An HVAC system includes a pressure sensor is disposed in a suction line between a compressor and an indoor heat-exchange coil. The pressure sensor is electrically coupled to a compressor controller. An HVAC controller is electrically coupled to the compressor controller. The HVAC controller is configured to transmit a signal to the compressor controller to activate and de-activate the compressor. The compressor controller is configured to receive a signal from the HVAC controller to activate the compressor, determine a start speed of the compressor, monitor a run time of the compressor, and modulate a speed of the compressor.

A low ambient cooling system for a variable refrigerant flow heat pump includes an outdoor air conditioning unit and an indoor air conditioning unit. The outdoor air conditioning unit includes an outdoor heat exchanger with one or more valves that selectively control refrigerant flow through different sections of condenser coils during a low ambient cooling mode. During the low ambient cooling mode, the condenser coils of the outdoor heat exchanger include an active coil section through which refrigerant flows and an inactive coil section that is closed. An outdoor-coil restrictor plate with holes is attached to the active condenser coil in the outdoor air conditioning unit. The outdoor-coil restrictor plate restricts excessive heat release from the active coil section of the condenser coils in the outdoor heat exchanger during the low ambient cooling mode.

An HVAC system includes an outdoor heat exchanger. A first indoor heat exchanger is fluidly coupled to the outdoor heat exchanger and disposed in a first zone. A second indoor heat exchanger is fluidly coupled to the outdoor heat exchanger and disposed in a second zone. A compressor is fluidly coupled to the outdoor heat exchanger, the first indoor heat exchanger, and the second indoor heat exchanger. A first circulation fan is positioned to circulate air around the first indoor heat exchanger and a second circulation fan is positioned to circulate air around the second indoor heat exchanger. A first zone controller is electrically coupled to the first indoor heat exchanger. The first zone controller is configured to measure a temperature in the first zone, compare the measured temperature to a setpoint temperature of the first zone, and responsive to a difference between the measured temperature and the setpoint temperature, adjust a speed of the first circulation fan independent of the speed of the second circulation fan.

A usage-side air-conditioning apparatus has: a casing; a usage-side heat exchanger to cool or heat air inside the casing through the use of a refrigerant supplied from a heat-source-side air-conditioning apparatus; an air supply/exhaust mechanism to take room air and/or outdoor air in from an air-conditioned space or outside of the air-conditioned space, supply the air as supply air to the air-conditioned space, and exhaust the air as exhaust air out of the air-conditioned space; and a refrigerant leakage detection device to detect the refrigerant. When the refrigerant leakage detection device has detected the refrigerant, a refrigerant exhaust operation is performed by the air supply/exhaust mechanism to exhaust the refrigerant out of the air-conditioned space along with the air inside the casing.

Provided is a system for air-conditioning and hot-water supply configured to selectively perform cooling and heating operations, comprising: an outdoor unit having a compressor and an outdoor heat exchanger; at least one or more indoor units each of which is connected to the outdoor unit and includes an indoor heat exchanger; a hot-water supply unit connected to the outdoor unit so as to be arranged in parallel to the indoor unit and including a refrigerant-water heat exchanger; a controller configured to monitor for a request for hot-water supply from the hot-water supply unit while a cooling operation is being performed in at least one of the indoor units, and then to start the heating operation in accordance with the request; wherein the controller transmits to all of the indoor units, which are turned on for said cooling operation, a fan-stop command to stop a fan arranged at each indoor unit.

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_AVGthe set threshold Pd.sub.threshold; if Pd_AVGPd.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. Hence, according to the oil return control disclosed by this embodiment, if it requires improving oil return performance, the multi-split air conditioner working in heating mode is only being switched to cooling mode if Pd_AVG<Pd.sub.threshold and the fan within those power-on indoor units is being shut off to minimize the fluctuation of room temperature; the heating mode operation could be maintained if Pd_AVGPd.sub.threshold, oil return requirement and heating requirement could be satisfied at the same time to avoid affecting normal air conditioning operation significantly so as to solve the problem in the prior art.

Provided is an air conditioner configured such that the inside of an indoor unit is dried while an increase in a humidity in a room is suppressed. The air conditioner of the present invention includes an outdoor unit and an indoor unit having an indoor heat exchanger and a decompression device. The indoor heat exchanger has a first heat exchange portion and a second heat exchange portion. The decompression device is connected to the first heat exchange portion and the second heat exchange portion. This air conditioner performs cooling operation or dehumidifying operation in which the first heat exchange portion and the second heat exchange portion function as evaporators and reheat dehumidifying operation in which the first heat exchange portion functions as a condenser and the second heat exchange portion functions as the evaporator. Moreover, water repelling treatment is performed for the second heat exchange portion

Provided is a failure diagnosis system that diagnoses the state of an air-conditioning apparatus having a refrigerant circuit in which refrigerant circulates. The failure diagnosis system has an abnormality diagnosis unit that performs normal-operation abnormality diagnosis for determining whether or not there is an abnormality in the air-conditioning apparatus by using state data and control data during normal operation of the air-conditioning apparatus. If the abnormality diagnosis unit determines that there is an abnormality in the air-conditioning apparatus, the abnormality diagnosis unit changes a control value for an actuator of the air-conditioning apparatus and acquires state data and control data. Then, the abnormality diagnosis unit performs abnormality-cause identification diagnosis for identifying the cause of the abnormality in the air-conditioning apparatus by using the state data and the control data acquired before the change of the control value and the state data and the control data acquired after the change of the control value.

An HVAC system includes a pressure sensor is disposed in a suction line between a compressor and an indoor heat-exchange coil. The pressure sensor is electrically coupled to a compressor controller. An HVAC controller is electrically coupled to the compressor controller. The HVAC controller is configured to transmit a signal to the compressor controller to activate and de-activate the compressor. The compressor controller is configured to receive a signal from the HVAC controller to activate the compressor, determine a start speed of the compressor, monitor a run time of the compressor, and modulate a speed of the compressor.

A device and method are provided to allow replacement of costlier motors with a retrofittable control board and a lower cost motors operating a several speeds to provide variable (but not continuously variable) blower airflow. The control signals normally used to command the motor being replaced are only used to detect the need to activate the blower motor; once detected, the control board activates the replacement blower motor by energizing a blower motor speed tap with the evaporator blower initially set to a high speed. Then the blower speed is lowered if a predetermined negligibly small, acceptable change in evaporator temperature has occurred. Given the number of speed taps on the replacement blower motor, the evaporator blower speed is continued to be reduced from the initially set high speed as long as there is only an acceptably small change in the measured evaporator temperature.