American Power Conversion FM, DX manual Problem Possible Cause Corrective Action

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

NetworkAIR FM DX 60 Hz Operation, Maintenance, and Troubleshooting 79