40 SECTION 50 - CAB HEATING AND AIR CONDITIONING
PERFORMANCE TEST EXAMPLE 9
Performance Test Example 9
1. High side low
2. High side hand valve closed
3. High side hose connected to high side service
connector
4. Not used
5. Low side hose connected to low side service
connector
6. Low side hand valve closed
7. Low side low
PROBLEM
Little or no cooling.
CAUSE
Restriction in high side of system.
CONDITIONS*
Low side pressure too low. Gauge should read 1-2
bar.
High side pressure too low. Gauge should read
13.3-14.8 bar.
NOTE: a normal or high reading of the high side
pressure gauge under these conditions indicates
the system is overcharged or the condenser or re-
ceiver/dryer is too small.
Evaporator only slightly cool.
Liquid line and receiver/dryer are cool to touch and
show frost or considerable moisture.
CORRECTIVE PROCEDURES
1. Check for sticking expansion valve as follows:
Operate the system at maximum cooling.
Check the low side gauge. The pressure should
lower slowly.
2. If the test indicates that the expansion valve is
defective, proceed as follows:
Discharge and recover the refrigerant from the
system.
Replace the expansion valve.
Evacuate the system.
Charge the system.
Performance test the system.
DIAGNOSIS
Thermostatic expansion valve is allowing too much
refrigerant to flow through the evaporator coils.
Valve may be stuck open.
NOTE: * test procedure based upon ambient tem-
perature of 35 °C.
For proper high side gauge reading for other ambi-
ent temperatures, refer to the pressure temperature
chart.
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F28706
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