An air conditioner has a refrigerant circuit filled with a predetermined amount of a refrigerant, the circuit being formed of an outdoor unit and an indoor unit connected to each other by refrigerant piping, the outdoor unit having a compressor, an outdoor heat exchanger, and an expansion valve, the indoor unit having an indoor heat exchanger. The conditioner has an estimation model that estimates an amount of remaining refrigerant remaining in the circuit by using at least rotation frequency of the compressor, refrigerant discharge temperature at the compressor, heat exchanger temperature, degree of opening of the expansion valve, and outside air temperature, of operation state quantities indicating operation states during operation. The indoor heat exchanger has a sensor that is provided at an indoor heat exchanger intermediate portion connecting a first indoor heat exchanger port and a second indoor heat exchanger port to each other.

Methods and systems are provided for an air conditioning system. An example method of determining current through a compressor suction valve in a vehicle air conditioning (AC) system is provided, the AC system comprises an evaporator fan and the method includes determining the speed of the evaporator fan and determining the current through the suction valve based on the speed of the evaporator fan.

A monitoring and/or control device for an environmental control unit such as a heat pump determines the performance status and whether maintenance is required of a component of the unit for example a compressor during operation of the component. The device includes sensors configured to be situated relative to the compressor so as to receive and signal data from the compressor during operation of the component. In some embodiments, the device includes a vibration detector and a controller coupled to the vibration detector. The controller is configured to (i) receive electrical signals from the vibration detector, (ii) compare the electrical signals to a reference signal, (iii) determine the performance characteristic of the component based on the results of the comparison, and (iv) output a signal corresponding to the performance characteristic of the component to a user display. The controller may also request maintenance and/or order parts automatically.

A refrigeration cycle apparatus comprises a refrigerant circuit, a water circuit, and a control device. The refrigerant circuit includes a compressor, a four-way valve, a heat exchanger, a fan, a diaphragm mechanism, a water heat exchanger, and an accumulator. Based on a value of a low-pressure sensor or a high-pressure sensor and a water temperature on an outlet side of the water heat exchanger, the refrigeration cycle apparatus determines whether or not there is an abnormality due to dirtiness adhered to a plate inside the water heat exchanger.

A cooling device using a refrigeration cycle in which a refrigerant is circulated through a heat receiver, a compressor, a heat radiator, and an expansion valve includes: a gas-liquid separator configured to perform gas-liquid separation on the refrigerant supplied from the expansion valve; a pump configured to send a liquid phase refrigerant separated by the gas-liquid separator to the heat receiver; and a control unit configured to control opening and closing of a refrigerant flow path of the refrigeration cycle, and an operation and stop of the compressor and the pump, wherein the control unit starts the operation of the pump on condition that a net positive suction head of the pump has reached a predetermined value or more.

An HVAC system includes an evaporator coil and a compressor fluidly coupled to the evaporator coil. A condenser coil is fluidly coupled to the compressor. The condenser coil includes at least one condenser circuit fluidly coupled between a discharge line and an exit manifold. A sub-cool circuit is fluidly coupled between the exit manifold and a liquid line. A first temperature sensor is disposed at an entrance to the sub-cool circuit. A second temperature sensor is disposed at an exit to the sub-cool circuit. An HVAC controller is operatively coupled to the first temperature sensor and the second temperature sensor. The HVAC controller is configured to determine a temperature difference across the sub-cool circuit.

Disclosed are a carbon dioxide overlapping type heating system and a control method therefor. The heating system comprises a low-temperature stage loop, a high-temperature stage loop and a heat supply loop, wherein a low-temperature stage compressor (3) and a high-temperature stage compressor (7) are both variable-frequency compressors; and a water pump (10) is a variable-frequency water pump.

A method may include selecting a first set of values for a first set of parameters of one or more hardware components of an ice-making machine; identifying a water temperature at a water inlet of the ice-making machine; identifying an ambient air temperature surrounding the ice-making machine; calculating a second set of parameters of the ice-making machine based on at least a portion of the first set of values, the water temperature and the ambient temperature, the second set of parameters corresponding to operation of the ice-making machine in a freeze mode in which liquid water is cooled by an evaporator; and calculating a third set of parameters based on at least a portion of the first set of values, the water temperature and the ambient temperature, the third set of parameters corresponding to operation of the ice-making machine in a harvest mode.

An oil return control method for a multi-split air conditioner and a system accomplishing the same includes: calculating an average exhaust pressure within an oil return period Pd_AVG; determining whether the average exhaust pressure Pd_AVG≥the set threshold Pd.sub.threshold; if Pd_AVG≥Pd.sub.threshold, maintaining the multi-split air conditioner working in heating mode to ensure an acceptable oil return performance without affecting the air conditioning effect of indoor unit in heating mode; if Pd_AVG<Pd.sub.threshold, switching the multi-split air conditioner to cooling mode, stopping a fan within those power-on indoor units and entering into a cooling oil return process and switching the multi-split air conditioner back to heating mode until the cooling oil return process ends.

A refrigeration appliance with multiple storage compartments has a refrigerant circuit with a first expansion valve, a first heat exchanger, a second expansion valve, and a second heat exchanger connected in series between pressure and suction connections of a compressor. Each heat exchanger is associated with at least one storage compartment in order to control its temperature. A control unit controls the compressor rotational speed and positions of the expansion valves. The control unit has a continuously linear regulator for each storage compartment with a P-component for estimating a required temperature control output using a difference between actual and target temperatures. A model computing unit ascertains a target evaporation temperature for a first storage compartment controlled by the first heat exchanger, and for a second storage compartment controlled by the second heat exchanger. The heat exchangers are operated by selecting the compressor rotational speed and the valve positions of the expansion valves.