What is Kobelco SK135SR-2 Fault Code B064?

Kobelco SK135SR-2 Fault Code B064 indicates a malfunction in the air conditioning (A/C) compressor circuit within the excavator's electrical system. This diagnostic trouble code (DTC) is triggered when the Electronic Control Module (ECM) detects an abnormal electrical signal—either an open circuit, short circuit, or improper voltage—in the wiring or components controlling the A/C compressor clutch relay.

While this may seem like a comfort issue rather than a critical operational fault, ignoring B064 can lead to electrical system complications. In used excavators, degraded wiring can cause voltage irregularities that affect other cab electrical components. The A/C system relies on precise 12-volt DC signals to engage the compressor clutch through a relay controlled by the cab climate control panel and monitored by the ECM.

Common Symptoms

When Code B064 is active on your SK135SR-2, operators typically experience:

• A/C system completely inoperative despite climate control settings being activated
• Warning indicator light illuminated on the instrument cluster (typically an A/C or electrical system warning)
• Intermittent A/C function where the compressor engages and disengages randomly during operation
• No abnormal engine performance issues, as this code does not affect hydraulic or powertrain systems
• Potential electrical smell or heat near the cab fuse panel in severe short-circuit situations

Potential Causes

The most common technical failures triggering B064 in used Kobelco SK135SR-2 excavators include:

• Faulty A/C compressor clutch relay (located in the cab's main relay panel)—relay contacts wear over time causing intermittent connections
• Damaged wiring harness between the climate control panel and compressor clutch, especially at harness routing points near the cab door hinge where flexing causes wire fatigue
• Corroded electrical connectors at the compressor clutch coil connection point on the engine-mounted A/C compressor
• Failed A/C compressor clutch coil, which can develop internal short circuits or open windings (typically measures 3-5 ohms when functional)
• ECM software glitch or corrupted fault code memory requiring system reset

How to Troubleshoot and Fix Code B064

Step 1: Initial Electrical System Inspection Using a digital multimeter (DMM), verify battery voltage is within 12-14.5 volts with the engine running. Check all main fuses and the specific A/C system relay in the cab fuse/relay panel. Look for signs of overheating, corrosion, or damaged relay terminals—common in machines with 3,000+ operating hours.

Step 2: Test the A/C Compressor Clutch Coil Disconnect the electrical connector at the A/C compressor (mounted on the engine). Using your multimeter set to ohms, measure resistance across the clutch coil terminals. A functioning coil should read 3-5 ohms. An open circuit (infinite resistance) or near-zero resistance indicates clutch coil failure requiring compressor replacement or clutch assembly rebuild.

Step 3: Inspect Wiring Harness and Connectors Trace the wiring harness from the cab climate control panel to the relay panel, then to the compressor clutch. On used excavators, pay special attention to harness routing near the cab door and along the engine compartment firewall where vibration and heat cause insulation breakdown. Look for chafed wires, exposed copper, or green corrosion at connector pins.

Step 4: Test and Replace the A/C Relay With the ignition on (engine off), activate the A/C system. You should hear an audible click from the relay. If absent, remove the relay and bench-test it by applying 12 volts to the coil terminals while checking continuity across the switched terminals. Replace with genuine Kobelco relay (part number specific to SK135SR-2) if faulty.

Step 5: Clear Codes and Verify Repair After repairs, use Kobelco diagnostic software (DYNA MAXX or compatible scan tool) to clear stored fault codes from ECM memory. Operate the A/C system for 15-20 minutes under various conditions to ensure B064 does not return. Monitor voltage at the compressor clutch during engagement—should read battery voltage when activated.

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Disclaimer: This guide provides general diagnostic procedures for Code B064. Always consult the Kobelco SK135SR-2 service manual for model-specific specifications. If unfamiliar with electrical diagnostics, contact a certified Kobelco technician to prevent further electrical system damage.