Esab PCM875 low air pressure warning

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I have an Esab PCM 875 Plasma cutter that is not working and is giving a low air pressure warning.  we have 90 psi on the gauge.  is there a pressure sensor I can check?  Has any one experienced this problem and can give a good diagnostic procedure?  i don't want to just start replacing sensors and circuit boards.  We are car guys and diagnose fuel injection systems.  Any suggestions and/or advice is appreciated.PeterPeterDMotorsports.com
Reply:Usually the problem is not the pressure sensor...rather, the sensor is doing its job letting you know there is a low pressure problem. Usually..the pressure switch or transducer is internal in the plasma...located between the inlet gas (after the filter bowl/regulator) and before the solenoid valve and torch leads.- Low pressure (most often) is a partially plugged inlet fitting, too small of an inlet hose (should be a miniumum of 3/8" ID) or a plugged/clogged/saturated filter element.-Low pressure can also indicate a leak at the torch....in the torch leads...or in the internal plasma syustem plumbing. Look for a leaking or missing oring...incorrect consumables, loose fitting in the torch or on the power supply end, or a split hose.Your inlet pressure should be somewhere between 90 and 140 psi. If you keep it set at 90.....activating the plasma air flow may be enough flow to cause the pressure to drop. On many plasma systems...the internal pressure sensor is set to drop out at 85 psi.Jim Colt    Hypertherm