Figure 16-93. Damaged fins on a condenser. Figure 16-92.  This electronic infrared leak detector can detect leaks  that would lose less than ¼ ounce of refrigerant per year.  as can a f aulty expansion valve or feedback control line.  Ice formation anywhere on the outside of a vapor cycle air  conditioning system should be investigated for cause and  corrected.  [Figure 16-94] All components of any vapor cycle system should be checked  to ensure they are secure. Be vigilant for any damage,  misalignment, or visual signs of leakage. The evaporator and  condenser fins should be checked to ensure they are clean,  unobstructed, and not folded over from an impact. Dirt and  inhibited airflow through the fins can prevent effective heat  exchange to and from the refrigerant. Occasionally, these  units can be washed. Since the condenser often has ram  air ducted to it or extends into the airstream, check for the  presence of debris that may restrict airflow. Hinged units  should be checked for security and wear. The mechanism  to extend and retract the unit should function as specified,  including the throttle position switch present on many  systems. It is designed to cut power to the compressor clutch  and retract the condenser at full power settings. Condensers  may also have a fan to pull air over them during ground  operation. It should be checked to ensure it functions  correctly.  [Figure 16-93] Security and alignment of the compressor is critical  and should be checked during inspection. Belt-driven  com pressors nee d to have proper belt tension to function  properly. Check the manufacturer’s data for information  on how to  determine the condition and tension of the belt,  as well a how to make adjustments. Oil level should be  sufficient Typically,  1 ⁄ 4 ounce of oil is added for each  pound of refrigerant added to the system. When changing a  component, additional oil may need to be added to replace  that which is trapped in the replaced unit. Always use the oil  specified in the manufacturer’s maintenance manual. As  mentioned under the leak detector section above, leaks  in a vapor  cycle air conditioning system must be discovered  and repaired. The most obvious sign of a possible leak is a  low  refrigerant level. Bubbles present in the sight glass of the  receiver  dryer while the system is operating indicate more  refrigerant  is needed. A system check for a leak may be in  order. Note that vapor cycle systems normally lose a small  amount of refrigerant each year. No action is needed if this  amount is within limits.  Occasionally, all of the refrigerant escapes from the system.  No bubbles are visible in the sight glass, but the complete  lack of cooling indicates the refrigerant has leaked out. To  locate the  leak point, the system needs to be partially charged  with refrigerant so leak detection methods can be employed.  Be sure the capillary temperature feedback sensor to the  expansion valve is securely attached to the evaporator outlet.  Also, check the security of the pressure sensor and thermostat  sensor if the system has them. The evaporator should not  have ice on the outside. This prevents proper heat exchange  to the refrigerant from the warm cabin air blown over the  unit. The fan blower should be checked to ensure it rotates  freely. Depending on the system, it should run whenever  the cooling switch is selected and should change speeds as  the selector is rotated to more or less cooling. Sometimes  systems low on refrigerant can cause ice on the evaporator,  16-56 Leak Test Visual Inspection