Handling Refrigerant For Dismantling And Repairs; Megging The Motor; Condensers And Evaporators; General - York YMC2 A Operation And Maintenance

Form 160.78-O1
Issue date: 05/19/2021
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 refriger-
ant can be isolated in either the condenser or in the
evaporator or compressor while making any necessary
repairs.

Megging the motor

Electrical test of motor winding resistance should be
performed by a qualified service technician because
it involves determination of power leads between the
motor and the VSD. Results from these winding insu-
lation resistance tests should be trended each interval
to determine degradation in motor windings.

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. Correct maintenance proce-
dures 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
preferably before the system is installed. A reliable wa-
ter treatment company can be consulted to determine
whether water treatment is necessary, and if so, to fur-
nish the proper treatment for the particular water con-
JOHNSON CONTROLS
dition.

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 refriger-
ant charge.
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.

Tube fouling

Fouling of the tubes can be due to the following types
of deposits:
1. Rust or sludge – which finds its way into the tubes
and accumulates there. This material usually 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 effectively by
circulating an acid solution through the tubes.
Section 3 - Maintenance
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