Chevrolet Light Duty Truck 1973 Service Manual page 56

1A-30 HEATER A ND AIR C O N D IT IO N IN G
drilled in the head between the two. The unit number is
stamped on a plate attached to the counterclockwise
rotation head and a decal arrow indicates the direction
of rotation.
Mainshaft
The central mainshaft, driven by the clutch-pulley when
the coil is energized, extends through the front head to
the rear head and oil pump cavity of the compressor.
The shaft revolves in needle roller bearings located in
the front and rear halves of the cylinder assembly. A
3/16" internally drilled passage extends through the
shaft from the rear oil pump cavity to the shaft seal
cavity in the front compressor head. Four .078 inch
holes, drilled at 90° to the main passage, direct oil under
pump pressure to the shaft seal surfaces, thrust bearings
and shaft-cylinder bearings.
Wobble Plate
The wobble plate is an angular shaped member pressed
onto the mainshaft forming the mainshaft and wobble
plate assembly (fig. 35). A woodruff key prevents
movement of the plate around the shaft. Location of the
plate on the shaft is factory set and must not be changed.
The very smooth angular faces of the plate are ground to
be parallel within .0003 inches of each other. The plate
changes the rotating action of the shaft into the
reciprocating driving force for three pistons. The driving
force is applied, through the drive balls and ball seats
(shoe discs) to the midpoint of each of the double end
pistons.
Cylinder Block
The cylinder block consists of a front and a rear half.
Three piston bores are line bored in each half during
production to assure proper alignment and parallelism.
The two halves must be serviced as an assembly to assure
correct relationship of parts.
Pistons
The cast aluminum double end pistons (fig. 35), have
grooves to receive piston rings. Each ring has an oil
scraper groove which should face away from the piston
face. Two oil return passages are drilled from each ring
groove. A notch in the casting web of each piston
identifies the end of the piston which should be
positioned toward the front end of the compressor. A
spherical cavity is located on both inner faces of each
piston to receive the piston drive balls.
Drive Balls
The hardened steel drive balls have a micro-finish. They
are manufactured to a .0001 inch spherical tolerance and
a .6248 - .6250 inch diameter tolerance.
Ball Seats
The bronze ball seats have one flat side, which contacts
the wobble plate, and one concave surface into which the
drive ball fits. Ten seats are provided in .0005 inch
thickness variations including a basic ZERO seat for
simple field gauging operations. Seats are marked with
their size which corresponds to the last three digits of the
piece part number.
Selection from this group must be made to provide .0005
inch to .0010 inch total clearance between the ball seats
and the wobble plate at the tightest place throughout its
360° rotation (fig. 36).
Thrust Bearings
The thrust bearings, sandwiched between two thrust
races (see below) are located between the shoulders of
the wobble plate and the shoulders of both the front and
rear cylinder hubs.
Thrust Races
The steel thrust races are ground to fixed thicknesses. A
total of 14 races in increments of .0005 inch thickness
are available for field service. As in the case of the ball
seats the thrust races will be identified on the part by
their thickness, the number on the race corresponding to
the last three digits of the piece part number. The
FRONT combination of a race, bearing and race is
selected to provide the proper head clearance between
the top of the cylinder and the underside of the suction
and discharge valve plates. The REAR end combination
of bearing and races is selected to obtain .0005 inch low
limit to .0015 inch high limit running clearance between
the hub surfaces of the wobble plate and the front and
rear hubs of the cylinder (fig. 36). This allows .001 inch
tolerance between the high and low limits.
Oil Pump Gears
The oil pump gears are made of sintered iron. The inner,
or driver gear has a "D " shaped hole in the center which
fits over a similar area on the rear of the mainshaft.
Shell
The compressor shell has a mounting flange on the front
end and four threaded studs welded to the outside of the
rear end. The oil sump is formed into the shell and a
baffle plate is welded over the sump on the inside of the
shell.
Heads
Both front and rear heads have an irregular shaped
casting web. These webs provide the necessary seals to
the surfaces of the discharge plates and prevent high
pressure vapor from flowing into the low pressure cavity.
Suction Screen
A fine mesh inlet (or suction) screen is located in the low
pressure cavity of the rear head. Its purpose is to stop
any material which could damage the compressor
mechanism.
Suction Cross-Over Cover
The suction cross-over cover, with its neoprene seal is
pressed into the dove-tail cavity in the front and rear
cylinder castings to form a passage for the low pressure
LIGHT DUTY TRUCK SERVICE MANUAL