Service Manual

627333-A 5-21
HVAC
EVAPORATOR COIL
FIG. 12: Evaporator Operation
Evaporator (1) is located in HVAC unit in front of heater
coil.
Evaporator transfers heat in cab to refrigerant.
Evaporator receives liquid refrigerant, with low pressure
and temperature. Since pressure of liquid refrigerant is
low, temperature of saturation of refrigerant is low. As
temperature of saturation changes, refrigerant changes
from liquid to vapor.
Blower fan exposes evaporator coil to air inside cab.
Heat from air inside cab is absorbed by evaporator
transferring heat to refrigerant, at which time it reaches
temperature of saturation and changes from a liquid to
a vapor. The amount of heat required to reach
temperature of saturation is called latent heat of
vaporization. Vaporized refrigerant leaves evaporator
and carries heat away from cab. Vaporized refrigerant
returns to compressor when refrigerant leaves
evaporator. This process is repeated continuously.
Temperature of evaporator coil is monitored by a
temperature sensor inserted into evaporator coil.
See Systems Operation/Testing and Adjusting,
Temperature Sensors for additional information.
HEATER CORE (CAB)
FIG. 13: Heater core (1) is located in HVAC unit.
Airflow is forced past heater core to gain heat from
engine coolant. Engine coolant is circulated through
heater core. Airflow is created by blower fan in HVAC
unit.
Heater core is constructed of copper and aluminum as
these metals are excellent heat conductors. Heater
core and water valve are connected with a heater hose.
These connections are critical and should be checked
periodically for leaks.
FIG. 12
1
M121103010
FIG. 13
1
M121103010