SECTION 22: HEATING AND AIR CONDITIONING
PA1621 Maintenance Manual All Series | Section Revised November 2017
47
5.7.2 Expansion Valve
PROBABLE CAUSE PROBABLE REMEDY
LOW SUCTION PRESSURE-HIGH SUPERHEAT
EXPANSION VALVE LIMITING FLOW:
Gas in liquid line due to pressure drop in the line
or insufficient refrigerant charge.
Locate cause of line flash and correct by use of
any of the following methods. Add R-134a.
Replace filter-dryer.
Superheat adjustment too high. Adjust superheat as outlined under "Superheat
Adjustment".
Power assembly failure or partial loss of charge. Replace expansion valve.
Air filter screen clogged. Clean or replace air filter screen.
Plugged / kinked / chaffed lines. Clean, repair or replace lines.
LOW SUCTION PRESSURE-LOW SUPERHEAT
Uneven or inadequate evaporator loading due to
poor air distribution or liquid flow.
Balance evaporator load distribution by providing
correct air or liquid distribution.
HIGH SUCTION PRESSURE-HIGH SUPERHEAT
Internally leaking compressor Locate leak. Repair/ replace.
HIGH SUCTION PRESSURE-LOW SUPERHEAT (DEFECTIVE UNLOADER)
Valve superheat setting too low. Adjust superheat as outlined under "Superheat
Adjustment".
Compressor discharge valves leaking. Replace or repair discharge valve.
Incorrect superheat adjustment.
Superheat adjustment 12 to 16ï‚°F.
FLUCTUATING DISCHARGE PRESSURE
Insufficient charge. Add R-134a to system.
HIGH DISCHARGE PRESSURE
Air or non-condensable gases in condenser. Purge and recharge system.
Overcharge or refrigerant. Recover to proper charge.
Condenser dirty. Clean condenser.
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