Defrost cycle

Air Conditioning and Heat Pumps · Heat Pumps in Practice · printed page 229 (PDF page 230)

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Defrost Cycle in Heat Pumps Heat Pump – Defrost Cycle

Text in the illustration

warmed refrigerant to the refrigerant flow temperature, air pressure or refrigerant pressure sensors located at the outdoor coil
A
the reversing valve is activated - sending warmed refrigerant to the outdoor coil to melt the ice
indoor coil
blower
electric heating element
check valve
reversing valve
heat pump compressor
outdoor coil
fan
frost
B
the outdoor fan is turned off
C
if electric heating elements are present, one stage is activated to warm the air coming off the blower
if there is no electric heat, the indoor blower is shut off
note:
the defrost cycle may be initiated by timer or temperature, air pressure or refrigerant pressure sensors located at the outdoor coil
in some units, reverse flow defrost is not used (the ice is melted by an electric heater at the outdoor coil)
= refrigerant flow

Generated explanation

The schematic shows a heat pump operating in its defrost cycle, with red and blue refrigerant piping connecting the compressor, reversing valve, indoor coil, outdoor coil, and check valves. The reversing valve directs warmed refrigerant to the frost-covered outdoor coil to melt ice, illustrated by water droplets beneath the coil. A prohibition symbol over the outdoor fan indicates that it is turned off during defrost. At the indoor coil, an electric heating element warms air leaving the blower when electric heat is available; otherwise, the annotation specifies that the indoor blower is shut off. Notes identify timer- or sensor-initiated defrost and an alternative arrangement using an electric heater at the outdoor coil.

Components

indoor coil outdoor coil indoor blower outdoor fan electric heating element heat pump compressor reversing valve check valves refrigerant piping

Materials

refrigerant frost ice water