Pentair UltraTemp Low Refrig Alarm
The LOW REFRIG alarm on a Pentair UltraTemp indicates the refrigerant low pressure switch has opened. This means pressure in the refrigerant system has dropped below safe operating levels.
This alarm can be caused by refrigerant leaks, cold weather, or airflow restrictions across the evaporator coil.
Common Causes
Refrigerant Issues
- Low refrigerant charge: Leak in the system
- Refrigerant leak: At joints, valves, or heat exchanger
Environmental Conditions
- Air temperature too cold: Heat pumps have minimum operating temperatures
- Water temperature too cold: Below safe operating range
Airflow Problems
- Fan motor not running
- Bad fan capacitor
- Fan blade slipping or broken
- Debris blocking evaporator coil
- Shrubs or obstacles restricting airflow
Component Failures
- Bad low pressure switch
- TXV (thermal expansion valve) stuck closed
- Restricted filter drier
Troubleshooting Steps
Step 1: Check Environmental Conditions
- What is the outdoor air temperature?
- What is the water temperature?
- Heat pumps typically need air temps above 50F (10C) for heating
- If too cold, wait for temperatures to rise
Step 2: Inspect Fan Operation
- With heat pump running, verify fan is spinning
- Listen for unusual noises
- Check that fan blade is not slipping on shaft
- Verify fan blade is not cracked or damaged
Step 3: Check Fan Capacitor
- Turn off power to heat pump
- Locate fan capacitor
- Check for bulging, leaking, or damage
- Test capacitor with meter if available
- Replace if faulty
Step 4: Check Airflow
- Remove any debris from around unit
- Trim shrubs/vegetation to maintain clearances
- Check evaporator coil for dirt or debris
- Clean coil if needed (use coil cleaner)
Step 5: Check for Ice
Ice on evaporator coil indicates problems:
- Low refrigerant charge
- Restricted airflow
- Defrost cycle not working
Low Pressure Switch Test
If other troubleshooting fails:
- Turn off power to heat pump
- Locate low pressure switch
- With proper refrigerant charge, switch should be closed
- Check resistance - should have continuity when closed
- If open with proper charge, replace switch
When HVAC Tech is Needed
Call a licensed HVAC technician if:
- Refrigerant leak is suspected
- System needs to be recharged
- TXV appears to be stuck
- Filter drier needs replacement
- Compressor issues are suspected
Required Clearances
Proper clearances ensure adequate airflow:
| Location | Minimum Clearance |
|---|---|
| Sides | 24 inches |
| Top (discharge) | 48 inches |
| Back | 12 inches |
| Front (service access) | 24 inches |
Prevention
- Maintain proper clearances around unit
- Keep coils clean
- Trim vegetation regularly
- Have refrigerant charge checked annually
- Don't operate in temperatures below manufacturer limits