What is Kobelco SK135SRLC-2 Fault Code B064?

Fault Code B064 on the Kobelco SK135SRLC-2 indicates a malfunction in the air conditioner compressor clutch relay circuit. This code specifically points to an electrical fault within the A/C system control circuit, where the Engine Control Module (ECM) detects an abnormal voltage or current reading when attempting to engage the air conditioning compressor clutch.

In the SK135SRLC-2's electrical architecture, the ECM monitors the relay circuit that controls power delivery to the compressor clutch solenoid. When the circuit resistance falls outside manufacturer specifications (typically due to short circuits, open circuits, or relay failure), the system triggers B064 and may disable A/C operation to prevent further electrical damage. While this doesn't affect core hydraulic or engine functions, it impacts operator comfort and can indicate broader electrical system deterioration in used machines.

Common Symptoms

• A/C system completely non-functional despite climate control settings being activated
• Intermittent or no engagement of the compressor clutch (audible click absent when A/C is switched on)
• Fault code B064 displayed on the monitoring panel or retrieved via diagnostic scanner
• Battery drain issues in some cases if relay is stuck in closed position
• No other engine performance issues, as this is isolated to the HVAC electrical circuit

Potential Causes

The most common technical failures triggering B064 on used SK135SRLC-2 excavators include:

• Failed A/C compressor clutch relay (relay contacts welded, burnt, or corroded from age)
• Damaged wiring harness between the ECM and relay, particularly at flex points near the cab mounting where vibration causes insulation wear
• Corroded or loose connector pins at the relay socket or ECM connector (common in machines exposed to moisture or stored outdoors)
• Shorted compressor clutch coil drawing excessive current and triggering ECM protection
• ECM internal driver circuit failure (rare, but possible in high-hour used machines)
• Blown fuse in the A/C circuit power supply

How to Troubleshoot and Fix Code B064

Step 1: Visual Inspection and Connector Check Locate the A/C compressor relay (typically in the cab fuse/relay panel). Inspect the relay socket and all associated connectors for corrosion, bent pins, or moisture intrusion. On used excavators, check the wiring harness routing from the relay to the compressor clutch for abrasion, cuts, or exposed copper at movement points.

Step 2: Relay and Fuse Testing Remove the A/C relay and test with a multimeter set to continuity mode. Check for proper resistance across coil terminals (typically 70-90 ohms) and verify switch contacts close when 12V is applied. Replace if readings are out of specification. Verify the dedicated A/C fuse (usually 10-15A) has continuity and isn't blown.

Step 3: Circuit Voltage Testing Using Kobelco diagnostic software or a multimeter, measure voltage at the relay socket with ignition on and A/C requested. You should see battery voltage (12-14V) at the power supply terminal. Test the ECM control signal wire for proper switching voltage (typically 0V when off, 12V when commanded). If voltage is present but clutch doesn't engage, test compressor clutch coil resistance (typically 3-5 ohms).

Step 4: Harness Continuity Check For used machines with high vibration hours, perform a wiggle test while monitoring circuit continuity between the ECM connector and relay. Intermittent opens indicate harness internal breaks common in older SK135 models. Pay special attention to harnesses near the cab pivot points and engine firewall pass-throughs.

Disclaimer: This guide provides general troubleshooting procedures. Always consult the official Kobelco service manual for your specific machine serial number and electrical schematics. If unfamiliar with electrical diagnostics, consult a certified Kobelco technician to prevent ECM damage or safety hazards.