Why Is My Rooftop Unit Fan Running but Not Cooling?
If your rooftop unit (RTU) fan is running but the space is not cooling, the most common cause is that the compressor is not operating, even though the blower motor is functioning normally.
This condition usually indicates a refrigerant circuit or safety lockout issue rather than a fan failure.
Common Causes
The most frequent causes include:
- Tripped high-pressure or low-pressure switch
- Compressor contactor failure
- Blown fuse in compressor circuit
- Failed run capacitor
- Thermostat not calling for cooling
- Low refrigerant charge
- Control board lockout
How to Troubleshoot
1. Verify Thermostat Call
Confirm the thermostat is calling for cooling and sending a signal to the RTU.
2. Check Compressor Operation
Listen for compressor startup. If silent:
- Check contactor engagement
- Measure voltage at compressor terminals
3. Inspect Pressure Switches
If a safety switch is open, the compressor will not run.
Reset only after identifying root cause.
4. Check Refrigerant Pressure
Low suction pressure can trigger compressor lockout.
When to Call for Service
If:
- Breakers trip repeatedly
- Refrigerant pressures are abnormal
- Compressor hums but does not start
Professional service may be required.
FAQ
Why does the fan run but not the compressor?
The blower is often on a separate control circuit and may continue running during faults.