Case 580SR Service Manual page 799

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PERFORMANCE TEST EXAMPLE 8
7
6
5
1. High side low
2. High side hand valve closed
3. High side hose connected to high side service
connector
4. Not used
PROBLEM
Insufficient cooling.
CAUSE
Improper operation of thermostatic expansion valve
(stuck open).
CONDITIONS*
Low side pressure too low (zero or vacuum). Gauge
should read 1-2 bar.
High side pressure low. Gauge should read 13.3-
14.8 bar.
Evaporator air cool, but not sufficiently cold.
Evaporator inlet pipe surface shows considerable
moisture or frost.
Low pressure switch cutting out.
CORRECTIVE PROCEDURES
1. Place finger on expansion valve to evaporator
tube. If too cold to touch, proceed as follows:
Operate the system at maximum cooling.
SECTION 50 - CAB HEATING AND AIR CONDITIONING
Performance Test Example 8
4
5. Low side hose connected to low side service
connector
6. Low side hand valve closed
7. Low side low
Check the low side gauge. The pressure should
lower slowly.
2. If the procedure outlined in Step 1 shows that
the expansion valve is defective, proceed as fol-
lows:
Discharge the system.
Replace the expansion valve.
Evacuate the system.
Charge the system.
Performance test the system.
DIAGNOSIS
Expansion valve is not permitting a sufficient flow of
refrigerant. May be caused by valve stuck in restrict-
ed or closed position.
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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