47
10.7
Service Analyzer Chart (cont.)
Diagnostics
ELECTRONIC EXPANSION VALVES
SYMPTOM POSSIBLE CAUSE CHECK OR REMEDIES
EXV feeds too
much refrigerant,
with low super-
heat, with low
superheat and
higher than normal
suction pressure
EXV control dc circuit failed Verify 5Vdc to pressure transducer is present, if not,
replace EXV controller
High superheat adjustment Change the superheat offset dip switches to increase
superheat
Moisture causing valve to stick open Recover refrigerant, replace lter-drier, evacuate system
and recharge
Dirt or foreign material causing valve to stick open Recover refrigerant, replace lter-drier, remove EXV and
purge with nitrogen, evacuate system and recharge
If EXV is completely clogged, use the EXV control to
open the EXV, and purge with nitrogen, replace lter
drier, and recharge
Oversized EXV Install correct EXV
Incorrect suction thermistor location Install suction thermistor with the provided stainless steel
strap and an additional zip tie between the 10:00 and
2:00 position on suction line, and insulate
Low superheat adjustment Change the superheat offset dip switches to increase
superheat
Incorrect sensing suction line temperature Verify suction thermistor resistance is correct and proper-
ly attached and insulated to the suction line
Suction thermistor incorrectly calibrated Replace suction thermistor assembly
Suction pressure measured incorrectly After verifying lack of connectivity, replace the pressure
transducer or harness
If harness has a short, replace harness
If gauge pressure measurement and the converted volt-
age readings at the control are different replace pressure
transducer
If gauge pressure measurement and the converted
voltage readings at the control are the same, replace the
control
Compressor ood
back upon start-up
Refrigerant drained from ooded evaporator Install trap riser to the top of the elevator coil
Inoperable crankcase heater or crankcase heater
needed
Replace or add crankcase heater
Any of the causes listed under symptoms of elec-
trical problem in section 10.3
Any of the solutions listed under solutions of electrical
problems in section 10.3
Superheat is low
to normal with low
suction pressure
Unequal evaporator circuit loading Ensure airow is equally distributed through evaporator
Check for blocked distributor tubes
Low load or airow entering evaporator coil Ensure blower is moving proper air-ow
Remove/correct any airow restriction
10.0 DIAGNOSTICS AND TROUBLESHOOTING
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