AIR TRACTOR AT-502A, Maintenance Section

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Maintenance Page 32 Air Tractor, Inc.
March 14, 2018 AT-502A/502B/504
3. Application Specifications
A. Oil Flow Theory
•
Compressor lubrication occurs as the oil which circulates with the refrigerant passes
through the compressor crankcase during operation. The Sanden SD series compressor
achieves optimal durability and cooling performance when oil circulates through the
system at a ratio of 3.3% to 8% oil to refrigerant. Excess oil can act as an insulator
limiting heat transfer in the evaporator and condenser, while too little oil can negatively
affect durability.
•
Oil will collect in low pressure cool components (evaporator, accumulator and suction
hose) of the refrigerant loop. For example a long suction hose which sags can collect
several ounces thus reducing overall oil circulation ratio.
B. Oil Charging
a) For a new compressor to be used in this
type of system, subtract the delivered oil
amount from the desired total oil charge to
determine how much oil should be added
to the compressor and system. (For total
system required oil amount, see section
2C, System Requirements above).
b) Remove the oil filler plug and charge the
compressor with the amount of additional oil determined in step a). Use only new oil of the
correct type as shown on the compressor label. If calculated amount is greater than 300cc
(10oz) oil can be added to other system components.
c) Re-install oil plug. Seat and O-ring must be clean and not damaged. Torque to 11-
18 ft•lb
(15-
25 N•m, 150-200 kgf•cm).
4. Diagnosis Confirmation of Compressor Failure
•
The compressor is the most expensive component in the air conditioning system loop.
Steps A through D should be used to determine if the compressor is functioning correctly
or not and prevent removal of a good compressor.
A. Compressor Rotation Test
•
Most internal compressor failures can be
quickly identified by performing a shaft
rotation test. Normal rotation of the
compressor shaft should be smooth
without catching or binding.
•
Compressors which bind or hang during
the shaft rotation test have an internal
part which is broken or contamination
preventing compressor operation. This
compressor should be removed and
replaced with a new unit.