Keep the exterior surface of the tubes and the fins
on an air-cooled condenser free of dirt or any matter that
might obstruct heat flow and air circulation. The finned
surface should be brushed clean with a stiff bristle brush
as often as necessary. Low-pressure air is very useful in
removing dirt in hard-to-reach places on condensers.
When installations are exposed to salt spray and rain
through open doors or hatches, you should take steps to
minimize corrosion of the exterior surfaces.
Testing For Leaks
To prevent serious loss of refrigerant through leaky
condenser tubes, test the condenser for leakage by
following the PMS.
To test for leaky condenser tubes, drain the
waterside of the condenser. Then insert the exploring
tube of the leak detector through one of the drain plug
openings. If this test indicates that Freon gas is present,
you can find the exact location of the leak by following
1. Remove the condenser heads.
2. Clean and dry the tube sheets and the ends of the
3. Check both ends of each tube with a leak
detector. Mark any tubes that show leakage. If you
cannot determine that a tube is leaking internally or
around the tube sheet joint, plug the suspected tube and
again check around the tube sheet joint. Mark the
adjacent tube, if necessary, to isolate the suspected area.
4. To locate or isolate very small leaks in the
condenser tubes, hold the exploring tube at one end of
the condenser tube for about 10 seconds to draw fresh
air through the tube. Repeat this procedure with all the
tubes in the condenser. Allow the condenser tubes to
remain plugged for 4 to 6 hours; then, remove the plugs
one at a time and check each tube for leakage. If a leaky
tube is detected, replace the plug immediately to reduce
the amount of refrigerant escaping. Make appropriate
repairs or mark and plug all leaky tubes for later repairs.
Plugging or Retubing Condensers
The general procedures for plugging or retubing
condensers can be found in Naval Ship's Technical
Manual (NSTM), Chapter 254, Condensers, Heat
Exchangers, and Air Ejectors.
When plugging or
retubing a specific condenser, follow the procedures in
the manufacturers technical manual.
THERMOSTATIC EXPANSION VALVES
The thermostatic expansion valve is essentially a
reducing valve between the high-pressure side and the
low-pressure side of the system. The valve is designed
to proportion the rate at which the refrigerant enters the
cooling coil to the rate of evaporation of the liquid
refrigerant in the coil; the amount depends, of course,
on the amount of heat being removed from the
When the thermostatic expansion valve is operating
properly, the temperature at the outlet side of the valve
is much lower than that at the inlet side. If this
temperature difference does not exist when the system
is in operation, the valve seat is probably dirty and
clogged with foreign matter.
Once a valve is properly adjusted, further
adjustment should not be necessary. The major trouble
can usually be traced to moisture or dirt collecting at the
valve seat and orifice.
Testing and Adjustment
The thermostatic expansion valves used in most
shipboard systems can be adjusted by means of a gear
and screw arrangement to maintain a superheat ranging
from about 4°F to 12°F at the cooling coil outlet. The
proper superheat adjustment varies with the design and
service operating conditions of the valve and the design
of the particular plant. Increased spring pressure
increases the degree of superheat at the coil outlet.
Decreased spring pressure decreases the degree of
superheat at the coil outlet.
Some thermostatic expansion valves have a fixed
(nonadjustable) superheat. These valves are used
primarily in self-contained equipment where the piping
configuration and evaporating conditions are constant.
If expansion valves are adjusted to give a high
superheat at the coil outlet or if the valve is stuck shut,
the amount of refrigerant admitted to the cooling coil
will be reduced. With an insufficient amount of
refrigerant, the coil will be starved and will operate at
a reduced capacity. Also, the velocity of the refrigerant
through the coil may not be adequate to carry oil through
the coil. This robs the compressor crankcase and
provides a condition where slugs of lubricating oil may
be drawn back into the compressor. If the expansion
valve is adjusted for too low a degree of superheat or if
the valve is stuck open, liquid refrigerant may flood
from the cooling coils back into the compressor. When
liquid refrigerant collects at a low point in the suction