Atlas Copco QAS 38 troubleshooting: 70 symptom-cause-remedy entries from the manufacturer's own service documentation.
Atlas Copco QAS 38 — full specs, parts & maintenance.
| Symptom | Cause | Remedy |
|---|---|---|
| The starter motor turns the engine too slowly | Battery capacity too low | |
| The starter motor turns the engine too slowly | Bad electrical connection | |
| The starter motor turns the engine too slowly | Fault in starter motor | |
| The starter motor turns the engine too slowly | Wrong grade of lubricating oil | |
| The engine does not start or is difficult to start | Starter motor turns engine too slowly | |
| The engine does not start or is difficult to start | Fuel tank empty | |
| The engine does not start or is difficult to start | Fault in fuel control solenoid | |
| The engine does not start or is difficult to start | Restriction in a fuel pipe | |
| The engine does not start or is difficult to start | Fault in fuel lift pump | |
| The engine does not start or is difficult to start | Dirty fuel filter element | |
| The engine does not start or is difficult to start | Air in fuel system | |
| The engine does not start or is difficult to start | Fault in atomisers | |
| The engine does not start or is difficult to start | Cold start system used incorrectly | |
| The engine does not start or is difficult to start | Fault in cold start system | |
| The engine does not start or is difficult to start | Restriction in fuel tank vent | |
| The engine does not start or is difficult to start | Wrong type or grade of fuel used | |
| The engine does not start or is difficult to start | Restriction in exhaust pipe | |
| Not enough power | Restriction in a fuel pipe | |
| Not enough power | Fault in fuel lift pump | |
| Not enough power | Dirty fuel filter element | |
| Not enough power | Restriction in air filter/cleaner or induction system | |
| Not enough power | Air in fuel system | |
| Not enough power | Fault in atomisers or atomisers of an incorrect type | |
| Not enough power | Restriction in fuel tank vent | |
| Not enough power | Wrong type or grade of fuel used | |
| Not enough power | Restricted movement of engine speed control | |
| Not enough power | Restriction in exhaust pipe | |
| Not enough power | Engine temperature is too high | |
| Not enough power | Engine temperature is too low | |
| Misfire | Restriction in a fuel pipe | |
| Misfire | Fault in fuel lift pump | |
| Misfire | Dirty fuel filter element | |
| Misfire | Air in fuel system | |
| Misfire | Fault in atomisers or atomisers of an incorrect type | |
| Misfire | Fault in cold start system | |
| Misfire | Engine temperature is too high | |
| Misfire | Incorrect valve tip clearances | |
| The pressure of the lubricating oil is too low | Wrong grade of lubricating oil | |
| The pressure of the lubricating oil is too low | Not enough lubricating oil in sump | |
| The pressure of the lubricating oil is too low | Defective gauge | |
| The pressure of the lubricating oil is too low | Dirty lubricating oil filter element | |
| High fuel consumption | Restriction in air filter/cleaner or induction system | |
| High fuel consumption | Fault in atomisers or atomisers of an incorrect type | |
| High fuel consumption | Fault in cold start system | |
| High fuel consumption | Wrong type or grade of fuel used | |
| High fuel consumption | Restricted movement of engine speed control | |
| High fuel consumption | Restriction in exhaust pipe | |
| High fuel consumption | Engine temperature is too low | |
| High fuel consumption | Incorrect valve tip clearances | |
| Black exhaust smoke | Restriction in air filter/cleaner or induction system | |
| Black exhaust smoke | Fault in atomisers or atomisers of an incorrect type | |
| Black exhaust smoke | Fault in cold start system | |
| Alternator does not excite. | Blown fuse. | Replace fuse. |
| Alternator does not excite. | Insufficient residual voltage. | Increase the speed by 15 %. |
| Alternator does not excite. | No residual voltage. | For an instant apply on the + and – terminals of the electronic regulator a 12 V battery voltage with a 30 Ω resistor in series respecting the polarities. |
| After being excited alternator does not excite. | Connections are interrupted. | Check connection cables as per attached drawings. |
| Low voltage at no load. | Voltage potentiometer out of setting. | Reset voltage. |
| Low voltage at no load. | Intervention of protection. | Check rpm. |
| Low voltage at no load. | Winding failure. | Check windings. |
| High voltage at no load. | Voltage potentiometer out of setting. | Reset voltage. |
| High voltage at no load. | Failed regulator. | Substitute regulator. |
| Lower than rated voltage at load. | Voltage potentiometer out of setting. | Reset voltage potentiometer. |
| Lower than rated voltage at load. | Intervention by protection. | Current too high, power factor lower than 0.8; speed lower than 10 % of rated speed. |
| Lower than rated voltage at load. | Failed regulator. | Substitute regulator. |
| Lower than rated voltage at load. | Rotating bridge failure. | Check diodes, disconnect cables. |
| Higher than rated voltage at load. | Voltage potentiometer out of setting. | Reset voltage potentiometer. |
| Higher than rated voltage at load. | Loose sensing wires on AVR. | Check sensing wires on AVR. |
| Higher than rated voltage at load. | Failed regulator. | Substitute regulator. |
| Unstable voltage. | Speed variation in engine. | Check regularity of rotation. |
| Unstable voltage. | Regulator out of setting. | Regulate stability of regulator by acting on “STABILITY” potentiometer. |
Fault codes and symptom→remedy steps extracted from this model’s service/owner documentation; verify against the official manual before servicing.
Documented causes: Starter motor turns engine too slowly; Fuel tank empty; Fault in fuel control solenoid; Restriction in a fuel pipe. See the table for the matching fixes.
Documented causes: Restriction in a fuel pipe; Fault in fuel lift pump; Dirty fuel filter element; Restriction in air filter/cleaner or induction system. See the table for the matching fixes.
Documented causes: Restriction in a fuel pipe; Fault in fuel lift pump; Dirty fuel filter element; Air in fuel system. See the table for the matching fixes.