Cooling system

1. An apparatus comprising:

a high side heat exchanger configured to remove heat from a refrigerant;

a flash tank configured to store the refrigerant;

a first load configured to use the refrigerant from the flash tank to cool a first space proximate the first load;

a second load;

a third load;

a first compressor; and

a second compressor;

during a first mode of operation:

the second load is configured to use the refrigerant from the flash tank to cool a second space proximate the second load;

the third load is configured to use the refrigerant from the flash tank to cool a third space proximate the third load;

the second compressor is configured to compress the refrigerant from the second load and the third load; and

the first compressor is configured to compress the refrigerant from the first load and the second compressor, and

during a second mode of operation:

the second compressor is configured to compress the refrigerant from the second load and to direct the compressed refrigerant to the third load to defrost the third load.

2. The apparatus of claim 1 , wherein, during the second mode of operation, the refrigerant at the third load condenses.

3. The apparatus of claim 2 , wherein, during the second mode of operation, the flash tank is further configured to direct a liquid portion of the refrigerant from the third load to at least one of the first load and the second load.

4. The apparatus of claim 2 , wherein, during the second mode of operation, the flash tank is further configured to direct a vapor portion of the refrigerant from the third load to the first compressor.

5. The apparatus of claim 1 , further comprising a valve configured to direct a flash gas from the flash tank to the first compressor.

6. The apparatus of claim 5 , wherein, during the second mode of operation, the refrigerant from the third load is directed through the valve before the refrigerant reaches the flash tank.

7. The apparatus of claim 1 , wherein, during the second mode of operation, the second load is further configured to use the refrigerant from the flash tank to cool the second space.

8. A method comprising:

removing, by a high side heat exchanger, heat from a refrigerant;

storing, by a flash tank, the refrigerant;

using, by a first load, the refrigerant from the flash tank to cool a first space proximate the first load;

during a first mode of operation:

using, by a second load, refrigerant from the flash tank to cool a second space proximate the second load;

using, by a third load, the refrigerant from the flash tank to cool a third space proximate the third load;

compressing, by a second compressor, the refrigerant from the second load and the third load; and

compressing, by a first compressor, the refrigerant from the first load and the second compressor, and

during a second mode of operation:

compressing, by the second compressor, the refrigerant from the second load; and

directing, by the second compressor, the compressed refrigerant to the third load to defrost the third load.

9. The method of claim 8 , wherein, during the second mode of operation, the refrigerant at the third load condenses.

10. The method of claim 9 , further comprising, during the second mode of operation, directing, by the flash tank, a liquid portion of the refrigerant from the third load to at least one of the first load and the second load.

11. The method of claim 9 , further comprising, during the second mode of operation, directing, by the flash tank, a vapor portion of the refrigerant from the third load to the first compressor.

12. The method of claim 8 , further comprising directing, by a valve, a flash gas from the flash tank to the first compressor.

13. The method of claim 12 , wherein, during the second mode of operation, the refrigerant from the third load is directed through the valve before the refrigerant reaches the flash tank.

14. The method of claim 8 , further comprising, during the second mode of operation, using, by the second load, the refrigerant from the flash tank to cool the second space.

15. A system comprising:

a flash tank configured to store a refrigerant;

a first load configured to use the refrigerant from the flash tank to cool a first space proximate the first load;

a second load;

a third load;

a first compressor; and

a second compressor;

during a first mode of operation:

the second load is configured to use the refrigerant from the flash tank to cool a second space proximate the second load;

the third load is configured to use the refrigerant from the flash tank to cool a third space proximate the third load;

the second compressor configured to compress the refrigerant from the second load and the third load; and

the first compressor configured to compress the refrigerant from the first load and the second compressor, and

during a second mode of operation:

the second compressor configured to compress the refrigerant from the second load and to direct the compressed refrigerant to the third load to defrost the third load.

16. The system of claim 15 , wherein, during the second mode of operation, the refrigerant at the third load condenses.

17. The system of claim 16 , wherein, during the second mode of operation, the flash tank is further configured to direct a liquid portion of the refrigerant from the third load to at least one of the first load and the second load.

18. The system of claim 16 , wherein, during the second mode of operation, the flash tank is further configured to direct a vapor portion of the refrigerant from the third load to the first compressor.

19. The system of claim 15 , further comprising a valve configured to direct a flash gas from the flash tank to the first compressor.

20. The system of claim 19 , wherein, during the second mode of operation, the refrigerant from the third load is directed through the valve before the refrigerant reaches the flash tank.