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79NetworkAIR FM DX 60 Hz Operation, Maintenance, and Troubleshooting
Suction pressure too
low
• Dirty or blocked evaporator coil
• Dirty or blocked air filters
•Low airflow
• Low return air temperature
• Low refrigerant charge
• Liquid line filter drier is blocked
• High evaporator superheat
• Clean evaporator coil.
• Check filters and replace as needed.
• Check for correct airflow setting.
• Verify the return air temperature is not below
20ºC (68
°F).
• Check for short cycling of cold supply air.
• Check subcooling and ensure it is at least
10-15
°F. Repair leak and recharge system
• Check filter drier for excessive pressure drop.
• Check for proper superheat and TXV
operation.
System short of
capacity
• Low refrigerant charge
• Liquid line filter drier is blocked
• High evaporator superheat
• Insufficient air quantity across the
evaporator coil
• Excessive outside air infiltration
• Lack of proper room vapor barrier
• Check subcooling and ensure it is at least
10-15
°F. Repair leak and recharge system.
• Check filter drier for excessive pressure drop.
• Check for proper superheat and TXV
operation.
• Check for correct airflow and clean filters.
• Reduce outside air infiltration.
• Install vapor barrier materials on floor, walls,
and ceiling as needed.
Temperature control
not tight enough
• Excessive outside air infiltration
• Lack of proper room vapor barrier
• Cool/reheat setpoints not close
enough
• Reheat PID loop is not properly
tuned
• Interstage delay is too large
• Return air temperature does not
reflect actual room condition
• Reduce outside air infiltration.
• Install vapor barrier materials on floor, walls,
and ceiling as needed.
• Check cooling and reheat setpoints and
deadbands.
• Tune the PID loop for accurate reheat
operation.
• Reduce the interstage delay to allow quicker
response to temperature changes.
• Check for short cycling of cold supply air.
• Check air distribution for deficiencies.
• Consider using remote sensor control.
Note: Be certain to purchase the correct
temperature and humidity probe. Check when
ordering that your equipment is compatible.
Water carryover • Dirt or oil residue on evaporator
coil
• Insufficient air quantity across the
evaporator coil
• Excessive airflow across the
evaporator coil
• Blockage in condensate pan or
drain line
• Low return air temperature
• High return humidity
• Excessive outside air infiltration
• Lack of proper room vapor barrier
• Clean the evaporator coil.
• Check for correct airflow and clean filters.
• Reduce airflow to specifications.
• Clean condensate pan and drain line.
• Verify the return air temperature is not below
20ºC (68ºF).
• Check for short cycling of cold supply air
• Lower humidity setpoint.
• Check for short cycling of supply air
• Reduce outside air infiltration.
• Install vapor barrier materials on floor, walls,
and ceiling as needed.
Problem Possible Cause Corrective Action