Komatsu 930E-2, Shop Manual

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Receiver-Drier
The receiver-drier can not be serviced or repaired. It
should be replaced whenever the system is opened for
any service. If the receiver-drier has a pressure switch
to control the clutch, it should be removed and installed
on the new unit.
Thermostat
A thermostat can be stuck open or closed due to
contact point wear or fusion. The thermostat tempera-
ture sensing element (capillary tube) may be broken or
kinked closed and therefore unable to sense evapora-
tor temperature.
When thermostat contact points are stuck open or the
sensing element can not sense temperature in the
evaporator, the clutch will not engage (no AC system
operation). Causes are a loss of charge in the capillary
tube or a kink, burned thermostat contact or just no
contact. When troubleshooting, bypass the thermostat
by hot wiring the clutch coil with a fused lead. If the
clutch engages, replace the thermostat.
Thermostat contact points may be fused (burned)
closed and the clutch will not disengage. Causes are a
faulty switch that could be due to fatigue. The thermo-
stat must be replaced. When the clutch will not disen-
gage you may also note that condensate has frozen on
the evaporator fins and blocked air flow. There will also
be below normal pressure on the low side of the
system. Side effects can be compressor damage
caused by oil accumulation (refrigeration oil tends to
accumulate at the coolest spot inside the system) and
lower than normal suction pressure that can starve the
compressor of oil.
Clutch
Clutch problems include electrical failure in the clutch
coil or lead wire, clutch pulley bearing failure, worn or
warped clutch plate or loss of clutch plate spring tem-
per. Defective clutch assembly parts may be replaced
or the whole assembly replaced. If the clutch shows
obvious signs of excessive heat damage, replace the
whole assembly.
The fast way to check electrical failure in the lead wire
or clutch coil is to hot wire the coil with a fused lead.
This procedure enables you to bypass clutch circuit
control devices.
Clutch pulley bearing failure is indicated by bearing
noise when the AC system is off or the clutch is not
engaged. Premature bearing failure may be caused by
poor alignment of the clutch and clutch drive pulley.
Sometimes it may be necessary to use shims or en-
large the slots in the compressor mounting bracket to
achieve proper alignment.
Excessive clutch plate wear is caused by the plate
rubbing on the clutch pulley when the clutch is not
engaged or the clutch plate slipping when the clutch
coil is energized. A gap that is too small or too large
between the plate and clutch pulley or a loss of clutch
plate spring temper are possible causes. The ideal air
gap between the clutch pulley and the clutch plate is
0.022 to 0.057 in. If the gap is too wide, the magnetic
field created when the clutch coil is energized will not
be strong enough to pull and lock the clutch plate to
the clutch pulley.
Compressor
The compressor can fail due to shaft seal leaks (no
refrigerant in the system), defective valve plates, bear-
ings, other internal parts or problems associated with
high or low pressure, heat or lack of lubrication. Be sure
the compressor is securely mounted and the clutch
pulley is properly aligned with the drive pulley.
Use a mechanic’s stethoscope to listen for noises
inside the compressor.
CHECKING COMPRESSOR OIL LEVEL
Every air conditioning system and compressor de-
pends on refrigeration oil for lubrication and safe op-
eration.
Refrigerant oil is a synthetic oil very susceptible to high
levels of water absorbtion. Always be sure the oil is an
approved type for use in the air conditioner compres-
sor.
Refrigerant oil, under normal circumstances inside the
sealed system, cannot go anywhere, and there is no
need to check the oil at such times. Always keep a cap
on an oil container except when in use. Moisture is
quickly absorbed by the oil.
Whenever a system is opened for service, the com-
pressor oil level should be checked and clean refrig-
eration oil added as required by the manufacturer’s
specifications (usually located on compressor).
M09010 6/97 Air Conditioning System M9-17
for HFC 134a Refrigerant