Basic Control - Daikin LRYEQ16AY1 Service Manual

SiBE811001EB

9. Basic Control

9.1 Mounting of Feeler Bulb
9.1.1 Functions of Thermostatic Expansion Valve
1. Functions of thermostatic expansion valve
2. Operation principle of thermostatic expansion valve
CONVENI-PACK
The thermostatic expansion valve reduces the
pressure of high pressure liquid refrigerant from
the condenser to turn it to low pressure liquid
refrigerant (mixed with a small amount of vapor),
thus feeding this refrigerant to the
evaporator.
Internal pressure of
Main unit of
expansion valve
Spring
P
3
pressure
High pressure
liquid refrigerant
Refrigerant inlet
Condenser
P
1
Diaphragm
P
2
Spring
Evaporating
P
3
pressure
pressure
To evaporator
Refrigerant inlet
The feeler bulb and the upper part of diaphragm on
the main unit of expansion valve is connected and
sealed with the capillary tube.
Capillary tube
feeler bulb
P
1
Diaphragm
P
2
Low pressure liquid refrigerant
Evaporating
pressure
To evaporator
Evaporator
The feeler bulb part is charged with the same
refrigerant as that used for the refrigerating
unit, in general.
The feeler bulb is mounted in the evaporator
outlet piping, thus sensing the evaporator outlet
temperature and exerting a force to open the
expansion valve.
This expansion valve introduces the evaporating
pressure (P ) to the lower part of the diaphragm as a
2
valve closing force as opposed to the valve opening
force (P ) exerted on the upper part of the diaphragm.
1
Furthermore, this valve incorporates a spring, which
exerts the valve closing force (P
If the upper and lower forces of the diaphragm keep
equilibrium,
P = P + P
1 2 3
P : Charged fluid pressure (Upper part of diaphragm +
1
Inside of feeler bulb)
As the temperature becomes higher, the valve
opening force becomes larger.
P : In the case of external equalizer pipe
2
·················· Evaporator outlet pressure
In the case of internal equalizer pipe
········· Expansion valve outlet pressure
As the pressure becomes higher, the valve closing
force becomes larger.
P : Spring force (superheated degree setting spring)
3
Constant
Troubleshooting
Connect the external
equalizer pipe on the
downstream side of feeler
bulb of the suction pipe.
External equalizer pipe
Feeler bulb
).
3
318