Alternator & Regulator: Diagnosis GMC Pickup C2500

TROUBLE SHOOTING

Note. See TROUBLE SHOOTING - BASIC PROCEDURES article in the GENERAL TROUBLE SHOOTING section.

ON-VEHICLE TESTING

Note. Before making electrical checks, visually inspect all terminals for clean, tight connections. Check alternator mounting bolts and drive belt tension. Ensure battery is in good condition prior to testing charging system.

Alternator Output Test

1. Connect an ammeter in series with wire connected to BAT terminal of alternator. see scheme 2 Turn on all available accessories. Connect a carbon pile across battery. Operate engine at 2000 RPM. Adjust carbon pile (as required) to obtain maximum current output while maintaining 13 volts or more.
2. Ampere output must be within 15 amps of rated output. If output is not within 15 amps of rated output, replace alternator. See «ALTERNATOR IDENTIFICATION & OUTPUT»(ref-58361-S35443199002001011700000).

BENCH TESTING

Note. Internal components of CS130 alternator are not serviceable. Alternator replacement is required.

Scheme 3

1. To check for ground, attach one ohmmeter lead to shaft and other lead to either slip ring. (Scheme 3) If reading is not infinity, replace rotor.
2. To test for open, attach one ohmmeter lead to each slip ring. (Scheme 3) Resistance should be low. If reading is high (infinity), replace rotor.
3. To test for short, connect battery and ammeter in series with edge of two slip rings. Reading should be 124 amps. If reading is greater than 124 amps, winding is shorted, replace rotor.
4. To test for excessive resistance, connect ohmmeter across 2 slip rings. Reading should be 2.1-2.4 ohms at 80°F (27°C). If reading is greater than 2.4 ohms, excessive resistance is present. If reading is less than 2.1 ohms, winding is shorted, replace rotor.
5. Resistance and ammeter readings will vary slightly with winding temperature changes. If alternator does not supply rated output, and rotor is okay, rectifier bridge, stator or regulator is faulty.

Stator Test (CS144)

1. To check for ground, connect one ohmmeter lead to any stator lead. Connect remaining ohmmeter lead to stator frame. Ohmmeter reading should be infinity. (Scheme 4)
2. Delco CS series alternators have delta stator windings and cannot be tested for short or open circuits with ohmmeter. A noticeable discoloration anywhere on the stator usually indicates stator failure.

Scheme 4

Note. Some digital ohmmeters cannot be used to check diodes in rectifier bridge. Consult ohmmeter manufacturer to determine ohmmeter capabilities.

Scheme 5

1. Position ohmmeter with one lead touching grounded heat sink and other lead pressed firmly against flat metal clip on one of 3 terminals. Observe reading, and reverse test lead connections. (Scheme 5)
2. If readings are same, replace rectifier bridge. A good bridge will give a high and low reading. Repeat tests for remaining terminals. There should be 6 tests altogether (2 tests at each terminal).
3. Connect test leads to insulated heat sink and one of the 3 terminals. (Scheme 5) Observe reading and reverse connections. Repeat tests for remaining terminals. There should be a total of 6 tests (2 at each terminal).
4. Testing is complete when all 12 tests have been made. If any terminals have same readings for both connections (leads reversed), replace rectifier bridge.

Regulator Test (CS144)

Regulator cannot be tested for short, open or grounded circuits. If rotor, stator and rectifier bridge are okay and alternator continues to produce greater than 16 volts or does not produce within 15 amps of rated output during alternator output test, replace regulator. See ALTERNATOR IDENTIFICATION & OUTPUT .

Inspection

1. Using clean solvent, wash all metal parts except voltage regulator, rectifier bridge, bearings, stator and rotor. Inspect terminal connections for corrosion and damage. Inspect alternator housing for cracks, warping and damage. Replace alternator as necessary.
2. Inspect stator windings and rotor for burned (blackened) insulation. Replace stator or rotor as necessary. Inspect stator windings for chipped insulation. Repair with insulating varnish or replace stator if damage is excessive.
3. Inspect rotor slip rings. They may be cleaned with 400 grit or finer polishing cloth while rotor is being rotated. Slip rings may be lathe turned to maximum indicator reading of .002" (.05 mm). Slip rings are not replaceable. Replace rotor if slip rings are excessively damaged. Inspect slip ring end of rotor shaft for overheating or scoring. Replace rotor as necessary.
4. Inspect front bearing for looseness, roughness and wear. Replace as necessary. Rear bearing must be replaced if alternator is disassembled.
5. Inspect brushes for wear. Replace if worn to less than 50 percent of original length. Inspect brush holder for damage. Inspect brush springs for corrosion or damage.