AAON M1-011 - Manual (Page 36)

12. Troubleshooting
Common Problems
Table 12.1, Problems, Causes, & Solutions
Problem Possible Cause Solutions
Frosted evaporator coil, low
suction pressure
Restricted air flow
Low fan speed
Reversed blower rotation
Low refrigerant charge
Clean, or replace filters
Check fan drives
Correct wiring
Add refrigerant
Unit runs, but supplies warm air Loss of refrigerant
Dead expansion valve element
Plugged filter-drier
Check leaks, add refrigerant
Replace valve element
Replace filter-drier
Compressor starts, but opens
high pressure control Refrigerant over-charged
Air in condenser coil
Condenser fan dead
Condenser coil dirty
Remove some refrigerant
Evacuate and recharge refrigerant
Replace fan motor
Clean condenser coil
High suction pressure, but low
superheat Oversized expansion valve
Poor sensing bulb location
Low superheat adjustment
Replace with correct expansion valve
Relocate sensing bulb, secure to suction line
Adjust expansion valve
Unit operates continuously Low refrigerant charge
Unit undersized
Check and recharge to nameplate
Decrease load or resize unit
Thermostat set too low, increase temperature setting
Compressor Checkout
Poor Cooling - Compressor Runs or Cycles
36
High Head
Pressure
Low Head,
High Suction
Pressure
Low Suction
Pressure
Defective Compressor Valves
Bad Expansion Valve Power Element
Poor Airflow at Evaporator
Low Refrigerant Charge
Restriction in Feeder Tube
Dirty Condenser Coil (Low Airflow)
Poor Airflow at Condenser
Refrigerant Overcharge
Air in Refrigerant Circuit
Replace
Compressor
Diagnose &
Repair
Diagnose &
Repair