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 TM 55-1905-219-14-8
4-28. AIR CONDITIONING SYSTEM - MAINTENANCE INSTRUCTIONS (Continued).
h. Capacity Control System.
(1)
Description of Capacity Control.
(a) The compressor is equipped with a capacity control system operated by oil pressure from the
compressor lubrication system. The capacity control system unloads cylinders (that is, cuts cylinders out of
operation) in response to decreases in the refrigeration load imposed on the compressor. Unloading of a
controlled cylinder is accomplished by holding the cylinder suction valve off its seat (open) so that no gas can
be compressed. The suction valve lifting arrangements for the compressor is shown below.
Suction Valve Lifting Arrangement
(b) The capacity control system operates in steps, each step on a given compressor unloading one
or more of the controlled cylinders as shown in the table below.
Capacity Control System Steps of Unloading
Compressor
No. of Controlled
Step 1
Step 2
Model
Cylinders
No. of Unloaded Cylinders
(Compressor Capacity After Unloading
5F30
2 of 3
1
2
(66-2/3%)
(33-1/3%)
4-850
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