Refrigeration Systems

Refrigeration Systems: 

Refrigeration packs and associated components should be checked for security of mountings, security of pipe line connections between components, and level of refrigerant. If the level is low the system should be checked for leaks and, after rectification, recharged with the refrigerant specified for the system taking care that all precautions are observed.

Temperature Control Systems

(a)       All components should be inspected for security of attachment and electrical connection, signs of damage, deterioration of electrical cables etc.

(b)       The operation of individual components should be checked during specified ground tests to ensure that they respond correctly whenever different heating and cooling conditions are selected, and also that, in combination, they maintain cabin temperature conditions within a comfortable range. It should be borne in mind that, apart from considerations of comfort, cabin temperature control limits the misting and icing of windscreens and windows and therefore affects the safe operation of aircraft. The operation of components, systems and circuits, designed specifically for emergency operating conditions, must also be checked during ground test procedures. 10.8.3            The test procedures vary and the extent to which a system can be tested may be limited, particularly in relation to ram air methods of cooling. On the other hand, full-range temperature control of a system in some aircraft may be checked on the ground. Reference must therefore always be made to the relevant Aircraft Maintenance Manual and Maintenance Schedule for the procedure to be adopted and precautions to be observed.

Valves

(a)       The maintenance of valves associated with air temperature control is usually confined to; inspection for cleanliness, security of attachment ducting attachments and, where applicable, security of electrical connections, functioning tests and light lubrication specified by the manufacturer of the component.

(b)       Sliding or rotating parts of valve assemblies should be free from scores, damage or excess static friction. The maximum effort required to move a valve should be checked when necessary and should not exceed the figure recommended by the manufacturer. However some electro-mechanically operated valves are not designed to operate without the application of an electrical supply. Therefore reference should be made to the specific Maintenance Manual for test instructions, before manual operation.

(c)       Lubricants should be of the type specified for the component and should be applied sparingly taking care to prevent oil entering air supply ducts.

(d)       Valve seats and valves faces should be kept free of dust or traces of lubricant.

(e)       Checks on the operation of valves should normally be carried out during ground testing of temperature control systems since their functions are integrated.

  Distribution Systems

(a)       All ducting and associated air distribution components should be inspected for security and general condition, particular attention being given to joints between duct sections and components.

(b)       Lagging should always be properly secured and free from oil, hydraulic fluids etc. It should be remembered that duct sections in some parts of a system often become heated to a degree sufficient to make oil-soaked lagging flammable.

(c)       When specified, ducts should be proof-tested at the pressure recommended by the manufacturer; normally a workshop function. Pressure tests are however, more often made with the object of detecting leaks, in which case the test pressure is not critical provided it does not exceed a value which might damage the duct.

(d)       It is usually more convenient to test a complete distribution system by dividing it into sections and applying a recommended pressure separately and in sequence. The sections should be selected so that all critical joints are subjected to the test pressure; advantage being taken of shut-off valves, non-return valves, etc., where these provide convenient boundaries between sections.

(e)       Leaks can be detected by sound or feel, although these are sometimes revealed by discolouration and holes blown in the lagging. If there is difficulty in locating leaks, the soap and water method can be used.

NOTE: Because of the high operating temperatures and pressures involved, it is recommended that care should be taken when carrying out a physical check for air leaks.