Rheem A18AZ Series - Page 42

42
Table 18: Service Analyzer Chart (cont.)
ELECTRONIC EXPANSION VALVES
SYMPTOM POSSIBLE CAUSE REMEDY
High Superheat, Low
Suction Pressure
(superheat over
15°F [8.3°C])
Moisture freezing and blocking valve
Recover charge, replace lter-drier, evacuate system,
recharge.
Dirt or foreign material blocking valve Recover charge, replace lter-drier, evacuate system, recharge
Low refrigerant charge Correct the charge.
Vapor bubbles in liquid line
Remove restriction in liquid line. Correct the refrigerant charge.
Remove noncondensible gases.
Size liquid line correctly.
Undersized EXV Replace with correct valve.
Incorrectly sensing vapor line temperature
Verify suction thermistor resistance is correct and properly
attached and insulated to the vapor line.
Suction thermistor incorrectly calibrated. Replace suction thermistor assembly.
Vapor 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 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.
EXV is stuck
Remove EXV from the system and purge with nitrogen,
replace lter drier, and recharge.
If EXV will not open, validate EXV wiring harness and rotor
resistance between the black wire and the other 4 wires.
If none of the above recties the issue, replace EXV and lter drier
and recharge.
UODC DC circuit failed
Verify 5VDC to pressure transducer is present. If not,
replace UODC.
High superheat adjustment Change the superheat offset dip switches to increase superheat.
Valve feeds too much
refrigerant, with low
superheat, with low
superheat and
higher than normal
suction pressure.
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 UODC 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, with insulation.
Low superheat adjustment Change the superheat offset dip switches to increase superheat.
Incorrectly sensing vapor line temperature
Verify suction thermistor resistance is correct and
properly attached and insulated to the vapor line.
Suction thermistor incorrectly calibrated. Replace suction thermistor assembly.
Vapor 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 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.
Low load
Reduced airow
Dirty lter
Dirty coil
Wrong duct size
Restricted duct
Thermostat setting Advise customer.