TIAGO

HVAC

iii) EVAPORATOR COIL AND TXV

(THERMAL

EXPANSION VALVE)

EVAPORATOR COIL

It is a heat exchanger cum dehumidifier which ab-

sorbs heat and moisture of the air passing through it

to give cold dehumidified air. As the refrigerant ab-

sorbs the heat it changes its state from liquid to

vapour. A thermistor (

temperature sensor)

is used to

measure the temperature of the air passing over the

evaporator in order to avoid freezing.

TXV (

THERMAL EXPANSION VALVE

)

The TXV used is block type valve. It consists of a

two passages one for refrigerant flowing into the

evaporator and the other for refrigerant coming out of

evaporator and into the compressor. A temperature

sensing element is placed in the outlet passage. This

sensing element is filled with a fluid which expands

and contracts when there is rise or fall in the temper-

ature. When the temperature of the refrigerant

flowing out of the evaporator rises it causes the ex-

pansion of the refrigerant in the sensing element

which in turn pushes the pin, such that the ball valve

blocking the orifice opens to allow more refrigerant

into the evaporator. The pressure spring provided

below the ball tends to close the ball valve and

hence this pressure has to be overcome in order to

open the valve.

There is a passage in the block valve where refriger-

ant flowing out can build pressure under a

diaphragm on which the sensing element is mounted

causing the diaphragm to move up; this provides the

needed pressure correction while regulating the re-

frigerant into the evaporator.

iv) HEATER COIL

A heater coil is

a radiator-

like device used in heating

the cabin of

a vehicle.

t coolant

from the vehicle's

engine

is passed through a winding tube of the core,

a heat exchanger between coolant and cabin air.

Fins attached to the core tubes serve to increase

surface for heat transfer to air that is forced past

them, by a fan, thereby heating the passenger com-

partment.