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.
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