Komatsu PC88MR-10 Shop Manual page 1338

80 Appendix
Air conditioner unit
Operation
(ALL-K548-044-K-00-A)
Thermoprobe (1a-2) senses the refrigerant temperature after it passes through the evaporator (3).
After the refrigerant passes through evaporator (3), its temperature is transferred to the refrigerant gas (2)
in the diaphragm chamber (hatched area) through the thermoprobe (1a-2).
The pressure of the refrigerant gas (2) sealed in the diaphragm chamber (hatched area) changes in
response to the temperature change of the thermoprobe (1a-2), which therefore changes the force (Fg)
pushing the needle valve (1a).
The opening level of the needle valve (1a) is determined based on the balance between the reaction force
exerted by the spring (1b) in a rightward direction, and the force (Fg) of the refrigerant gas (2) pushing the
needle valve (1a) through the diaphragm (1a-1) in a leftward direction.
The refrigerant flow rate flowing from the receiver drier to evaporator (3) is determined based on the
opening level of needle valve (1a).
When evaporator (3) outlet temperature is high: [When not cooled yet: Condition (A) in the figure]
The pressure of the refrigerant gas (2) in the diaphragm chamber is high and the volume is increased.
The force (Fg) of the refrigerant gas (2) pushing the needle valve (1a) is increased, and the needle valve
(1a) moves leftward.
As a result, the opening level of the needle valve (1a) is increased and the refrigerant flow rate to the
evaporator (3) is increased to improve cooling capacity. (Condition (A) in previous figure)
When evaporator (3) outlet temperature is low: [When cooled already: Condition (B) in the figure]
The pressure of the refrigerant gas (2) in the diaphragm chamber is low and the volume is decreased.
The force (Fg) of the refrigerant gas (2) pushing the needle valve (1a) is reduced, and the needle valve
(1a) is moved rightward by the reaction force of spring (1b).
The opening level of the needle valve (1a) is reduced and the refrigerant flow rate to the evaporator (3) is
reduced to lower the cooling capacity. (Condition (B) in previous figure)
80-14 PC88MR-10