FORM 160.77-O1
ISSUE DATE: 10/22/2020
JOHNSON CONTROLS
28
SECTION 3 - MAINTENANCE
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
other issues. Trouble which may be due to fouled tubes
is indicated when, over a period of time, the cooling
capacity decreases and the approach (temperature dif-
ference 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, and noisy operation. These symptoms
rarely may also be due to improper evacuation before
charging refrigerant during system breach.
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 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 most effec
-
tively by circulating an acid solution through the
tubes.
Tube Cleaning Procedures
Brush Cleaning of Tubes
If the tube fouling consists of dirt and sludge, it can
usually be removed by means of the brushing pro-
cess. Drain the water sides of the circuit to be cleaned
(cooling water or chilled water) remove the heads and
thoroughly 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.
Acid Cleaning of Tubes
Tubes that are fouled with a hard scale deposit, may re-
quire acid cleaning. The tubes should always be brush
cleaned before acid cleaning. If the relatively loose
foreign material is removed before the acid cleaning,
the acid solution will have less material to dissolve and
flush from the tubes resulting in a better cleaning job.
Acid cleaning should only be performed
by an expert. Please consult your local
water treatment representative for as-
sistance in removing scale buildup and
preventative maintenance programs to
eliminate future problems.
Commercial Acid Cleaning
In many major cities, commercial organizations now
offer a specialized service of acid cleaning evaporators
and condensers. If acid cleaning is required, Johnson
Controls recommends the use of this type of organiza-
tion. The Dow Industries Service Division of the Dow
Chemical Company, Tulsa, Oklahoma, with branches
in principal cities is one of the most reliable of these
companies.
COMPRESSORS
Maintenance for the compressor assembly consists of
the following checks:
• checking the operation of the oil return system
and changing the dehydrator
• checking and changing the oil
•
checking and changing the oil filters
• checking the operation of the oil heater
• checking the operation of the oil pump
• observing the operation of the compressor.
Internal wearing of compressor parts could be caused
by improper lubrication, brought about by restricted oil
lines, passages, or dirty oil filters. If the unit is shut-
ting down on High Oil Temperature (HOT) or Low Oil
Pressure (LOP), change the oil filter element. Exam-
ine the oil filter element for the presence of aluminum
