Cold Air Units

Cold Air Units

(a)       When installing cold air units care is necessary to exclude dirt and oil from the air ducts and casings. Dirt and other foreign matter may damage the rotating parts and oil may introduce unpleasant or flammable vapours into the cabin air supply. Duct attachment flanges, unit mounting flanges, and casings, should be examined for signs of burns, cracks, distortion or other damage.

(b)       Units with integral wet sump lubrication should be primed with oil to the approved specification to ensure that all bearing surfaces have been lubricated. Reference should be made to the Maintenance Manuals of relevant units for details of the lubricants required. The unit should be supported on a bench in the normal operating attitude while the quantity of oil specified for the unit is poured in. To ensure that oil is distributed to the bearings, the rotating assembly of the unit should be spun over by hand at the same time checking that the rotation is free and without noise or vibration (see Note). The unit should then be drained and installed in the aircraft and after securing it to its appropriate mounting, refilled with oil to the level marked on the sump dipstick.

NOTE: In some cold air units, air bearings are used to support the main rotating assembly, which do not allow free rotation from the idle state. Therefore reference should be made to the specific Maintenance Manual for further details.

(c)       The lubricants recommended for Cold Air Units are various and possibly incompatible with each other. Therefore, when priming or servicing these units, care should be taken to ensure that the oil is of the correct type and specification and the containers used are clean and free from contamination of any kind.

(d)       New seals should be fitted between the air distribution ducts and attachment flanges on the cold air unit, and when securing the ducts it should be ensured that they fit squarely and are not subjected to undue strain or load. Leak checks on units should be carried out during functional testing of the air conditioning system.