York YD A, Operating & Maintenance, Page: 45 / 52

JOHNSON CONTROLS
45
SECTION 6 – MAINTENANCE
FORM 160.69-O2
ISSUE DATE: 9/30/2020
6
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
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-
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 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-
ly clean each tube with a soft bristle bronze or nylon
brush. DO NOT USE A STEEL BRISTLE BRUSH .
A steel brush may damage the tubes.
Improved results can be obtained by admitting water
into the tube during the cleaning process. This can be
done by mounting the brush on a suitable length of 1/8"
pipe with a few small holes at the brush end and con-
necting the other end by means of a hose to the water
supply.
The tubes should always be brush cleaned before acid
cleaning.