49
Diagnostics
9.3 Service Analyzer Charts (cont.)
9.0 DIAGNOSTICS & TROUBLESHOOTING
THERMOSTATIC EXPANSION VALVES (cont.)
SYMPTOM POSSIBLE CAUSE REMEDY
Low load
Reduced airow
Dirty lter
Dirty coil
Wrong duct size
Restricted duct
Thermostat setting Advise customer.
Compressor ood
back upon start-up
Refrigerant drainage from ooded evaporator
Install trap riser to the top of the evaporator coil.
Inoperable stator heat
Superheat is low
to normal with low
suction pressure
Unequal evaporator circuit loading
Recover refrigerant, replace lter-drier, evacuate
system, and recharge.
Check for blocked distributor tubes.
Low load or airow entering evaporator coil
Ensure blower is moving proper air CFM.
Remove/Correct any airow restriction.
Superheat and
suction pressure
uctuate (valve
is hunting)
Expansion valve is oversized. Install correct TXV
Section thermistor is affected by liquid refrigerant
or refrigerant oil owing through suction line
Relocate sensing bulb in another position around the
circumference of the suction line.
Unequal refrigerant ow through evaporator
circuit
Ensure sensing bulb is located properly.
Check for blocked distributor tubes.
Moisture freezing and partially blocking TXV
Recover refrigerant, change lter-drier, evacuate
system, and recharge.
Valve does not
regulate at all
Pressure transducer not connected or plugged
Connect pressure transducer in proper location, or
remove any blockage.
Suction line thermistor not connected, or
installed on heat effected zone.
Install suction line thermistor in correct horizontal
clean section of copper pipe.
Suction line thermistor failed (continuity to
control, wire damaged, resistance values
incorrect)
Replace suction line thermistor.
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