Komatsu 830E-AC Shop Manual page 938

ELECTRICAL CIRCUIT
The air conditioner's electrical circuit is fed from an
accessory circuit and is fused with a 30-ampere cir-
cuit breaker.
The blower control is a switch which provides a
range of blower speeds from fast to slow. When the
blower switch is turned on, current is available at the
compressor clutch. Once the blower is turned on, fan
speeds may be changed without affecting the ther-
mostat sensing level.
The thermostat reacts to changing temperatures
which cause electrical contacts to open and close.
The thermostat has a capillary tube extended into the
evaporator coil to sense temperature.
When the contacts are closed, current flows to the
clutch field and energizes the clutch, causing the
swash plate inside the compressor to turn which
starts the refrigeration cycle. When the temperature
of the evaporator coil drops to a predetermined point,
the contacts open and the clutch disengages.
When the clutch is disengaged, the blower remains
at the set speed. After the evaporator temperature
rises about twelve degrees above the cutout point,
the contacts in the thermostat close and the refriger-
ation cycle resumes.
Thermostat
An electromagnetic clutch is used on the compressor
to provide a means of constant temperature control
of the cab. The clutch is controlled by a thermostat in
the evaporator which is set initially by the driver to a
predetermined point. Evaporator temperature is then
maintained by the cycling action of the clutch.
The thermostat is simply a thermal device which con-
trols an electrical switch. When warm, the switch is
closed; when cold, it is open. Most thermostats have
a positive OFF position as a means to turn the clutch
off regardless of temperature.
The bellows type thermostat has a capillary tube con-
nected to it which is filled with refrigerant. The capil-
lary tube is attached to the bellows inside of the
thermostat. Expansion of the gases inside the capil-
lary tube exerts pressure on the bellows, which in
turn closes the contacts at a predetermined tempera-
ture.
N4-12
Compressor Clutch
An electromagnetic clutch is used in conjunction with
the thermostat to disengage the compressor when it
is not needed, such as when a defrost cycle is indi-
cated in the evaporator, or when the system or
blower is turned off.
The stationary field clutch is the most desirable type
since it has fewer parts to wear. The field is mounted
to the compressor by mechanical means depending
on the type field and compressor. The rotor is held on
the armature by a bearing and snap rings. The arma-
ture is mounted on the compressor body.
When no current is fed to the field, there is no mag-
netic force applied to the clutch and the rotor is free
to rotate on the armature, which remains stationary
on the crankshaft.
When the thermostat or switch is closed, current is
fed to the field. This sets up a magnetic force
between the field and armature, pulling it into the
rotor. When the armature becomes engaged with the
rotor, the complete unit rotates while the field
remains stationary. This causes the compressor
crankshaft to turn, starting the refrigeration cycle.
When the switch or thermostat is opened, current is
cut off. The armature snaps back out and stops while
the rotor continues to turn. Pumping action of the
compressor is stopped until current is again applied
to the field. In addition, safety switches in the com-
pressor clutch electrical circuit control clutch opera-
tion, disengaging the clutch if system pressures are
abnormal.
Operator Comfort 10/06 N04031