System and method for controlling an economizer circuit

1. A method of controlling a circuit in a vapor compression system, the circuit comprising a tank, a first line connecting the tank and a first heat exchanger, a second line connecting the tank and a second heat exchanger, a third line connecting the tank and a port in a compressor of the vapor compression system, and a valve configured and positioned in the third line to regulate fluid flow in the third line, the method comprising:

measuring a level of liquid in the tank;

comparing the measured level of liquid to a predetermined liquid level;

measuring an operating parameter of the compressor;

comparing the measured operating parameter to a first predetermined value related to the operating parameter;

opening the valve in response to the measured level of liquid being less than the predetermined liquid level and the measured operating parameter being greater than the first predetermined value;

comparing the measured operating parameter to a second predetermined value related to the operating parameter; and

closing the valve in response to the measured operating parameter being less than the second predetermined value.

2. The method of claim 1 wherein the first predetermined value is a first predetermined output frequency from a variable speed drive and the second predetermined value is a second predetermined output frequency from a variable speed drive.

3. The method of claim 1 further comprising:

determining whether the compressor is operating; and

closing the valve in response to a determination that the compressor is not operating.

4. The method of claim 1 further comprising:

measuring an outdoor temperature;

comparing the measured outdoor temperature to a predetermined temperature;

calculating an operating time for the compressor;

comparing the calculated operating time to a predetermined time period; and

opening the valve in response to the measured level of liquid being less than the predetermined liquid level and the measured outdoor temperature being less than the predetermined temperature and the calculated operating time being less than the predetermined time period.

5. The method of claim 4 further comprising:

measuring a temperature of a motor used with the compressor;

comparing the measured motor temperature to a predetermined motor temperature;

determining whether a timer associated with the valve has completed; and

opening the valve in response to the measured level of liquid being less than the predetermined liquid level and the measured outdoor temperature being less than the predetermined temperature and the calculated operating time being less than the predetermined time period and the measured motor temperature being less than the predetermined motor temperature and a determination that the timer has completed.

6. The method of claim 1 further comprising determining whether the valve is open.

7. The method of claim 6 further comprising:

comparing the measured operating parameter of the compressor to a second predetermined value related to the operating parameter;

measuring a temperature of a motor used with the compressor;

comparing the measured motor temperature to a predetermined temperature; and

closing the valve in response to a determination that the measured operating parameter is less than the second predetermined value or the measured motor temperature is greater than the predetermined temperature.

8. The method of claim 1 further comprising:

measuring a temperature of a motor used with the compressor;

comparing the measured motor temperature to a predetermined temperature;

determining whether a timer associated with the valve has completed; and

opening the valve in response to the measured liquid level being less than the predetermined liquid level and the measured operating parameter being greater than the first predetermined value and the measured motor temperature being less than the predetermined temperature and a determination that the timer has completed.

9. A method of controlling fluid through a tank in a vapor compression system comprising:

providing a valve in a line connecting an outlet of the tank and a compressor of the vapor compression system, the valve being configured and positioned to regulate fluid flow through the tank;

measuring an outdoor temperature;

comparing the measured outdoor temperature to a predetermined temperature;

calculating an operating time for the compressor;

comparing the calculated operating time to a predetermined time period;

measuring a fluid level in the tank;

comparing the measured fluid level to a predetermined level; and

opening the valve in response to the measured fluid level being less than the predetermined level and the outdoor temperature being less than a predetermined temperature and the calculated operating time being less than a predetermined time period.

10. The method of claim 9 further comprising:

determining whether a timer associated with the valve has completed;

measuring a temperature of the motor;

comparing the measured temperature to a predetermined temperature; and

opening the valve in response to the measured fluid level being less than the predetermined level and the outdoor temperature being less than a predetermined temperature and the calculated operating time being less than a predetermined time period and the measured motor temperature being less than the predetermined temperature and the determination that the timer has completed.

11. The method of claim 9 further comprising determining whether the valve is open.

12. The method of claim 11 further comprising:

measuring a temperature of the motor;

comparing the measured temperature to a predetermined temperature; and

measuring an operating parameter of the compressor;

comparing the measured operating parameter to a predetermined value related to the operating parameter; and

closing the valve in response to a determination that the valve is open and the measured operating parameter being less than the predetermined value related to the operating parameter or the measured motor temperature being greater than the predetermined temperature.

13. The method of claim 12 further comprising:

comparing the measured operating parameter to a second predetermined value related to the operating parameter;

closing the valve in response to a determination that the valve is open and the measured operating parameter is less than the second predetermined value related to the operating parameter.

14. The method of claim 13 further comprising:

determining whether a timer associated with the value has completed; and

closing the valve in response to a determination that the valve is open and the measured operating parameter is less than the operating parameter or a determination that the timer has completed.

15. The method of claim 9 further comprising:

determining whether the compressor is operating; and

closing the valve in response to a determination that the compressor is not operating.

16. A circuit for a vapor compression system, the circuit comprising:

a tank, a first line connecting the tank and a first heat exchanger;

a second line connecting the tank and a second heat exchanger;

a third line connecting the tank and a port in a compressor of the vapor compression system;

a valve configured and positioned in the third line to regulate fluid flow in the third line;

a microprocessor being configured to open the valve in response to a fluid level in the tank being less than a predetermined level and an operating parameter of a compressor being greater than a first predetermined value related to the operating parameter; and

the microprocessor being configured to open the valve to in response to a fluid level in the tank being less than a predetermined level, an outdoor temperature being less than a predetermined temperature and an operating time of the compressor being less than a predetermined time value.

17. The circuit of claim 16 wherein the valve is a solenoid valve.