Johnson Controls York YK - Condenser and Evaporator Maintenance

035-19569-101 (0109)
7-5
GB
7.4.4 Refrigerant Charging
NOTE
When opening any part of the refrigerant
system for repairs, the refrigerant charge
must be removed. If the chiller is equipped
with optional valves, the refrigerant can be
isolated in either the condenser or evaporator
/ compressor while making repairs.
To prevent liquid freezing within the evaporator tubes
when charging an evacuated system, only refrigerant
vapour must be added to the system until the system
pressure is raised above the point corresponding to the
freezing point of the evaporator liquid. For water, the
pressure corresponding to the freezing point is 58.9 kPa
for R134a (at sea level).
NOTE
While charging, care must be taken to prevent
moisture laden air from entering the system.
Make up a suitable charging connection from new
copper tubing to fi t between the system charging valve
and the fi tting on the charging drum. This connection
should be as short as possible but long enough to permit
suffi cient fl exibility for changing drums. The charging
connection should be purged each time a new container
of refrigerant is connected and changing containers
should be done as quickly as possible to minimise the
loss of refrigerant.
Refer to Section 9.2 for details of refrigerant charge
weights.
7.5 Condenser and Evaporator
The major portion of maintenance on the condenser
and evaporator is maintaining the water side of the
condenser and evaporator in a clean condition.
The use of untreated water in cooling towers, closed
water systems, etc. frequently results in one or more of
the following:
1. Scale Formation.
2. Corrosion or Rusting.
3. Slime and Algae Formation.
It is therefore to the benefi t of the user to provide for
proper water treatment to provide for a longer and
more economical life of the equipment. The following
recommendation should be followed in determining
the condition of the water side of the condenser and
evaporator tubes.
1. The condenser tubes should be cleaned annually
or earlier if conditions warrant. If the temperature
difference between the water off the condenser and
the condenser liquid temperature is more than 2.2 K
greater than the difference recorded on a new unit, it
is a good indication that the condenser tubes require
cleaning.
2. The evaporator tubes under normal circumstances
will not require cleaning. If however the temperature
difference between the refrigerant and the chilled
water increases slowly over the operating season,
it is an indication that the evaporator tubes may be
fouling or that there may be a water by-pass in the
water box requiring gasket replacement or refrigerant
may have leaked from the chiller.
7.5.1 Chemical Water Treatment
Since the mineral content of the water circulated through
the evaporator and condenser varies with almost every
source of supply, it is possible that the water being used
may corrode the tubes or deposit heat resistant scale in
them. Reliable water treatment 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 water
treatment expert should be consulted to determine
whether water treatment is necessary, and if so, to
furnish the proper treatment for the particular water
condition.
7.5.2 Tube Cleaning
Evaporator
It is diffi cult to determine by any particular test whether
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 difference
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.