Filling refrigerant in an air source heat pump is essential for keeping the system efficient. Without the correct amount of refrigerant, the heat pump may fail to heat or cool properly, leading to higher energy bills, poor performance, and potential damage to the compressor. Adding refrigerant must be done carefully to avoid overcharging or undercharging, which can impact the heat pump's lifespan.
This guide covers everything you need to know about refilling refrigerant in an air source heat pump, including how to add refrigerant safely, how much refrigerant is safe for a heat pump, and why refrigerant charge must be within recommended safety limits.
Refrigerant is a chemical compound used in heating and cooling systems to transfer heat. It changes from a liquid to a gas and back to absorb and release heat, making it essential for maintaining comfortable indoor temperatures.
A heat pump works by moving heat rather than generating it. The refrigerant inside the system absorbs heat from the outdoor air (even in cold weather) and transfers it indoors for heating. In cooling mode, it does the opposite—removing heat from inside and releasing it outdoors.
| Refrigerant Type | Common Uses | Environmental Impact | Efficiency |
|---|---|---|---|
| R410a | Older residential heat pumps | High GWP (2088) | Good |
| R32 | Found in modern air source heat pumps | Lower GWP (675), more efficient than R410a | Better |
| R290 (Propane) | Eco-friendly systems | Ultra-low GWP (3), flammable | High |
* different refrigerants digram
Why does refrigerant choice matter?
R32 and R290 are replacing R410a due to their lower global warming potential (GWP) and improved efficiency.
Additionally, knowing the characteristics of each refrigerant is crucial for safe refrigerant adding and ensuring the correct refrigerant charge within the recommended safety limits.
Not every performance issue means your heat pump needs refrigerant. Before adding refrigerant, check for these signs:
Reduced heating or cooling efficiency – The system takes longer to reach the desired temperature.
Frozen evaporator coils – Ice buildup on coils indicates low refrigerant levels.
Unusual hissing or bubbling sounds – These noises could mean there is a leak.
Higher electricity bills – A struggling heat pump consumes more energy.
Short cycling – The heat pump turns on and off too frequently.
Inconsistent air temperature – The system struggles to maintain a stable output.
Increased system wear and tear – Low refrigerant can strain components, leading to failures.
Pro Tip: If there is a refrigerant leak, adding refrigerant will not solve the problem. Leaks must be repaired first.
Refrigerant gauge manifold – Measures system pressure.
Vacuum pump – Removes air and moisture before charging.
Refrigerant tank (R410a, R32, or R290).
Protective gloves & safety goggles – Prevents refrigerant exposure.
Thermometer – Ensures the correct temperature differential.
Step 1: Turn Off the Heat Pump – Always power off the unit before adding refrigerant.
Step 2: Connect the Gauge Manifold – Attach the low-pressure side to the service port.
Step 3: Check for Leaks – If leaks are found, repair them before proceeding.
Step 4: Remove Moisture with a Vacuum Pump – Run the vacuum pump for at least 15–30 minutes.
Step 5: Slowly Add Refrigerant – Open the low-side valve and add refrigerant in small amounts.
Step 6: Monitor System Pressure – Ensure the refrigerant charge is within recommended safety limits.
Step 7: Test the System – Power the heat pump on and verify performance.
Step 8: Check for Proper Operation – Observe airflow and system cycles to confirm efficiency.
Warning: Never overfill refrigerant. Overcharging can damage the compressor and reduce efficiency.
Refrigerants have unique pressure-temperature characteristics. Use this chart while adding refrigerant:
| Temperature (°C) | R410a Pressure (bar) | R32 Pressure (bar) | R290 Pressure (bar) |
| -10 | 4.2 | 3.5 | 2.7 |
| 0 | 6.9 | 6.1 | 4.3 |
| 10 | 10.1 | 9.4 | 6.2 |
| 20 | 14.1 | 13.2 | 8.7 |
| 30 | 19.0 | 18.0 | 11.8 |
| 40 | 24.9 | 23.9 | 15.6 |
Data Sources:
Overfilling refrigerant – Can damage the system.
Using the wrong refrigerant – Always check the type needed.
Skipping vacuuming the system – Moisture can cause problems.
Not following safety steps – Always wear protective gear.
Ignoring manufacturer recommendations – Each system has specific refrigerant requirements.
Q1: Can I add refrigerant to my heat pump myself?
A: Some areas require EPA certification. Always check regulations before adding refrigerant.
Q2: How often does a heat pump need refrigerant?
A: A properly sealed system should not require frequent refilling. If refrigerant levels drop, there may be a leak.
Q3: How much refrigerant is safe for a heat pump?
A: Always stay within the recommended safety limits to avoid system damage.
Q4: What is the safest refrigerant to use?
A: R-32 and R-290 are more eco-friendly than R-410A.
Adding refrigerant to an air source heat pump must be done carefully. Using the right refrigerant, following safety procedures, and ensuring the correct charge can improve efficiency and extend system life.
Need expert help? Contact Solareast for professional HVAC solutions.