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Fujitsu FO20R Series Installation Instructions Manual page 70

Variable speed r-410a heat pump outdoor units
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9.0 DIAGNOSTICS & TROUBLESHOOTING
9.12 Service Analyzer Charts (cont.)
Valve feeds too much
refrigerant, with low
superheat, with low
superheat and
higher than normal
suction pressure.
Compressor flood
back upon
start-up
70
Moisture causing valve to stick open.
Dirt or foreign material causing valve to stick
open
Oversized EXV
Incorrect suction thermistor location
Low superheat adjustment
Incorrectly sensing vapor line temperature
Suction thermistor incorrectly calibrated.
Vapor pressure measured incorrectly.
Refrigerant drainage from flooded evaporator
Inoperable stator heat
Recover refrigerant, replace filter-drier, evacuate
system, and recharge.
Recover refrigerant, replace filter-drier, remove EXV
and purge with nitrogen, evacuate system, and recharge.
If EXV is completely clogged use the VSODC to open the EXV,
and purge with nitrogen, replace filter drier, and recharge.
Install correct EXV.
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, with insulation.
Change the superheat offset dip switches to increase
superheat.
Verify suction thermistor resistance is correct and
properly attached and insulated to the vapor line.
Replace suction thermistor assembly.
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
voltage 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.
Install trap riser to the top of the evaporator coil.

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