COMPONENTS AIR CONDITIONING Expansion Valves

 

 COMPONENTS AIR CONDITIONING Expansion Valves

 

 

Thermal Expansion Valves

Refrigerant flow to the evaporator must becontrolled to obtain maximum cooling,

while ensuring that complete evaporation  .of the liquid refrigerant takes place. This is  

 accomplished by the thermal expansion ,

valve (TXV).

Pressures in control

As shown in the illustration, the TXV

controls the refrigerant flow by using a

system of opposing pressures which will

call:

F1 - Temperature sensing capillary tube

Sealed tube filled with refrigerant. This

refrigerant is also filled above the

diaphragm (7). The capillary tube sensing

bulb (3) is attached to the evaporator

outlet tube surface.

F2 - Pressure compensation tube

This is a hollow tube connected to the

evaporator outlet tube and senses the

pressure of the R134a refrigerant leaving

the evaporator coil. (Other TX valves may

not use this tube as pressure is provided

internally within the valve).

F3 - Pressure spring

This spring (6) is located under the ball

valve (5).

 

Operation

Open

When the evaporator outlet tube

temperature increases, the refrigerant (3)

in the capillary tube expands, forcing the

diaphragm (7) downwards and thus

pushing pin (A) also downwards causing

the ball valve (5) to move away from the

metering orifice (4), allowing more R134a

to enter the evaporator inlet side.

Closed

As the evaporator outlet tube becomes

cooler, the refrigerant in the capillary tube

(3) contracts. Forces F2 and F3 cause the

diaphragm (7) and pin (A) to move upward

allowing the ball valve to move towards the

metering orifice (4), restricting the R134a

flow. The outlet tube gets warmer and the

process starts over.

 

 kandi younes

Components Automotive Air Conditioning evaporator

 Components Automotive Air Conditioning evaporator  

 

 

Serpentine evaporator

 

R134a enters the evaporator coil as a cold

low-pressure liquid. As this liquid passes

through the evaporator coil, heat moves from

the warm air blowing across the evaporator

fins into cooler refrigerant. This air that has

now been cooled is then ducted into the

cabin via the blower motor.

When there is enough heat to cause a

change of state, a large amount of the heat

moves from the air to the refrigerant. This

causes the refrigerant to change from a lowpressure

cold liquid into a cold vapor. (Latent

heat of evaporation).

As the warmer air blows across the

evaporator fins, moisture contained in that air

(humidity) will condense on the cooler

evaporator fins. Condensed moisture then

runs off through the drain tubes located at the

underside of the evaporator case.

 

Same design as the serpentine

condenser but approximately five times

 

 

Plate & Fin Laminated Evaporators

Similar operation to the parallel flow condenser were the refrigerant has a multi flow pass

creating a large surface area.

Plate & Fin Laminated Evaporator 

( Recommended for R134a)

 

 

R134a - R12 Comparison

Most manufacturers prefer to use the plate and fin design for R134a because of 20%

performance increase over the serpentine design.

 by kandi younes