Pump down system

For some systems like heat pumps, a single pump down system (also called "pump out control") may be applied. The principle is the same as for an automatic pump down system (also called "pump down control"): extracting refrigerant on the evaporator side and shutting off the compressor via the low pressure switch. However, an additional auxiliary contactor ensures that after a single extraction of refrigerant and compressor shut-off, no further pumping cycles are possible. Restarting is only possible by demand from the room thermostat or after completion of a defrost cycle.

• Automatic pump down system: repeated extraction of refrigerant
• Single pump down system: one-time extraction of refrigerant

Regardless of the system, it is important to respect the minimum pressure settings and avoid operation in vacuum.

In case of using water as coolant, consider minimum pressure limits refering to a saturated temperature >0°C of the refrigerant to avoid damaging the heat exchanger.

• For the low pressure setting, consider the minimum pressure refering to the lowest evaporation temperature of the application limits (all pressure values refer to gauge pressure):
• 2.1 bar(g) for R454B and R452B
• 2.4 bar(g) for R410A and R32
• 0.6 bar(g) for R290
• In order to avoid unnecessary low pressure cut-outs, a second lower value may be set, which may not fall below 1.0 bar (0.1 bar for R290).

Additionally, operation in this range of 2.1 .. 1.0 bar (R454B and R452B) resp. 2.4 .. 1.0 bar (R410A and R32) resp. 0.6 .. 0.1 bar (R290) is limited to max. 60 s during compressor start. For further guidance, please consult Bitzer.

For pump down, the use of an external check valve is recommended.