Mueller E-Star OESE 3.5 and 5 HP HFC Condensing Unit
Installation and Operation Manual, Part No. 8828747 Effective April 13, 2020
4.1 REFRIGERANT CYCLE
Mueller E-Star OESE condensing units utilize an thermal expansion valve (TEV) that controls the evaporator’s
superheat. The expansion valve must be field adjusted to maintain the milk coolor’s evaporator’s superheat at
4–6°F (2.2–3.3°C) or the chiller’s superheat at 10–12°F (5.6–6.7°C).
Refer to Figure 2, “Refrigeration Piping Schematic.” Subcooled liquid refrigerant leaves the condenser coil and
flows through the heat exchanger coil in the accumulator, where it is subcooled an additional 5–15°F (2.7–8.5°C).
This heat exchange also evaporates any liquid refrigerant in the suction accumulator, protecting the compressor
against liquid flood-back.
As the liquid refrigerant, now subcooled a total of 10–25°F (5.6–13.9°C), passes through the expansion valve, its
pressure is reduced to an evaporative pressure. Since the liquid refrigerant was subcooled in the accumulator
heat exchanger coil before entering the evaporator, there will be less flash gas at the inlet of the expansion valve.
Any liquid refrigerant returned from the evaporator is evaporated into vapor when it contacts the warmer heat
exchanger coil in the bottom of the suction accumulator. Vapor leaving the accumulator heat exchanger will be
superheated an additional 2–5°F (1.1–2.8°C) prior to entering the compressor’s suction intake. This minimal
superheat provides protection against liquid refrigerant entering the compressor, while providing exceptional
refrigerant cooling of the compressor.
4.2 OIL RETURN
Refrigerant oil returning from the evaporator drops into the accumulator where the oil separates from the
refrigerant and settles to the bottom of the accumulaotr. This oil is metered back into the compressor through
the oil pickup orifice, located in the bottom of the accumulator’s suction outlet “J” tube. Refer to Section 6.0,
“Accumulator Heat Exchanger.”
4.3 INCREASED OPERATING EFFICIENCY
Mueller E-Star OESE condensing units incorporate a receiver and condenser subcooling loop to maintain proper
subcooled liquid refrigerant to the TEV, which ensures optimum evaporator efficiency.
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Section 4.0 – Operating Features
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