Rheem PNL-*AZ Series Installation Instructions Manual page 29

THERMOSTATIC EXPANSION VALVES
SYMPTOMS
High Superheat, Low Suction Pressure
Valve feeds too much refrigerant,
with low superheat and higher than
mal suction pressure
Compressor flood back upon start up
POSSIBLE CAUSE
Moisture freezing and blocking valve
Dirt or foreign material blocking valve
Low refrigerant charge
Vapor bubbles in liquid line
Misapplication of internally equalized
valve
Plugged external equalizer line
Undersized TEV
Loss of charge from power
head sensing bulb
Charge migration from sensing bulb
to power head (Warm power head
with warm, wet cloth. Does valve
operate correctly now?)
Improper superheat adjustment
(Only applicable to TEV with adjustable
superheat settings)
Moisture causing valve to stick open.
Dirt or foreign material causing
valve to stick open
TEV seat leak (A gurgling or hissing
sound is heard AT THE TEV during
the off cycle, if this is the cause.)
NOT APPLICABLE TO BLEED
PORT VALVES.
Oversized TEV
Incorrect sensing bulb location
Low superheat adjustment
(only applicable to TEV with
adjustable superheat setting)
Incorrectly installed, or restricted
external equalizer line
Refrigerant drainage from flooded
evaporator
Compressor in cold location
Any of the causes listed under
Symptoms of Problem #2
CHECK OR REMEDIES
Recover charge, install filter-drier,
evacuate system, recharge
Recover charge, install filter-drier,
evacuate system, recharge
Correct the charge
Remove restriction in liquid line
Correct the refrigerant charge
Remove non-condensible gases
Size liquid line correctly
Use correct TEV
Remove external equalizer line
restriction
Replace with correct valve
Replace power head or complete
TEV
Ensure TEV is warmer than
sensing bulb
Adjust superheat setting counter-
clockwise
Recover refrigerant, replace filter-
drier, evacuate system and then nor-
recharge
Recover refrigerant, replace filter-
drier, evacuate system and
recharge
Replace the TEV
Install correct TEV
Install bulb with two mounting
straps, in 2:00 or 4:00 position on
suction line, with insulation
Turn superheat adjustment
clockwise
Remove restriction, or relocate
external equalizer
Install trap riser to the top of the
evaporator coil
Install crankcase heater on
compressor
Any of the solutions listed under
Solutions of Problem #2
29