Monday, April 8, 2019

How to Charge a Heat Pump in the Winter

hvac system

Heat pumps use refrigerant to transfer heat between the inside of your home and the outdoors. When refrigerant lines are damaged, refrigerant can leak out of the system. The heat pump will need to be recharged to restore the proper amount of refrigerant necessary for optimal performance.

Charging Heat Pumps in Cold Weather

Charging heat pumps in cold weather requires the superheat method, performed by trained HVAC technicians. Superheat refers to the difference between the refrigerant vapor’s actual temperature and its saturation temperature at the same point
To prevent the home from becoming cold, the auxiliary heating system will run while the heat pump is taken offline for repair. Charging heat pumps in cold weather is a difficult process because there is little latent heat load surrounding the system’s evaporator. The heat pump’s refrigerant charge won’t be perfect, but levels will be close, providing efficiency.

How to Charge a Heat Pump in the Winter

How to charge a heat pump in the winter is as follows:

  • The condenser is blocked using plastic sheeting to prevent air from leaving the system.
  • The heat pump is set to cooling mode by changing the position of its 4-way reversing valve. The low voltage wire is removed to force the heat pump to run in cooling mode for repair even though the thermostat calls for heat, which is provided by the auxiliary heating system.
  • Air is bled from the refrigerant lines containing refrigerant vapor.
  • A refrigerant cylinder is attached to the gauge lines to capture the refrigerant. It is turned upside down, then the manifold valve is opened on the system’s liquid line, allowing refrigerant liquid to flow into the line and move to the indoor and outdoor coil.
  • When the refrigerant liquid stops flowing, the valves are shut and the cylinder is placed in a bucket of tap water. This keeps the cylinder’s temperature at a temperate appropriate for keeping pressure up while charging refrigerant vapor into the heat pump – cylinder pressure can quickly drop during the refrigerant vapor charging process.
  • The superheat of the heat pump is measured. Liquid temperature of refrigerant boiling within the evaporator is measured via suction gauge, as well as the temperature of refrigerant coming out of the evaporator coil.
  • Head and suction line pressures are monitored and compared to the system’s superheat in order to determine an accurate charge.
  • Once the system has been charged, the plastic sheeting is removed from the condenser and orange low voltage wire replaced to switch the heat pump back to heating mode.
  • The system’s gauges are monitored for normal operating conditions.

HVAC technicians use the superheat method when charging heat pumps in cold weather. Because the outdoor coil operates at a lower temperature due to its size compared to the indoor coil, system responsiveness is lowered when attempting to charge a heat pump operating in heating mode. The superheat method has provided proper refrigerant charging in outdoor temperatures down to 20°F.


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