EVAPORATOR COIL
FRONT
DESCRIPTION
The evaporator coil is located in the heater-A/C
housing, under the instrument panel. The evaporator
coil is positioned in the heater-A/C housing so that
all air that enters the housing must pass over the
fins of the evaporator before it is distributed through
the system ducts and outlets. However, air passing
over the evaporator coil fins will only be conditioned
when the compressor is engaged and circulating
refrigerant through the evaporator coil tubes.
OPERATION
Refrigerant enters the evaporator from the expan-
sion valve as a low-temperature, low-pressure mix-
ture of liquid and gas. As air flows over the fins of
the evaporator, the humidity in the air condenses on
the fins, and the heat from the air is absorbed by the
refrigerant. Heat absorption causes the refrigerant to
boil and vaporize. The refrigerant becomes a low-
pressure gas when it leaves the evaporator.
The evaporator coil cannot be repaired and, if
faulty or damaged, it must be replaced.
REAR
DESCRIPTION
The rear evaporator coil is located in the rear over-
head A/C unit housing, above the headliner. The
evaporator coil is positioned in the overhead A/C unit
housing so that all air that enters the housing must
pass over the fins of the evaporator before it is dis-
tributed through the system outlets. However, air
passing over the evaporator coil fins will only be con-
ditioned when the compressor is engaged and circu-
lating refrigerant through the evaporator coil tubes.
OPERATION
Refrigerant enters the evaporator from the rear
expansion valve as a low-temperature, low-pressure
mixture of liquid and gas. As air flows over the fins
of the evaporator, the humidity in the air condenses
on the fins, and the heat from the air is absorbed by
the refrigerant. Heat absorption causes the refriger-
ant to boil and vaporize. The refrigerant becomes a
low-pressure gas when it leaves the evaporator.
The rear evaporator coil cannot be repaired and, if
faulty or damaged, the rear evaporator coil must be
replaced.
EXPANSION VALVE
FRONT
DESCRIPTION
The front “H” valve-type thermal expansion valve
(TXV) is located at the dash panel between the liquid
and suction lines, and the evaporator coil. High-pres-
sure, high temperature liquid refrigerant from the
liquid line passes through the expansion valve ori-
fice, converting it into a low-pressure, low-tempera-
ture mixture of liquid and gas before it enters the
evaporator coil.
OPERATION
A sensor in the expansion valve control head mon-
itors the temperature and pressure of the refrigerant
leaving the evaporator coil through the suction line,
and adjusts the orifice size at the liquid line to let
the proper amount of refrigerant into the evaporator
coil to meet the vehicle cooling requirements. Con-
trolling the refrigerant flow through the evaporator
ensures that none of the refrigerant leaving the evap-
orator is still in a liquid state, which could damage
the compressor.
The expansion valve is a factory calibrated unit
and cannot be adjusted or repaired. If faulty or dam-
aged, the expansion valve must be replaced.
REAR
DESCRIPTION
Vehicles equipped with the optional rear overhead
A/C unit have an H-type thermal expansion valve
(TXV) located underneath the passenger side of the
vehicle floor panel, next to the sill. It performs the
same function as the front expansion valve, to moni-
tor refrigerant temperature and pressure at the con-
trol head and meter the refrigerant entering the
evaporator to meet the vehicle cooling requirements.
OPERATION
The rear expansion valve is a factory calibrated
unit and cannot be adjusted or repaired. If faulty or
damaged, the rear expansion valve unit must be
replaced.
FILTER-DRIER
DESCRIPTION
The filter-drier is mounted on the right front
wheelhouse front extension in the engine compart-
ment, in the liquid line between the condenser outlet
and the evaporator inlet. Refrigerant enters the fil-
ter-drier as a high-pressure, high-temperature liquid.
24 - 6 HEATING AND AIR CONDITIONING DN
DESCRIPTION AND OPERATION (Continued)
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