- Start up the compressor with the start button
- As soon as it is started, stop the compressor.
- During that time, if the pressure gauge showed that the pressure went down, the rotation direction is correct.
- In the opposite case, invert the 2 phases on the compressor breaker and repeat the same operation for checking.
NB: We advise you to include a rotation direction detector in your electrical diagrams.
Leakage
testing
Pressurise the whole system using a neutral gas (Nitrogen R) with a (non-liquid, non-colouring) tracer, at a minimum pressure of 10
bars and at a maximum pressure of less than 20.5 bars, isolating the LP (low pressure) switches.
Important
: If the LP circuit is fitted with a safety valve (e.g.: on the suction accumulator) the test pressure on that part of the
circuit should be approx. 20% below the operating pressure of this valve.
Thorough leakage detection using a suitable detector should be carried out on the condensing unit.
After these tests, the gas must be removed. Fit the dryer cartridges in their casing.
Dehydrationof circuits
This operation must be carried out with all valves open (including solenoid valves) with connection to a vacuum pump:
of the low pressure side
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of the high pressure side
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The quality of drying should not be judged by the speed at which the level of vacuum is reached but on the effective time
it is held (24 hours at 0.7 mbar is a good standard).
The total increase in pressure during that period should not be more than 2.6 mbar. The residual moisture in the system should be
less than 20ppm.
When the installation is under vacuum, an insulation check of the motor should not be carried out nor should the compressors be
started before at least 1 bar of fluid pressure is reintroduced.
This is to prevent motor winding damage.
99°C +/- 4 K
valves during a safety cut-out on the compressor.
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