Diagnosing and Repairing AC Issues in the John Deere 135C Excavator

[MikePhua]

The 135C and Deere’s Mid-Size Excavator Lineage
The John Deere 135C excavator was introduced in the early 2000s as part of Deere’s C-series lineup, designed to meet Tier II emissions standards while improving operator comfort and hydraulic precision. With an operating weight of approximately 30,000 lbs and a zero-tail-swing design, the 135C was built for urban excavation, utility trenching, and tight-access demolition. Its cab featured improved visibility, ergonomic controls, and a factory-installed HVAC system—making it one of the more operator-friendly machines in its class.
John Deere, founded in 1837, has sold millions of machines globally, and the 135C remains a popular choice in North America and Asia. The air conditioning system in this model is a sealed R134a refrigerant loop with an electric clutch compressor, expansion valve, evaporator core, and dual-speed blower fan. While generally reliable, the AC system can develop faults due to age, vibration, and environmental exposure.
Common Symptoms of AC Failure
Operators encountering AC issues in the 135C often report:

• Blower fan runs but no cold air
  
• Compressor clutch does not engage
  
• AC light on the control panel flickers or stays off
  
• Cabin temperature remains high despite system activation
  
• Refrigerant lines show uneven temperature distribution
  

Terminology clarification:

• Compressor clutch: An electromagnetic coupling that engages the compressor when the AC is turned on.
  
• Expansion valve: A metering device that regulates refrigerant flow into the evaporator.
  
• Evaporator core: A heat exchanger inside the cab that cools air as refrigerant evaporates.
  
• Low-pressure switch: A safety sensor that disables the compressor if refrigerant pressure drops too low.
  

In a 2021 excavation job in Arizona, a 135C’s AC failed during a heatwave. The compressor clutch was not engaging, and technicians found the low-pressure switch had tripped due to a slow refrigerant leak at the condenser fitting. After resealing and recharging, the system returned to full function.
Diagnostic Strategy and Component Testing
To isolate AC faults, technicians should follow a structured approach:

1. Check refrigerant pressure using a manifold gauge set. Low pressure indicates a leak or undercharge.
   
2. Inspect compressor clutch for voltage during AC activation. If no voltage is present, trace wiring back to the relay and switch.
   
3. Test blower fan speeds and verify airflow through the evaporator. Weak airflow may suggest a clogged cabin filter or failing motor.
   
4. Scan for fault codes if equipped with a diagnostic interface. Some Deere models store HVAC errors in the control module.
   
5. Inspect condenser and evaporator fins for debris or corrosion.
   
6. Check expansion valve operation by monitoring line temperatures. A failed valve may cause frost buildup or warm air output.
   

Recommended tools:

• R134a manifold gauge set
  
• Multimeter with continuity and voltage modes
  
• Infrared thermometer for line temperature tracking
  
• Leak detection dye and UV light
  
• Wiring diagram for HVAC circuit tracing
  

In a 2022 fleet inspection in Ontario, 15% of mid-size Deere excavators showed AC faults due to clutch relay failure. Replacing the relay and cleaning the connector restored compressor function.
Repair Options and Preventive Measures
Once the fault is identified, corrective actions include:
Electrical:

• Replace compressor clutch relay and test voltage
  
• Repair damaged wires and apply dielectric grease to connectors
  
• Replace cabin temperature sensor if readings are erratic
  
• Clean control panel contacts and inspect switch logic
  

Mechanical:

• Recharge system with R134a to factory spec (typically 2.2–2.5 lbs)
  
• Replace leaking O-rings and fittings
  
• Flush and replace expansion valve if metering is inconsistent
  
• Clean evaporator core and replace cabin air filter
  

Preventive tips:

• Inspect AC system quarterly, especially before summer
  
• Clean condenser fins with low-pressure air or water
  
• Use UV dye during recharge to monitor for future leaks
  
• Keep cab windows closed during operation to reduce thermal load
  
• Train operators to report weak cooling early
  

In a 2023 municipal fleet in Wisconsin, implementing an AC inspection checklist reduced HVAC complaints by 60%, especially during seasonal transitions when systems were reactivated after winter storage.
Conclusion
AC failure in the John Deere 135C is often a blend of electrical and refrigerant issues—hidden in a switch, sensor, or fitting. With structured diagnostics and attention to pressure, voltage, and airflow, technicians can restore cooling performance and operator comfort. In mid-size excavators, climate control is more than luxury—it’s a productivity tool. And for the 135C, keeping the cab cool means keeping the crew focused, safe, and efficient.