Defrost operations and apparatus for a transport refrigeration system

1. A method for operating a defrost mode of a transport refrigerant vapor compression system including a refrigerant circuit including, in a serial arrangement, a refrigerant compression device, a refrigerant heat rejection heat exchanger, a secondary expansion device, an economizer device, a primary expansion device, a refrigerant heat absorption heat exchanger and a suction modulation valve between the refrigerant heat absorption heat exchanger and a suction port of the refrigerant compression device, the method comprising:

closing the suction modulation valve and partially opening the primary expansion device and opening the secondary expansion device to an open position;

initiating a defrost operation for the transport refrigerant vapor compression system by energizing heaters operatively coupled to the heat absorption heat exchanger operable to defrost the heat absorption heat exchanger;

during the defrost operation, comparing a heat absorption heat exchanger pressure to a first predetermined limit, where the first predetermined limit is less than a pressure release valve prescribed pressure;

in response to the heat absorption heat exchanger pressure being less than the first predetermined limit, performing at least one operation to determine if the defrost operation should be exited; and

in response to the heat absorption heat exchanger pressure being greater than the first predetermined limit, exiting the defrost operation.

2. The method of claim 1 , wherein the at least one operation to determine if the defrost operation should be exited comprises passing of a prescribed time interval or determining that a monitored state of the heat absorption heat exchanger indicates defrost completion or detecting a malfunction.

3. The method of claim 2 , wherein the detecting a malfunction comprises monitoring pressure at a location between the primary expansion device and the suction port of the refrigerant compression device.

4. The method of claim 2 , wherein the detecting the malfunction comprises:

comparing a condition of the heat absorption heat exchanger to a threshold condition; and

interrupting the defrost operation when the condition of the heat absorption heat exchanger is above the threshold condition.

5. The method of claim 4 , wherein the condition is a pressure of refrigerant in the refrigerant heat absorption heat exchanger, and wherein the threshold condition is a refrigerant pressure value less than the pressure release valve prescribed pressure.

6. The method of claim 4 , wherein interrupting the defrost operation comprises:

energizing a heat rejection heat exchanger fan to reduce temperature;

disabling the heaters; and

performing a defrost operation status check.

7. The method of claim 6 , wherein the defrost operation status check comprises determining a temperature drop across the heat absorption heat exchanger, wherein the defrost operation status check is affirmative when the determined temperature drop across the heat absorption heat exchanger is less than a prescribed value and the defrost operation status check is negative when the determined temperature drop across the heat absorption heat exchanger is not less than the prescribed value.

8. The method of claim 7 , wherein the determined temperature drop is return air temperature minus supply air temperature of the transport refrigerant vapor compression system.

9. A method for operating a defrost mode of a transport refrigerant vapor compression system including a refrigerant circuit including, in a serial arrangement, a refrigerant compression device, a refrigerant heat rejection heat exchanger, a secondary expansion device, an economizer device, a primary expansion device, a refrigerant heat absorption heat exchanger and a suction modulation valve between the refrigerant heat absorption heat exchanger and a suction port of the refrigerant compression device, the method comprising:

entering a defrost mode;

upon entering the defrost mode, comparing a heat absorption heat exchanger pressure to a first predetermined limit, where the first predetermined limit is less than a pressure release valve prescribed pressure, wherein when the heat absorption heat exchanger pressure is greater than the first predetermined limit reducing the heat absorption heat exchanger pressure and exiting the defrost mode;

wherein when the heat absorption heat exchanger pressure is less than the first predetermined limit, closing the suction modulation valve and partially opening the primary expansion device and opening the secondary expansion device to an open position;

after closing the suction modulation valve, initiating a defrost operation for the transport refrigerant vapor compression system by energizing heaters operatively coupled to the heat absorption heat exchanger operable to defrost the heat absorption heat exchanger;

during the defrost operation, comparing the heat absorption heat exchanger pressure to the first predetermined limit;

during the defrost operation, in response to the heat absorption heat exchanger pressure being less than the first predetermined limit, performing at least one operation to determine if the defrost operation should be exited; and

during the defrost operation, in response to the heat absorption heat exchanger pressure being greater than the first predetermined limit, reducing the heat absorption heat exchanger pressure and exiting the defrost mode.