ASE Study Guide 2026

CNG systems store gas at extremely high pressure (3,600 PSI). Before any fuel system work, the manual shutoff valves on each cylinder must be closed to isolate the high-pressure supply. Residual pressure in the lines must be safely relieved following OEM procedures. Pressure must be verified at zero using an appropriate gauge before opening any fitting. Failure to properly depressurize can result in explosive fuel release and fire or asphyxiation.

Contaminated refrigerant must be stored separately in a dedicated cylinder labeled for contaminated refrigerant and sent to a certified reclaimer; venting is never permitted.

A broken compressor reed valve typically results in reduced compression efficiency. This would lead to lower-than-normal high-side pressure and higher-than-normal low-side pressure, or even equalization of pressures, as the compressor cannot effectively move refrigerant. It would not cause the high-side pressure to exceed specifications; instead, it would cause a loss of cooling performance due to insufficient pressure differential.

California (CARB) emissions vehicles often require different parts than federal-spec ones.

A condition affecting all cylinders, such as a vacuum leak or low fuel pressure, causes random misfires with lean trims.

The manual valve is moved by the shift linkage to route fluid according to the selected gear range.