Expansion Valve - PREVOST H3-41 Maintenance Manual

SECTION 22: HEATING AND AIR CONDITIONING
5.7.2

Expansion Valve

PROBABLE CAUSE
E V L
XPANSION ALVE IMITING
Gas in liquid line due to pressure drop in the line
or insufficient refrigerant charge.
Superheat adjustment too high.
Power assembly failure or partial loss of charge.
Air filter screen clogged.
Plugged / kinked / chaffed lines.
Uneven or inadequate evaporator loading due to
poor air distribution or liquid flow.
Internally leaking compressor
HIGH SUCTION PRESSURE-LOW SUPERHEAT (DEFECTIVE UNLOADER)
Valve superheat setting too low.
Compressor discharge valves leaking.
Incorrect superheat adjustment.
Insufficient charge.
Air or non-condensable gases in condenser.
Overcharge or refrigerant.
Condenser dirty.
52 PA1621 Maintenance Manual All Series | Revised February 2019
LOW SUCTION PRESSURE-HIGH SUPERHEAT
F :
LOW
LOW SUCTION PRESSURE-LOW SUPERHEAT
HIGH SUCTION PRESSURE-HIGH SUPERHEAT
FLUCTUATING DISCHARGE PRESSURE
HIGH DISCHARGE PRESSURE
PROBABLE REMEDY
Locate cause of line flash and correct by use of
any of the following methods. Add R-134a.
Replace filter-dryer.
Adjust superheat as outlined under "Superheat
Adjustment".
Replace expansion valve.
Clean or replace air filter screen.
Clean, repair or replace lines.
Balance evaporator load distribution by providing
correct air or liquid distribution.
Locate leak. Repair/ replace.
Adjust superheat as outlined under "Superheat
Adjustment".
Replace or repair discharge valve.
Superheat adjustment 12 to 16°F.
Add R-134a to system.
Purge and recharge system.
Recover to proper charge.
Clean condenser.