Troubleshooting
3A6400A 29
Engine operates, but displacement
pump does not operate
Error code displayed. See LED Display Messages, page 38.
Pump switch is OFF. Turn pump switch ON.
Pressure setting too low. Turn pressure adjusting knob clockwise to
increase pressure.
Fluid filter is dirty. Clean filter.
Tip or tip filter is clogged. Clean tip or tip filter (see gun manual).
Displacement pump piston rod is stuck
due to dried paint.
Repair pump (see pump manual).
Connecting rod is worn or damaged. See Parts manual.
Drive housing is worn or damaged. See Parts manual.
Electrical power is not energizing
clutch field.
See Parts manual.
See LED Display Messages, page 38.
With pump switch ON and pressure turned to
MAXIMUM, use a test light to check for power
between clutch test points on control board.
Remove clutch wires from control board and
measure resistance across clutch coil. At 70°
F, the resistance must be between for 3900 -
1.2 + 0.2 Ω, for 5900/7900 1.7 ± 0.2 Ω; if not,
replace pinion housing.
Have pressure control checked by authorized
Graco dealer.
Clutch is worn, damaged, or incorrectly
positioned.
Adjust or replace clutch. See page 39.
Pinion assembly is worn or damaged. Repair or replace pinion assembly. Page 39.
Pump output is low Strainer is clogged. Clean strainer.
Piston ball is not seating. Service piston ball (see pump manual).
Piston packings are worn or damaged. Replace packings (see pump manual).
O-ring in pump is worn or damaged. Replace o-ring (see pump manual).
Intake valve ball is not seating
properly.
Clean intake valve (see pump manual).
Intake valve ball is packed with
material.
Clean intake valve (see pump manual).
Engine speed is too low. Increase throttle setting (see operation
manual).
Clutch is worn or damaged. Adjust or replace clutch. Page 39.
Pressure setting is too low. Increase pressure (see operation manual).
Fluid filter, tip filter or tip is clogged or
dirty.
Clean filter (see gun manual).
Large pressure drop in hose with
heavy materials.
Use larger diameter hose and/or reduce
overall length of hose. Use of more than 100 ft
of 1/4 in. hose significantly reduces
performance of sprayer. Use 3/8 in. hose for
optimum performance (50 ft minimum).
Problem Cause Solution
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