Operation - Rheem 55027500 Service Instructions Manual

Operation

Normal Operation
The 550 and 551 series heat pump water heaters utilise either R22 or R409A refrigerant to
transfer heat from the atmosphere to the water stored in the cylinder.
When the compressor thermostat contacts close the compressor and evaporator fan motor
commence operation. The action of the compressor creates a pressure difference that
causes the refrigerant to circulate through the sealed refrigeration system.
The refrigerant enters the evaporator as a liquid, as heat is absorbed from the atmosphere
by the refrigerant it changes state, at low pressure, from a sub cooled liquid to a super
heated vapour or gas (evaporates). The vapour then enters the compressor and obtains
more heat, known as heat of compression, and passes into the spiral condenser (heat
exchanger) as a super heated vapour at high pressure.
The spiral condenser (heat exchanger) is fixed in close contact to the inner wall of a tube
fitted in the centre of the cylinder. As the refrigerant passes through the condenser it gives
off heat to the cylinder surface, which is absorbed by the water. As the refrigerant gives off
heat it cools and changes state back into a liquid (condenses). The refrigerant then enters
the evaporator again and the cycle is repeated.
A metering device, called a TX valve, is positioned between the condenser and evaporator
to control, or meter the flow of refrigerant into the evaporator. The TX valve senses the
temperature of the suction line and automatically meters the flow of refrigerant based on
the detected temperature.
Defrost Operation
At low ambient air temperatures, typically below 10ºC, it is possible for the evaporator to
freeze.
55027500
If an evaporator surface temperature of –3.5ºC is detected a thermostat, called the de-ice
thermostat, activates a bypass solenoid. This solenoid allows a proportion of super heated
vapour from the compressor to bypass the condenser and directly enter the evaporator
assisting the evaporator to defrost. The De-ice thermostat opens at 3 degrees, which
causes the solenoid to close cutting of the supply of super heated vapour to the bypass
pipe, at this point normal heat pump operation is resumed.
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If an evaporator surface temperature of –3.5ºC is detected a thermostat, called the
evaporator thermostat, cuts power to the compressor and evaporator fan and activates the
booster element. The booster element is controlled by a Robertshaw thermostat and will
provide 130L of hot water. During this period the evaporator will naturally defrost. The
evaporator thermostat opens at 7 degrees, cutting power to the booster element and
reactivating the compressor and evaporator fan motor, at this point normal heat pump
operation is resumed.
TM017 Rheem Air Sourced Heat Pump Service Instructions REV: C
4
Date of Issue: 5/11/05
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