True/False Indicate whether the statement is true or false. 11. Electronic leak detectors can only be used to detect CFCs. 12. Disposable cylinders are designed to be used for refrigerant recovery. 13. Refrigerant must be recovered from a leaking system before repairs can be performed. 14. A gauge that reads absolute pressure should be adjusted depending on the elevation. 15. The pressure of a perfect vacuum is 29.92 in. Hg. 16. Both valves need to be closed on a gauge manifold in order to evacuate a system. 17. A decrease in temperature can cause the pressure in a cylinder to increase. 18. Service valves are front seated for normal system operation. 19. The compound gauge measures pressure both above and below atmospheric pressure. 20. Fluorescent leak detectors require the use of a halogen light.