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TEST CONDITIONS USED TO DETERMINE SYSTEM OPERATION
(THESE TEST CONDITIONS WILL SIMULATE THE AFFECT OF DRIVING THE VEHICLE AND
GIVE THE TECHNICIAN THE THREE CRITICAL READINGS THAT THEY WILL NEED TO
DIAGNOSE ANY POTENTIAL PROBLEMS).
B. CONNECT GAUGES OR SERVICE EQUIPMENT TO HIGH/LOW
CHARGING PORTS.
C. PLACE BLOWER FAN SWITCH ON MEDIUM.
D. CLOSE ALL DOORS AND WINDOWS ON VEHICLE.
E. PLACE SHOP FAN IN FRONT OF CONDENSER.
F. RUN ENGINE IDLE UP TO 1500 RPM.
ACCEPTABLE OPERATING PRESSURE RANGES (R134A TYPE)
1. HIGH-SIDE PRESSURES ( 160-250 PSI ) *Note- general rule of thumb is
two times the ambient (daytime) temperature, plus 15-20%.
2. LOW-SIDE PRESSURES ( 06-22 PSI in a steady state).
CHARGE AS FOLLOWS: R134A = 24 OZ.
NO ADDITIONAL OIL IS NECESSARY IN OUR NEW COMPRESSORS.
TYPICAL PROBLEMS ENCOUNTERED IN CHARGING SYSTEMS
NOISY COMPRESSOR. A noisy compressor is generally caused by charging a
compressor with liquid or overcharging
A. If the system is overcharged both gauges will read abnormally high readings.
This is causing a feedback pressure on the compressor causing it to rattle or
shake from the increased cylinder head pressures. System must be evacuated
and re-charged to exact weight specifications.
B. Heater control valve installation - Installing the heater control valve in the
incorrect hose. Usually when this occurs the system will cool at idle then start
to warm up when raising the RPM's of the motor. THE HEATER CONTROL IS
A DIRECTIONAL VALVE; MAKE SURE THE WATER FLOW IS WITH THE
DIRECTION OF THE ARROW. As the engine heats up that water transfers the
heat to the coil, thus overpowering the a/c coil. A leaking or faulty valve will
TROUBLESHOOTING GUIDE
C. Evaporator freezing - Freezing can occur both externally and internally on
D. Internal freeze up occurs when there is too much moisture inside the
E. Inadequate airflow to condenser - The condenser works best in front of
F. Incorrect or inadequate condenser capacity - Incorrect condenser
G. Expansion valve failure - An expansion valve failure is generally caused by
have a more pronounced affect on the unit's cooling ability. Installing the valve
improperly (such as having the flow reversed) will also allow water to flow
through, thus inhibiting cooling. Check for heat transfer by disconnecting
hoses from the system completely. By running down the road with the hoses
looped backed through the motor, you eliminate the possibility of heat transfer
to the unit.
an evaporator core. External freeze up occurs when the coil cannot effectively
displace the condensation on the outside fins and the water forms ice (the
evaporator core resembles a block of solid ice), it restricts the flow of air that
can pass through it, which gives the illusion of the air not functioning. The
common cause of external freezing is the setting of the thermostat and the
presence of high humidity in the passenger compartment. All door and
window seals should be checked in the event of constant freeze-up. A
thermostat is provided with all units to control the cycling of the compressor.
system. The symptoms of internal freeze up often surface after extended
highway driving. The volume of air stays constant, but the temperature of the
air gradually rises. When this freezing occurs the low side pressure will drop,
eventually going into a vacuum. At this point, the system should be checked by
a professional who will evacuate the system and the drier will have to be
changed.
the radiator with a large supply of fresh air. Abnormally high pressures will
result from improper airflow. Check the airflow requirements by placing a large
capacity fan in front of the condenser and running cool water over the surface.
If the pressures drop significantly, this will indicate the need for better airflow.
capacity will cause abnormally high head pressures. A quick test that can be
performed is to run cool water over the condenser while the system is
operating, if the pressures decrease significantly, it is likely a airflow or
capacity problem.
dirt or debris entering the system during assembly. If an expansion valve fails
it will be indicated by abnormal gauge readings. A valve that is blocked will be
indicated by high side that is unusually high, while the low side will be
www.classicautoair.com • 866.435.7801
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