Method and system for defrosting a heat exchanger

1. A method for defrosting a heat exchanger of a refrigeration circuit, the method comprising:

monitoring a compressor suction parameter at a suction line to a compressor of the refrigeration circuit;

monitoring an ambient temperature of ambient air outside of a conditioned space;

determining a compressor suction parameter threshold based on the ambient temperature, wherein the compressor suction parameter threshold is a variable threshold value; and

initiating a defrost mode of the refrigeration circuit when the compressor suction parameter monitored at the suction line of the compressor is less than or equal to the compressor suction parameter threshold that is a variable threshold value determined based on the ambient temperature.

2. The method of claim 1 , wherein the compressor suction parameter is a compressor suction pressure.

3. The method of claim 1 , wherein the compressor suction parameter is a compressor suction temperature.

4. The method of claim 1 , further comprising:

monitoring a temperature at an outlet of the heat exchanger of the refrigeration circuit;

terminating the defrost mode when the temperature at the outlet of the heat exchanger is equal to or greater than a temperature threshold.

5. A system for conditioning air within a conditioned space, the system comprising:

a refrigeration circuit that includes a compressor and an outside heat exchanger;

an ambient temperature sensor configured to monitor an ambient temperature of ambient air outside of the conditioned space;

a compressor suction parameter sensor configured to monitor a compressor suction parameter at a suction line to the compressor; and

a controller configured to receive compressor suction parameter data from the compressor suction parameter sensor, configured to receive ambient temperature data from the ambient temperature sensor, configured to determine a compressor suction parameter threshold based on the ambient temperature data, wherein the compressor suction parameter threshold is a variable threshold value, and configured to initiate a defrost mode when the compressor suction parameter monitored at the suction line of the compressor is less than or equal to the compressor suction parameter threshold that is a variable threshold value determined based on the ambient temperature.

6. The system of claim 5 , wherein the compressor suction parameter is a compressor suction pressure.

7. The system of claim 5 , wherein the compressor suction parameter is a compressor suction temperature.

8. The system of claim 5 , further comprising:

a temperature sensor configured to monitor a temperature at an outlet of the outside heat exchanger;

wherein the controller is configured to terminate the defrost mode when the temperature at the outlet of the outside heat exchanger is equal to or greater than a temperature threshold.

9. A vehicle comprising:

a frame enclosing a conditioned space; and

a heating, ventilation and air conditioning (HVAC) unit coupled to the frame and configured to condition air within the conditioned space, the HVAC unit including:

a refrigeration circuit that includes a compressor and an outside heat exchanger,

an ambient temperature sensor configured to monitor an ambient temperature of ambient air outside of the conditioned space,

a compressor suction parameter sensor configured to monitor a compressor suction parameter at a suction line to the compressor, and

a controller configured to receive compressor suction parameter data from the compressor suction parameter sensor, configured to receive ambient temperature data from the ambient temperature sensor, configured to determine a compressor suction parameter threshold based on the ambient temperature data, wherein the compressor suction parameter threshold is a variable threshold value, and configured to initiate a defrost mode when the compressor suction parameter monitored at the suction line of the compressor is less than or equal to the compressor suction parameter threshold that is a variable threshold value determined based on the ambient temperature.

10. The vehicle unit of claim 9 , wherein the compressor suction parameter is a compressor suction pressure.

11. The vehicle of claim 9 , wherein the compressor suction parameter is a compressor suction temperature.

12. The vehicle of claim 9 , wherein the HVAC unit includes a temperature sensor configured to monitor a temperature at an outlet of the outside heat exchanger; and

wherein the controller is configured to terminate the defrost mode when the temperature at the outlet of the outside heat exchanger is equal to or greater than a temperature threshold.

13. The method of claim 1 , wherein determining the compressor suction parameter threshold based on the ambient temperature includes using a lookup table of previous test results indicating the compressor suction parameter threshold of the refrigeration circuit at different ambient temperatures.

14. The system of claim 5 , wherein the controller is configured to configured to determine the compressor suction parameter threshold based on the ambient temperature data by using a lookup table of previous test results indicating the compressor suction parameter threshold of the refrigeration circuit at different ambient temperatures.

15. The vehicle of claim 9 , wherein the controller is configured to configured to determine the compressor suction parameter threshold based on the ambient temperature data by using a lookup table of previous test results indicating the compressor suction parameter threshold of the refrigeration circuit at different ambient temperatures.

16. The method of claim 1 , wherein the refrigeration circuit provides heat exchange between the ambient air and air in the conditioned space.