AAON M2-036 - Manual (Page 67)

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2. Check for proper start-up and ignition as
outlined in Start-Up section.
3. Check the appearance of the burner flame.
4. Check that the circulating air fan is
operating and verify the proper airflow
through duct furnace.
5. Return thermostat or heat controller to
normal setting.
Troubleshooting
Table 11 - Problems, Causes and 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
Faulty 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 faulty
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