What is Kobelco SK135SR-2 Fault Code B163?

Fault Code B163 on the Kobelco SK135SR-2 excavator indicates an abnormal signal from the air conditioner pressure switch circuit. This diagnostic trouble code (DTC) is triggered when the machine's electronic control unit (ECU) detects voltage irregularities, open circuits, or short circuits in the air conditioning pressure switch wiring or the switch itself.

This code specifically monitors the refrigerant pressure sensor that protects the A/C compressor from operating under unsafe high or low-pressure conditions. While this fault doesn't directly affect hydraulic or engine performance, it disables climate control functionality and may indicate broader electrical issues in used machines. For operators working long shifts in extreme temperatures, addressing this code is essential for cab comfort and maintaining resale value on the secondary market.

Common Symptoms

• Air conditioning system completely inoperative – compressor clutch won't engage regardless of cab temperature settings
• Warning indicator illuminated on the instrument cluster (typically an A/C-related light or general malfunction lamp)
• Intermittent A/C function that cuts in and out, particularly during hot ambient conditions when refrigerant pressure fluctuates
• No abnormal engine performance issues – hydraulics, travel functions, and diesel engine operation remain normal
• Fault code stored in ECM memory even after A/C system appears to function temporarily

Potential Causes

The most common technical failures triggering B163 on used SK135SR-2 excavators include:

• Faulty A/C pressure switch – internal contacts corroded or mechanically failed (common after 5,000+ operating hours)
• Damaged wiring harness near the condenser or compressor mounting area where vibration and heat cause insulation breakdown
• Corroded electrical connectors at the pressure switch itself – moisture ingress is frequent in machines stored outdoors
• Low refrigerant charge causing pressure switch to remain open due to insufficient system pressure
• Shorted wiring where harness rubs against frame components near the engine bay or right-side service panel
• ECU software glitch (rare) or poor ground connection at the cab's main electrical junction

How to Troubleshoot and Fix Code B163

Step 1: Visual Inspection and Connector Check
Locate the A/C pressure switch mounted on the refrigerant line near the receiver-dryer (typically on the right side of the engine compartment). Inspect the two-wire connector for corrosion, bent pins, or moisture. Clean contacts with electrical contact cleaner and dielectric grease. Check the wiring harness routing for chafing points against sheet metal or hydraulic lines – this is a known wear point on SK135SR-2 models with 3,000+ hours.

Step 2: Electrical Testing with Multimeter
Disconnect the pressure switch connector. Using a digital multimeter, check continuity across the switch terminals with the A/C system pressurized (engine running, A/C engaged). The switch should show continuity (closed circuit) when system pressure is within normal range (typically 30-350 psi). If the switch remains open or shows infinite resistance, replace the pressure switch (Kobelco part number or quality aftermarket equivalent).

Step 3: Circuit Voltage and Ground Verification
With the switch disconnected, check for battery voltage (12-14V) on the supply wire from the ECU using your multimeter. Verify solid ground on the return wire. If voltage is absent, trace wiring back toward the cab main harness – look for broken wires inside protective loom near bulkhead pass-throughs. For used excavators, corrosion at ground points behind the operator's seat is a frequent culprit.

Step 4: Refrigerant System Pressure Check
Connect A/C manifold gauges to service ports. With engine at operating temperature and A/C on MAX, verify pressures: low side should read 25-45 psi, high side 175-250 psi (ambient dependent). Low readings indicate refrigerant leak; excessively high readings suggest condenser blockage or cooling fan failure. Address refrigerant issues before concluding switch is faulty.

Step 5: Clear Code and Functional Test
After repairs, use Kobelco diagnostic software (ITCS or compatible scan tool) to clear stored fault codes. Operate the machine through multiple on/off A/C cycles while monitoring live data. Code B163 should not return if repair was successful.

Disclaimer: This guide provides general diagnostic procedures for experienced technicians. Always consult the Kobelco SK135SR-2 service manual for model-specific specifications. Refrigerant handling requires EPA 609 certification. If unfamiliar with electrical diagnostics or A/C systems, consult a certified Kobelco technician to prevent equipment damage or personal injury.