Kubota B1830, Workshop Manual

Page: 494 / 548

CABIN B1830,B2230,B2530,B3030, WSM
10-M17
When the vapor pressure of the operating system is
stable, Pf = Pe + Ps condition will prevail. At this time the
needle valve opening will be stationary and constant
refrigerant flow will be maintained.
The quantity of the refrigerant vaporizing into the
evaporator tube (6) is controlled by the needle valve (2)
(the clearance between needle valve and the expansion
valve body). When constant refrigerant vaporizes into
the evaporator tube (6) and the temperature in the cabin
increases, the refrigerant in the evaporation tube
evaporates quickly. This causes the super heated
temperature in part
B in the figure. If the cooling load
increases (inlet air temperature of evaporator becomes
high), the refrigerant will vaporize faster and cause the
length of the superheated vapor part
B to become
longer. Thus, the pressure in the heat sensitive tube (7)
rises and increases the needle valve opening, resulting
in larger flow of the refrigerant into the evaporator.
Conversely, if the amount of refrigerant in the evaporator
increases, the length of the superheated vapor part
B will
become shorter. The pressure in the heat sensitizing
tube will drop and decrease the needle valve (2)
opening.
9Y1210003CAM0021US0
(2) Evaporator
The purpose of the evaporator (2) is just opposite to
that of the condenser. The state of refrigerant
immediately after the expansion valve is 100 % liquid. As
soon as the liquid pressure drops, it starts to boil, and in
doing so, absorbs heat. This heat is removed from the air
passing over the cooling fins of the evaporator and
causes the air to cool.
If too much refrigerant is sent into the evaporator, it
will not boil as easily. If the evaporator is filled with liquid
refrigerant, it eliminates a place for the refrigerant to
properly vaporize. This vaporization is necessary in
order to absorb heat. A flooding condition of the
evaporator will allow an excess of liquid refrigerant to
leave the evaporator and may cause serious damage to
the compressor.
If too little refrigerant is sent into the evaporator,
again the evaporator will not cool because the refrigerant
will vaporize, or boil off, long before it passes through the
evaporator.
Refrigerant properly metered into the evaporator
should allow for 100 % liquid just after the expansion
valve, and 100 % gas at the outlet.
9Y1210003CAM0022US0
(1) Diaphragm
(2) Needle Valve
(3) Refrigerant Inlet
(4) Spring
(5) Adjusting Screw
(6) Evaporator Tube
(7) Heat Sensitive Tube
(8) Capillary Tube A: Saturated Vapor Part
B: Superheated Vapor Part
Pf: Gas pressure in sensitizing
tube
Ps: Spring pressure
Pe: Vapor pressure in
evaporator
(1) Expansion Valve
(2) Evaporator
(3) Heater Core (4) Fin
(5) Tube
KiSC issued 05, 2012 A