Handling Refrigerant For Dismantling And Repairs; Megging The Motor - York R-134a Operation And Maintenance Manual

SECTION 6 - MAINTENANCE
HANDLING REFRIGERANT FOR
DISMANTLING AND REPAIRS
If it becomes necessary to open any part of the refriger-
ant system for repairs, it will be necessary to remove
the charge before opening any part of the unit. If the
chiller is equipped with optional valves, the refrigerant
can be isolated in either the condenser or evaporator /
compressor while making any necessary repairs.

MEGGING THE MOTOR

While the main disconnect switch and compressor mo-
tor starter are open, meg the motor as follows:
1. Using a megohm meter (megger), meg between
phases and each phase to ground (See Figure 13 on
page 26); these readings are to be interpreted us-
ing the graph shown in Figure 14 on page 27.
2. If readings fall below shaded area, remove exter-
nal leads from motor and repeat test.
Motor is to be megged with the starter at
ambient temperature after 24 hours of
idle standby.
Condensers And Evaporators General
Maintenance of condenser and evaporator shells is im-
portant to provide trouble free operation of the chiller.
The water side of the tubes in the shell must be kept
clean and free from scale. Proper maintenance such as
tube cleaning, and testing for leaks, is covered on the
following pages.
Chemical Water Treatment
Since the mineral content of the water circulated
through evaporators and condensers varies with almost
every source of supply, it is possible that the water be-
ing used may corrode the tubes or deposit heat resistant
scale in them. Reliable water treatment companies are
available in most larger cities to supply a water treat-
ing process which will greatly reduce the corrosive and
scale forming properties of almost any type of water.
As a preventive measure against scale and corrosion and
to prolong the life of evaporator and condenser tubes, a
chemical analysis of the water should be made prefer-
ably before the system is installed. A reliable water treat-
ment company can be consulted to determine whether
water treatment is necessary, and if so, to furnish the
proper treatment for the particular water condition.
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Cleaning Evaporator And Condenser Tubes
Evaporator
It is difficult to determine by any particular test wheth-
er possible lack of performance of the water evaporator
is due to fouled tubes alone or due to a combination
of troubles. Trouble which may be due to fouled tubes
is indicated when, over a period of time, the cooling
capacity decreases and the split (temperature differ-
ence between water leaving the evaporator and the
refrigerant temperature in the evaporator) increases. A
gradual drop-off in cooling capacity can also be caused
by a gradual leak of refrigerant from the system or by a
combination of fouled tubes and shortage of refrigerant
charge. An excessive quantity of oil in the evaporator
can also contribute to erratic performance.
Condenser
In a condenser, trouble due to fouled tubes is usually
indicated by a steady rise in head pressure, over a pe-
riod of time, accompanied by a steady rise in condens-
ing temperature, and noisy operation. These symptoms
may also be due to foul gas buildup. Purging will re-
move the foul gas revealing the effect of fouling.
Tube Fouling
Fouling of the tubes can be due to deposits of two types
as follows:
1. Rust or sludge – which finds its way into the
tubes and accumulates there. This material usu-
ally does not build up on the inner tube surfaces
as scale, but does interfere with the heat transfer.
Rust or sludge can generally be removed from the
tubes by a thorough brushing process.
2. Scale – due to mineral deposits. These deposits,
even though very thin and scarcely detectable
upon physical inspection, are highly resistant to
heat transfer. They can be removed most effec-
tively by circulating an acid solution through the
tubes.
Tube Cleaning Procedures
Brush Cleaning of Tubes
If the tube consists of dirt and sludge, it can usually be
removed by means of the brushing process. Drain the
water sides of the circuit to be cleaned (cooling wa-
ter or chilled water) remove the heads and thorough-
FORM 160.76-O1
ISSUE DATE: 05/22/2019
JOHNSON CONTROLS