Check, by observing the gauge in the driver's cab, that the compressor cuts in and out at the correct pressures, and if necessary, adjust as follows:-
The unloader cut-out pressure, 95 psi, is adjusted by slackening of the locknut and turning the adjusting thimble clockwise to increase and anti-clockwise to decrease the pressure. When increasing the pressure it is desirable to screw down the thimble just beyond the desired point and then turn it back, so avoiding any twisting of the spring that will affect the setting. Tighten the locknut and recheck the setting.
There is no adjustment for the cut-in pressure (75 - 80 psi), and if this is low, it should be repaired.
With the compressor charging, check at the exhaust port for piston valve leakage, and with the compressor at rest, check for valve leakage; if leakage is detected it should be repaired.
The intake filter should be cleaned by unscrewing its cap and washing the element in paraffin.