Suzuki XL7 2007 Service Manual page 1820

7A-6 Heating, Ventilation and Air Conditioning:
Engine Coolant
Engine coolant is the key element of the heating system.
The thermostat controls engine operating coolant
temperature. The thermostat also creates a restriction
for the cooling system that promotes a positive coolant
flow and helps prevent cavitation. Coolant enters the
heater core through the inlet heater hose, in a
pressurized state.
The heater core is located inside the HVAC module. The
heat of the coolant flowing through the heater core is
absorbed by the ambient air drawn through the HVAC
module. Heated air is distributed to the passenger
compartment, through the HVAC module, for passenger
comfort.
The amount of heat delivered to the passenger
compartment is controlled by opening or closing the
HVAC module air temperature door. The coolant exits
the heater core through the return heater hose and
recirculated back through the engine cooling system.
A/C Cycle
Refrigerant is the key element in an air conditioning
system. R-134a is presently the only EPA approved
refrigerant for automotive use. R-134a is a very low
temperature gas that can transfer the undesirable heat
and moisture from the passenger compartment to the
outside air.
The A/C compressor is belt driven and operates when
the magnetic clutch is engaged. The compressor builds
pressure on the vapor refrigerant, which adds heat to the
refrigerant. The refrigerant is discharged from the
compressor, through the discharge hose, and forced to
flow to the condenser and then through the balance of
the A/C system. The A/C system is mechanically
protected with the use of a high pressure relief valve. If
the high pressure switch were to fail or if the refrigerant
system becomes restricted, and the refrigerant pressure
continues to rise, the high pressure relief valve will pop
open and release refrigerant from the system.
HVAC Schematics
Schematic and Routing Diagram
Compressed refrigerant enters the condenser in a high
temperature, high pressure vapor state. As the
refrigerant flows through the condenser, the heat of the
refrigerant is transferred to the ambient air passing
through the condenser. Cooling the refrigerant causes
the refrigerant to condense and change from a vapor to
a liquid state.
The condenser is located in front of the radiator for
maximum heat transfer. The condenser is made of
aluminum tubing and aluminum cooling fins, which
allows rapid heat transfer for the refrigerant. The semi-
cooled liquid refrigerant exits the condenser and flows
through the liquid line, to the thermal expansion valve
(TXV).
The TXV is located at the evaporator inlet and outlet
pipes. The TXV is the dividing point for the high and the
low pressure sides of the A/C system. As the refrigerant
passes through the TXV, the pressure on the refrigerant
is lowered. Due to the pressure differential on the liquid
refrigerant, the refrigerant will begin to boil at the TXV.
The TXV also meters the amount of liquid refrigerant that
can flow into the evaporator.
Refrigerant exiting the TXV flows into the evaporator
core in a low pressure, liquid state. Ambient air is drawn
through the HVAC module and passes through the
evaporator core. Warm and moist aircause the liquid
refrigerant to boil inside of the evaporator core. The
boiling refrigerant absorbs heat from the ambient air and
draws moisture onto the evaporator. The refrigerant exits
the evaporator through the suction line and back to the
compressor, in a vapor state, and completing the A/C
cycle of heat removal. At the compressor, the refrigerant
is compressed again and the cycle of heat removal is
repeated.
The conditioned air is distributed through the HVAC
module for passenger comfort. The heat and moisture
removed from the passenger compartment condense,
and is discharged from the HVAC module as water.