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5.5
Charging procedure
It is considered good practice when charging a system to charge liquid refrigerant into the high
side and vapour charge the low side of the system.
An alternative method is for liquid to be charged through the liquid receiver shut-off valve or
through a valve in the liquid line.
The use of a filter drier in the charging line is highly recommended.
It is not good for any compressor to have liquid refrigerant dumped from a refrigerant cylinder
into the crankcase of the compressor.
Rotation direction
5.6
Scroll compressors, like several other types of compressors, will only compress in one rotational
direction. Three-phase compressors will rotate in either direction depending upon phasing of the
power. Since there is a 50-50 chance of connecting power in such a way as to cause rotation in
the reverse direction, it is important to include notices and instructions in appropriate
locations on the equipment to ensure proper rotation direction when the system is
installed and operated.
Observing that suction pressure drops and discharge pressure rises when the compressor is
energized allows verification of proper rotation direction. There is no negative impact on
durability caused by operating three-phase Copeland Scroll
direction for a short period of time (under one hour) but oil may be lost. Oil loss can be prevented
during reverse rotation if the tubing is routed at least 15 cm above the compressor. After several
minutes of operation in reverse, the compressor protection system will trip due to high motor
temperature. The operator will notice a lack of cooling. However, if allowed to repeatedly restart
and run in reverse without correcting the situation, the compressor will be permanently
damaged.
All three-phase scroll compressors are identically wired internally. Therefore, once the correct
phasing is determined for a specific system or installation, connecting properly phased power
leads to the identified compressor terminals will ensure proper rotation direction.
Minimum run time
5.7
There is no set answer to how often scroll compressors can be started and stopped in an hour,
since it is highly dependent on system configuration. There is no minimum off time because
scroll compressors start unloaded, even if the system has unbalanced pressures. The most
critical consideration is the minimum run time required to return oil to the compressor after start-
up. To establish the minimum run time obtain a sample compressor equipped with a sight glass
(available from Copeland) and install it in a system with the longest connecting lines that are
approved for the system. The minimum on time becomes the time required for oil lost during
compressor start-up to return to the compressor sump and restore a minimal oil level that will
ensure oil pick-up through the crankshaft. Cycling the compressor for a shorter period than this,
for instance to maintain very tight temperature control, will result in progressive loss of oil and
damage to the compressor.
Pump-down cycle
5.8
A pump-down cycle may be used for control of refrigerant migration. If a pump-down cycle is
used, a separate external check valve must be added to the discharge line to prevent liquid
refrigerant from returning to the compressor through the discharge line and also to prevent
frequent recycling due to leak-back. The internal scroll discharge check valve is designed to stop
extended reverse rotation and prevent-high pressure gas from leaking rapidly into the low side
after shut off.
If a microprocessor is used, the system can be set to pump down for a fixed number of seconds
after the set point is reached and the liquid line solenoid valve is closed. The system should
pump down until the pressure is close to the cut out pressure of the low-pressure switch. It is not
C6.2.7/0302-1007/E
TM
compressors in the reversed
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