Keep the exterior surface of the tubes and the finson an air-cooled condenser free of dirt or any matter thatmight obstruct heat flow and air circulation. The finnedsurface should be brushed clean with a stiff bristle brushas often as necessary. Low-pressure air is very useful inremoving dirt in hard-to-reach places on condensers.When installations are exposed to salt spray and rainthrough open doors or hatches, you should take steps tominimize corrosion of the exterior surfaces.Testing For LeaksTo prevent serious loss of refrigerant through leakycondenser tubes, test the condenser for leakage byfollowing the PMS.To test for leaky condenser tubes, drain thewaterside of the condenser. Then insert the exploringtube of the leak detector through one of the drain plugopenings. If this test indicates that Freon gas is present,you can find the exact location of the leak by followingthese steps:1. Remove the condenser heads.2. Clean and dry the tube sheets and the ends of thetubes.3. Check both ends of each tube with a leakdetector. Mark any tubes that show leakage. If youcannot determine that a tube is leaking internally oraround the tube sheet joint, plug the suspected tube andagain check around the tube sheet joint. Mark theadjacent tube, if necessary, to isolate the suspected area.4. To locate or isolate very small leaks in thecondenser tubes, hold the exploring tube at one end ofthe condenser tube for about 10 seconds to draw freshair through the tube. Repeat this procedure with all thetubes in the condenser. Allow the condenser tubes toremain plugged for 4 to 6 hours; then, remove the plugsone at a time and check each tube for leakage. If a leakytube is detected, replace the plug immediately to reducethe amount of refrigerant escaping. Make appropriaterepairs or mark and plug all leaky tubes for later repairs.Plugging or Retubing CondensersThe general procedures for plugging or retubingcondensers can be found in Naval Ship's TechnicalManual (NSTM), Chapter 254, “Condensers, HeatExchangers, and Air Ejectors.”When plugging orretubing a specific condenser, follow the procedures inthe manufacturer’s technical manual.THERMOSTATIC EXPANSION VALVESThe thermostatic expansion valve is essentially areducing valve between the high-pressure side and thelow-pressure side of the system. The valve is designedto proportion the rate at which the refrigerant enters thecooling coil to the rate of evaporation of the liquidrefrigerant in the coil; the amount depends, of course,on the amount of heat being removed from therefrigerated space.When the thermostatic expansion valve is operatingproperly, the temperature at the outlet side of the valveis much lower than that at the inlet side. If thistemperature difference does not exist when the systemis in operation, the valve seat is probably dirty andclogged with foreign matter.Once a valve is properly adjusted, furtheradjustment should not be necessary. The major troublecan usually be traced to moisture or dirt collecting at thevalve seat and orifice.Testing and AdjustmentThe thermostatic expansion valves used in mostshipboard systems can be adjusted by means of a gearand screw arrangement to maintain a superheat rangingfrom about 4°F to 12°F at the cooling coil outlet. Theproper superheat adjustment varies with the design andservice operating conditions of the valve and the designof the particular plant. Increased spring pressureincreases the degree of superheat at the coil outlet.Decreased spring pressure decreases the degree ofsuperheat at the coil outlet.Some thermostatic expansion valves have a fixed(nonadjustable) superheat. These valves are usedprimarily in self-contained equipment where the pipingconfiguration and evaporating conditions are constant.If expansion valves are adjusted to give a highsuperheat at the coil outlet or if the valve is stuck shut,the amount of refrigerant admitted to the cooling coilwill be reduced. With an insufficient amount ofrefrigerant, the coil will be “starved” and will operate ata reduced capacity. Also, the velocity of the refrigerantthrough the coil may not be adequate to carry oil throughthe coil. This robs the compressor crankcase andprovides a condition where slugs of lubricating oil maybe drawn back into the compressor. If the expansionvalve is adjusted for too low a degree of superheat or ifthe valve is stuck open, liquid refrigerant may floodfrom the cooling coils back into the compressor. Whenliquid refrigerant collects at a low point in the suction5-7
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