What is Kobelco SK135SR-2 Fault Code B114?

Fault Code B114 on the Kobelco SK135SR-2 excavator indicates a malfunction in the cab air conditioning system circuit, specifically relating to the A/C compressor clutch relay or its control circuit. This code is logged when the excavator's Electronic Control Module (ECM) detects an abnormal voltage reading or open/short circuit condition in the wiring between the control unit and the A/C compressor relay.

While not directly impacting hydraulic or engine performance, this fault affects operator comfort and can indicate broader electrical system issues in used machines. The Kobelco SK135SR-2's climate control system integrates with the main electrical harness, making proper diagnosis essential to prevent cascading electrical problems that could affect other cab functions or instrument panel operations.

Common Symptoms

• A/C system completely non-functional despite controls being activated; compressor clutch fails to engage
• Intermittent A/C operation where cooling works sporadically before stopping entirely
• Warning indicator illuminated on the instrument cluster (check engine light or dedicated climate control alert)
• No audible click from the compressor relay when A/C button is pressed
• Blower fan operates normally but air remains warm, indicating compressor-specific failure

Potential Causes

The most common causes for Code B114 in used SK135SR-2 excavators include:

• Failed A/C compressor clutch relay due to contact wear or coil burnout (common after 4,000+ operating hours)
• Corroded or damaged wiring harness connections at the relay socket or ECM connector—particularly vulnerable in machines exposed to wet or corrosive environments
• Worn harness routing where cab tilt mechanisms or engine vibration cause wire chafing near the relay mounting location
• Faulty ECM output circuit controlling the relay signal (less common but possible in high-hour machines)
• Low refrigerant pressure switch triggering protective circuit shutdown, indirectly causing control circuit faults
• Blown fuse in the A/C compressor circuit within the main fuse box

How to Troubleshoot and Fix Code B114

Step 1: Visual Inspection Begin by locating the A/C compressor relay in the main fuse/relay box (typically under the operator seat or right-side panel). Inspect all connector pins for corrosion, bent terminals, or heat damage. On used excavators, pay special attention to harness routing where wires pass through the cab mounting points—these are known wear points on the SK135SR-2.

Step 2: Relay and Fuse Testing Remove the A/C compressor relay and test it using a multimeter. Check for continuity across coil terminals (typically 80-120 ohms resistance). Swap with an identical relay from another circuit temporarily to verify functionality. Inspect the dedicated A/C fuse (usually 10-15A rating) for blown elements.

Step 3: Wiring Harness Voltage Check Using Kobelco diagnostic software or a quality multimeter, backprobe the relay socket with ignition on and A/C activated. Verify 12V supply voltage at the power terminal and proper ground continuity (less than 0.5 ohms). Check the ECM control signal wire for switching voltage (should toggle between 0V and 12V when A/C is engaged).

Step 4: ECM and Pressure Switch Verification If relay and wiring test normal, verify refrigerant system pressure using A/C manifold gauges. Low refrigerant triggers the pressure switch, preventing compressor engagement. Finally, test ECM output at pin location specified in service manual—faulty output drivers require ECM repair or replacement.

For used excavators: Always clean and apply dielectric grease to all connectors during reassembly to prevent future corrosion issues.

---

Disclaimer: This guide provides general troubleshooting information. Always consult the official Kobelco service manual for your specific machine serial number and seek professional assistance for complex electrical diagnostics or refrigerant system work requiring EPA certification.