Leaking pressure 5 ton wrecker

The air system works, then not, then works, then not...etc, etc... When it works, air pressure is 115-120. When not, it struggles between 60 & 90 with the alarm on the entire time. Without proper air pressure, the winches and crane are useless extra weight.

The wrecker is 1990 M936A2. Thanks for the help.

Have you serviced the air dryer ?
Also check the air governor and unloader valve.

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