HVAC systems and controls

1. A method of controlling a HVAC system, comprising:

obtaining an unloader state of an unloader of a compressor of the HVAC system, the unloader being a device located between an inlet and an outlet of the compressor and configured to control a gas flow through the compressor;

obtaining a control parameter based on the unloader state; and

controlling the HVAC system based on the control parameter,

wherein obtaining the unloader state of the compressor of the HVAC system includes:

obtaining a compressor operation condition;

obtaining a measurable parameter of the compressor; and

estimating the unloader state based on an association between the unloader state and the measurable parameter of the compressor according to the obtained compressor operation condition, the association between the unloader state and the measurable parameter of the compressor is represented by a first curve,

wherein obtaining the control parameter based on the unloader state is based on an association between the estimated unloader state and the control parameter according to the obtained compressor operation condition, and the association between the estimated unloader state and the control parameter is represented by a second curve.

2. The method of claim 1 , wherein controlling the HVAC system includes, controlling a fan operation speed, an operation of a compressor, an orifice size of an expansion device, or a combination thereof.

3. The method of claim 1 , wherein the compressor operation condition includes a saturated suction temperature at an inlet of the compressor, a saturated discharged temperature at an outlet of the compressor, or a combination thereof.

4. The method of claim 1 , wherein the measurable parameter of the compressor includes a current draw by the compressor, a torque of the compressor, a power of the compressor, or a combination thereof.

5. The method of claim 1 , wherein the control parameter is an actual mass flow rate, a rated mass flow rate, or a combination thereof.

6. The method of claim 1 , further comprising:

controlling the unloader state to adjust to a target unloader state;

obtaining a second unloader state after the adjustment;

comparing the second unloader state to the target unloader state; and

providing an error message when the second unloader state is different from the target unloader state.

7. The method of claim 1 , wherein the first curve is estimated by a first operation function having multiple coefficient polynominals, and the second curve is estimated by a second operation function having multiple coefficient polynominals.