Electrical Circuit - Komatsu 830E Shop Manual

ELECTRICAL CIRCUIT

The air conditioner' s electrical circuit is fed from an
accessory circuit and is fused with a 30-ampere circuit
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 compres-
sor clutch. Once the blower is turned on, fan speeds
may be changed without affecting the thermostat sens-
ing level.
The thermostat reacts to changing temperatures which
cause electrical contacts to open and close. The ther-
mostat has a capillary tube extended into the evapora-
tor 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 con-
tacts in the thermostat close and the refrigeration 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 prede-
termined point. Evaporator temperature is then main-
tained 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 capillary
tube is attached to the bellows inside of the thermostat.
Expansion of the gases inside the capillary tube exerts
pressure on the bellows, which in turn closes the con-
tacts at a predetermined temperature.
M9-6
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 indicated
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 armature is
mounted on the compressor body.
When no current is fed to the field, there is no magnetic
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 com-
plete 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 compres-
sor is stopped until current is again applied to the field.
In addition, safety switches in the compressor clutch
electrical circuit control clutch operation, disengaging
the clutch if system pressures are abnormal.
Air Conditioning System
for HFC 134a Refrigerant
05/02 M09010