SECTION 22: HEATING AND AIR CONDITIONING
18
DOB 2490-2789 | X3-45 Commuter PA1605 Maintenance Manual (Final Version – Rev.2 April 2016)
6. AIR CONDITIONING SYSTEM
The schematic of FIGURE 3 shows the A/C
systems and their components.
The HVAC system is equipped with a 4 cylinder,
4NFCY Bitzer compressor with an air conditioning
capacity of 7½ tons. The receiver tank and filter-
dryer are mounted inside the condenser
compartment.
6.1 A/C
CYCLE
Refrigeration may be defined as "the transfer of
heat from a place where it is not wanted to a
place where it is unobjectionable". Components
required for a closed circuit refrigeration system
are shown in FIGURE 3.
The air conditioning system used on X series
vehicles is of the
"Closed"
type using
"R-134a".
1. The refrigerant flowing to the compressor is
compressed to high pressure and reaches a
temperature higher than the surrounding air.
It is passed through the air-cooled fins and
tubes of the condenser causing the hot,
high pressure gas to be condensed into a
liquid form.
2. The liquid refrigerant flows to the receiver
tank, then passes through a filter-dryer
where moisture, acids and dirt are removed
and then through a moisture indicator which
indicates if any moisture is present in the
system.
3. By its own pressure, the liquid refrigerant
flows through a thermal expansion valve
where the pressure drop causes the
refrigerant to vaporize in a vapor-liquid state
at a low temperature pressure.
4. The cold low pressure refrigerant passes
through the passengers and the driver’s
evaporator coils which absorbs heat from
the air passing over the fins and tubes, and
changes into gas. In this form, the
refrigerant is drawn into the compressor to
repeat the air conditioning cycle.
5. The success of the air conditioning system
depends on retaining the conditioned air
within the vehicle. All windows and intake
vents should be closed. An opening of
approximately 8 in
2
(5162 mm
2
) could easily
neutralize the total capacity of the system.
6. Other causes of inadequate cooling are
dirty coils or filter. Dirt acts as insulation and
is also serves as a restriction to the air flow.
7. The refrigeration load is not constant and
varies. It is also affected by outside
temperature, relative humidity, passenger
load, compressor speed, the number of
stops, etc.
8. The compressor will load or unload
depending on operating conditions.
6.2 REFRIGERANT
The A/C system of this vehicle has been
designed to use R134a refrigerant. Regardless
of the brand, only R-134a must be used in this
system. The chemical name for this refrigerant is
Ethane, 1, 1, 1, 2-Tetrafluoro.
DANGER
Refrigerant in itself is nonflammable, but if it
comes in contact with an open flame, it will
decompose.
6.2.1 Procurement
Refrigerant is shipped and stored in 30 and 100
pound metal cylinders. Approximately 24 lbs are
used in the HVAC system plus an additional 2.0
lbs will be needed for the parcel rack A/C
system.
Refrigerant charge (Approximately)
A/C
system:
24
lbs
Parcel rack A/C system:
2 lbs
Total:
26 lbs
It will be impossible to draw the entire refrigerant
out of the cylinder. However, the use of warm
water or heating blanket when charging the
system will assure the extraction of a maximum
amount of refrigerant from the cylinder.
6.2.2 Precautions in Handling Refrigerant
1. Do not leave refrigerant cylinder uncapped.
2. Do not subject cylinder to high temperatures,
do not weld or steam clean near system or
cylinder.
3. Do not fill cylinder to more than 80% liquid
full to allow for refrigerant expansion.
4. Do not discharge vapor into an area where
a flame is exposed.
5. Do not expose the eyes to liquid refrigerant.
All refrigerant cylinders are shipped with a heavy
metal screw cap. The purpose of the cap is to
protect the valve and safety plug from damage.
