SECTION 22: HEATING AND AIR CONDITIONING
38
DOB 2490-2789 | X3-45 Commuter PA1605 Maintenance Manual (Final Version – Rev.2 April 2016)
7.12 TROUBLESHOOTING
7.12.1 Expansion Valve
PROBABLE CAUSE
PROBABLE REMEDY
LOW SUCTION PRESSURE-HIGH SUPERHEAT
E
XPANSION
V
ALVE
L
IMITING
F
LOW
:
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 or clean filter-dryer.
Inlet pressure too low from excessive low
condensing temperature. Resulting pressure
difference across valve too small.
Increase head pressure. Verify pressure switch
for fan speed control.
Superheat adjustment too high.
Adjust superheat as outlined under "Superheat
Adjustment".
Power assembly failure or partial loss of charge.
Replace power assembly or replace valve.
Air filter screen clogged.
Clean or replace air filter.
Plugged 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
Compressor discharge valve leaking.
Replace or repair valve.
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 16°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.
Bleed to proper charge.
Condenser dirty.
Clean condenser.
