Sometimes the reason why your Aaon rooftop unit is misbehaving is as obvious as the storm rolling along outside your window, but other times, power surges, blown fuses or other electrical problems may be causing your Aaon rooftop unit to stop working. In this Aaon rooftop unit troubleshooting guide, we’ll walk both building owners and HVAC technicians through what they can do to turn the air or heat back on.
What Is the First Step in Troubleshooting an Air Conditioning System?
Before you call an HVAC technician, you can ask yourself these common Aaon rooftop unit troubleshooting questions that are simple enough for any building owner or manager to do, with no multimeters or dismantling required:
- Is the thermostat set to the right temperature? – Being in the midst of one of those unseasonable cold snaps or warm spells can cause the building to feel hotter or colder than it normally would. Also, never write off employee interference – they might have given the thermostat a little nudge in either direction. So if your Aaon RTU isn’t cooling or heating, you might want to check that the thermostat is set to an appropriate temperature.
- Is the thermoset set to the correct mode? – Maybe the thermostat is set to the desired temperature, but it’s switched to the wrong mode. 72℉ feels a lot different if it’s cooling vs. heating, so just take a second to make sure everything checks out.
- Is there power to the thermostat? – It’s pretty easy to tell if your Aaon thermostat doesn’t have power because you’ll be staring at a blank screen. Ensure the circuit breaker supplying power to the thermostat hasn’t been tripped. If yours is a battery-operated thermostat, you could also try replacing the batteries with a fresh set.
- Is there power to the rooftop unit? – To fix this issue, ensure the circuit breaker supplying power to your RTU hasn’t been tripped.
Aaon Rooftop Unit Troubleshooting: Electric Heating
Problem | Solution |
Unit won’t turn on
|
- Check the power at the contactor(s) line side
- The thermostat is not set to heating
|
Evaporator motor won’t turn on
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- The overload relay has tripped
- The heater relay is not energized
- The blower contactor is not energized
- There is an open or short circuit in the capacitor (PSC motors only)
|
Blower not working
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- The blower’s direction is reversed
- The air filters are dirty
- The condenser/evaporator coils are dirty
- The ducts are dirty or obstructed
|
Blower turns on but no heat
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- The heater contactor(s) are open
- The limit switches are open
- The heater relay is open
- The heat strips are burnt out
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Aaon Rooftop Unit Troubleshooting: Gas Heating
Problem | Solution |
Unit won’t turn on
|
- Ensure there is power and gas
- Double Check the thermostat is set to the right temperature and mode
- Check there is 24 volt power to the ignition control
|
The burner won’t turn on
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- Ensure the main gas valve has power
- The gas valve is broken
- The gas valve’s connections are loose
- Check if the limit controls are open
- Replace the the differential pressure switch if it’s open
- The ignition control is faulty
|
Combustion air blower not working
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- The thermostat is not set to heating mode
- The relay won’t close (no power to motor)
- The motor is faulty
- The internal motor overload is open
|
Burner goes “off” on high limit
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- If the blower is not turning on, check the fan control
- The blower motor’s direction is reversed
- The filters are dirty
- The ducts are obstructed or the dampers are closed
- The manifold gas pressure is too high
|
Ignition is on but burner won’t ignite
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- If the hand valve is in the “off” position, turn it on
- The gas is off or the pressure is too low
- Ensure that the main gas valve has power
- Replace the the differential pressure switch if it’s open
- Sparker sensor is out of alignment
- The main orifice is blocked
|
Supply fan blower isn’t working
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The ignition control is faulty
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Aaon Rooftop Unit Troubleshooting: Steam & Hot Water Heating
Problem | Solution |
Unit won’t turn on
|
- Check the power at the contactor(s) line side
- The thermostat is not set to heating
|
Blower won’t start
|
- The overload relay has tripped
- The heater relay is not energized
- The blower contactor is not energized
|
Blower won’t deliver air
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- The blower’s direction is reversed
- The air filters are dirty
- The condenser/evaporator coils are dirty
- The ducts are dirty or obstructed
|
Blower turns on but no heat
|
- Inspect the steam traps, valves and steam or hot water to ensure they adhere to the manufacturer’s guidelines
- The thermostat is defective
|
Aaon Rooftop Unit Troubleshooting: Cooling Package and Units with Remote Condensers
Problem | Solution |
Unit won’t turn on
|
- Check the power at the contactor(s) line side
- The thermostat is not set to heating
- The high pressure control has tripped
- The low pressure switch is open (loss of charge)
|
Condenser fan not running
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- The motor’s overload thermal protector is open
- There is a short or an open in a the motor’s run capacitor
- The motor is faulty
- Something is obstructing the fan or its shaft
|
Evaporator blower not running
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- The motor’s overload thermal protector is open
- The relay won’t close
- The motor is faulty
- There is a short or an open in the capacitor (PSC motors only)
- Something is obstructing the shaft or blower wheel
|
Compressor short cycling
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- The refrigeration charge might be too low
- Check the compressor overload setting
- The ambient temperature is too low
- The filters are dirty
- The evaporator blower isn’t running
|
Fan motor runs hot then stops
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- The line voltage is too high
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Compressor not turning on
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- The line voltage is too low
- There is an open in the limit switches
- There is an overload or the pressure control has tripped
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Blower won’t deliver air
|
- The blower’s direction is reversed
- The filters are dirty
- The duct is obstructed
|
Aaon Rooftop Unit Troubleshooting: Cooling - Chilled Water
Problem | Cause |
Unit won’t turn on
|
- Check the power at the contactor(s) line side
- The thermostat is not set to heating
|
Evaporator blower not working
|
- The motor’s overload thermal protector is open
- The contactor is not closed
- The motor is faulty
|
Fan motor runs hot then stops
|
- The line voltage is too high
|
Blower won’t deliver air
|
- The blower’s direction is reversed
- The air filters are dirty
- The duct is obstructed
|
Blower turns on but won’t cool
|
- Verify there is a water supply and it’s at the right temperature
- Ensure the water control valves are working properly
- Examine the water temperature rise as it enters and exits the unit to see if enough water is flowing
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Common Aaon Rooftop Unit Alarm Codes
Problem | Cause |
FLT: LAT Probe A
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There is an open or short in the LATA probe
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FLT: LAT Probe B
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There is an open or short in the LATB probe
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FLT: OAT Probe
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There is an open or short in the OAT probe
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FLT: LAT Hi Limit
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Exiting air temperature is too high
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Hi LAT Cooldown
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The unit is still cooling down after a high limit event
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LATbelow Lo Limit
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LAT is below the low limit
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Mech Lmt Recovery
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Stage 1 only recovery after a mechanical limit
|
Mech Lmt Shutdown
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The rooftop unit shut down after too many high limit events |
FLT: SCR 0-10
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There is an overload or short on the 0-10VDC analog signal output
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BB (Base Block)
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The 24V enable is not being received
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Motor Overload oL1 or Drive Overload oL2
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The load is too large The cycle times are too short for the accel and decel
|
Check out our Aaon air handler troubleshooting article for more pointers on other Aaon HVAC units.
Please contact a local authorized service agent who can help with this specific unit and all your heating and cooling needs.
