Komatsu 830E, Shop Manual

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M09010 05/02 Air Conditioning System M9-19
for HFC 134a Refrigerant
Receiver-Drier
The receiver-drier can not be serviced or repaired. It
must be replaced whenever the system is opened
for any service. The receiver-drier has a pressure
switch to control the clutch, and should be removed
and installed onto the new unit.
Thermostat
A thermostat can be stuck open or closed due to con-
tact point wear or fusion. The thermostat temperature
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 sys-
tem. Side effects can be compressor damage caused
by oil accumulation (refrigeration oil tends to accumu-
late at the coldest spot inside the system) and lower
than normal suction pressure that can starve the com-
pressor of oil.
Compressor
The compressor can fail due to shaft seal leaks (no
refrigerant in the system), defective valve plates, bear-
ings, or 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.
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
enlarge the slots in the compressor mounting bracket
to achieve proper alignment.
Excessive clutch plate wear is caused by the plate rub-
bing 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
0.023 to 0.057 in. (1.02 ± 0.043 mm). 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.
NOTE: Some compressors may be discarded
because it is suspected that internal components
within the compressor have seized. Ensure that the
compressor clutch is working properly before dis-
carding a compressor for internal seizure. The nor-
mal compressor life span should be about twice as
long as the normal life span of the compressor
clutch.
It is important to note that often times a weak clutch coil
may be mistaken for a seized compressor. When a
coil’s resistance has increased over time and the mag-
netic field weakens, the coil may not be able to pull the
load of the compressor. Failure of the coil to allow the
compressor shaft to be turned, may appear as though
the compressor is locked up.