MCi Crusader II 1989 Maintenance Manual page 492

Date
1-1-89
Page. __
1_s_-2_2 _ _
MC-9 MAINTENANCE MANUAL
A/C SYSTEM TROUBLESHOOTING (CONT'D)
SUPERHEAT TOO HIGH
REDUCED AIR FLOW:
(A) DIRTY OR CLOGGED AIR FILTER
(B) C/H BLOWER INOPERATIVE
(C) PLUGGED RETURN AIR DUCTS
Dirty or iced evaporator coil.
TOO FREQUENT STARTING ANO STOPPING
ON LOW PRESSURE CONTROL SWITCH
Lack of refrigerant.
COMPRESSOR INTERMITTENTLY STARTS
ANO STOPS
Intermittent contact in electrical control circuit.
Compressor valves not in operating position.
FREQUENT STARTING AND STOPPING
Low pressure switch controller differential set
too close.
FREQUENT STARTING AND STOPPING
High pressure switch controls differential too
close.
AIR CONDITIONING COMPRESSOR
The Model 05G compressor is of the open reciprocating
type, that is, of positive displacement. Compressor wear is
minimized by splash lubrication and force feed lubrication.
which is accomplished by a low-speed oil pump driven
directly from the end of the compressor crankshaft. A
mechanical seal prevents refrigerant leakage where the
rotating shaft passes through the crankcase.
The compressor is equipped with flanges for connecting
suction and discharge service valves. Sight glasses, in-
stalled on both sides of the crankcase, provide a means for
checking oil level in the compressor crankcase. A drain
plug facilitates draining of oil from the crankcase and an oil
fill plug enables addition of oil when necessary. A bottom
plate provides access through the bottom of the crankcase
for maintenance.
The compressor uses reed type suction and discharge
valves made of highest quality steel for long life. The valves
operate against hardened integral seats in the valve.
The pistons move in a straight line, but alternately in
divergent directions. The downstroke of the piston admits
refrigerant gas through the suction valve, and then com-
presses this gas on the upstroke, thereby raising its
temperature and pressure. The compressed gas is pre-
vented from re-entering the cylinder on its next downstroke
by the compressor discharge valve.
The 05G compressor uses pressure-operated unloaders.
These unloaders are~ of the snap-action, cylinder head
bypass type, using a piston-type control valve to control
discharge gas flow (figure 16-22).
The pressure-operated unloaders are controlled by suc-
tion pressure and actuated by discharge pressure. Each
1. Reset superheat adjustment.
2. Check for clogged external equalizer line, or dehydrator.
1. Clean air filter screen.
2. Check return ducts for obstructions.
3. Check blower motor.
1 . Check for leaks.
2. Recharge.
1. Check control circuit components.
2. Check compressor valve operation.
Check and adjust.
Replace switch assembly.
VALVE BODY
ADJUSTING SCREW
ir====:::::t------
BYPASS PISTON RING
~r------
BYPASS PISTON
----
Figure 16-22: Compressor Capacity Control Loader
unloader valve controls two cylinders. On startup. con-
trolled cylinders do not loadup until differential between
suction and discharge pressure is 10 psi (69 kPa).
During loaded operation, when suction pressure is above
the valve control point, the poppet valve will close. Dis-
charge gas bleeds into the valve chamber. the pressure
closes the bypass piston, and the cylinder bank loads up.
Discharge gas pressure forces the check valve open, per-
mitting gas to enter the discharge manifold.·
During unloaded operation. when suction pressure drops
below the valve control point, the poppet valve will open.