Chrysler DODGE D150 1993 Service Manual page 1439

24 - 2 HEATING AND AIR CONDITIONING •
housing is expelled through the molded rubber drain
tube into the engine compartment. The tube must be
kept open to prevent condensation from collecting in
the bottom of the housing.
The squeezed rubber flap at the drain tube tip is
designed to keep engine compartment air from enter­
ing into the system yet allow condensation to drain.
If the tip is not properly formed or has been dam­
aged, the system will not drain properly. Therefore,
if the tube is damaged, it should be replaced.
• SERVICE VALVES—The service valves at the
compressor suction line and discharge tube are used
to test and service the refrigerant system. A special
adapter (Tool C-4803) is required for performance
testing.
OPERATION
The compressor increases the pressure and temper­
ature of the refrigerant. The heated refrigerant vapor
is then pumped into the condenser where it cools by
giving off heat to air passing over the condenser fins.
As the refrigerant cools in the condenser, it con­
denses into a liquid. Still under high pressure, the
liquid refrigerant passes into the receiver. The re­
ceiver acts as a reservoir to furnish refrigerant to the
expansion (H) valve at all times. From the receiver,
the high pressure liquid refrigerant passes to the ex­
pansion (H) valve. The expansion (H) valve meters
refrigerant into the evaporator where a low pressure
is maintained by the suction side of the compressor.
As it enters the evaporator, the refrigerant immedi­
ately begins to boil by absorbing heat from the air
passing over the evaporator core. Having given up its
heat to boil the refrigerant, the air is cooled and
passes into the passenger compartment of the vehi­
cle. From the evaporator the vaporized refrigerant is
drawn back to the compressor to repeat the cycle.
RADIATOR CAP
Air conditioned vehicles must be equipped with a
radiator cap having a holding pressure of 98-122
kPag (14-18 psig). Replace the radiator cap t h a t does
not test within this specification.
CONDENSER
Inspect the condenser for obstruction or foreign
matter. Clean if present.
Any obstruction to the free flow of air across the
condenser will decrease heat dissipation from the
condenser. This will in t u r n decrease the efficiency of
the condenser and decrease the evaporator's effi­
ciency. These conditions result in increasing the dis­
charge pressure and horsepower load on the engine.
The use of a bug screen is not recommended, it also
will decrease the free flow of air.
Inspect the condenser for bent or damaged fins.
The bent fins on the condenser deflect air flow and
decrease the condenser area.
BUG SCREENS
Bug screens should NOT be installed on vehicles
equipped with air conditioning. A bug screen in­
stalled in front of the condenser will reduce air flow
and air conditioner performance. Under severe heat
conditions a bug screen may cause the engine to
over-heat.
RESISTOR BLOCK
The blower motor switch and resistor block, con­
trols the speed of the blower motor. The resistor
block consists of 3 helical-wound wire resistors, con­
nected to terminals which are mechanically attached
to a phenolic board. This assembly is bolted to the
plenum.
The blower switch controls the blower motor speed
by selectively connecting in series one, two, three or
none of the resistors to the blower motor.