JD 35D A/C Control Blinking Issue

[MikePhua]

The John Deere 35D excavator, a widely used model recognized for its compact power and versatility, sometimes encounters technical challenges with its air conditioning system. Among the reported issues is the air conditioning (A/C) control panel blinking when the A/C ON button is pressed, accompanied by a ticking sound from one of the relays located under the panel beneath the operator's seat.
Understanding the Problem
The blinking on the A/C control board combined with relay ticking often indicates an electrical or control system fault that prevents the A/C system from engaging properly. Relays serve as electrically operated switches controlling high-current circuits like the A/C compressor clutch. A ticking sound usually means the relay is repeatedly trying to engage and disengage but failing to maintain a steady connection.
Common Causes

• Faulty or weak relay: The relay responsible for switching power to the A/C compressor may be worn, causing it to chatter or click repeatedly.
  
• Inadequate voltage supply or electrical connection issues: Loose, corroded, or damaged wires can lead to intermittent relay activation.
  
• A/C compressor overload or mechanical failure: If the compressor clutch is seized or under excessive load, the relay may fuse in and out trying to power it.
  
• Control board malfunction: Problems in the electronic control unit (ECU) or circuit board behind the A/C panel can cause erratic signals.
  
• Low refrigerant pressure or sensor issues: Some models have pressure sensors that prevent compressor engagement under unsafe conditions.
  

Diagnostics and Troubleshooting Steps

1. Relay Identification and Testing
   Locate the relay panel beneath the seat and identify the relay linked to the A/C system. Relays can be tested by swapping with a similar known-good relay from another circuit in the machine or using a multimeter for continuity and coil resistance.
   
2. Voltage and Wiring Inspection
   Check for stable 12V supply to the relay coil and power input. Clean terminal connections and inspect all visible wiring for breaks or corrosion to ensure proper current flow.
   
3. Compressor Clutch Evaluation
   Engage the A/C while monitoring the compressor clutch engagement. If the clutch fails to engage or repeatedly cycles, manually test the clutch coil resistance and inspect for any mechanical binding.
   
4. Control Board Examination
   Inspect the A/C control board for signs of burn marks, cracked solder joints, or loose connectors. If possible, testing the control signals with diagnostic tools can isolate whether the problem lies with the board electronics.
   
5. Refrigerant and Pressure Sensors
   Low refrigerant levels or faulty pressure sensors can cause safety shutdowns of the compressor. Checking refrigerant charge and sensor readings is essential.
   

Technical Terms

• Relay: An electrically controlled switch that enables low current circuits to control higher current loads safely.
  
• Compressor clutch: A magnetic clutch that engages the compressor of the A/C system to pressurize refrigerant.
  
• Control board: The circuit board within the HVAC control panel managing input commands and electrical outputs.
  
• Refrigerant: The gas or liquid used in the A/C system to absorb and dissipate heat.
  
• Pressure sensor: A device measuring refrigerant pressure to ensure safe operation of the compressor.
  

Solutions and Maintenance Tips

• Replace any faulty relay with a high-quality equivalent or OEM part to ensure reliable switching.
  
• Repair or replace corroded or damaged wiring and connectors, using dielectric grease to reduce corrosion.
  
• Service the compressor clutch by cleaning contacts, checking coil resistance, and replacing worn components.
  
• Recharge the refrigerant to proper levels after vacuum and leak testing.
  
• Regularly clean the condenser and A/C filters to maintain efficient airflow and system performance.
  
• When suspecting control board failure, consult authorized service manuals or authorized John Deere dealers for board repair or replacement options.
  

A Related Story
An operator of a 2012 JD 35D reported the A/C system began blinking and making clicking noises when engaging the A/C. The culprit was traced to a relay cycling due to a slightly seized compressor clutch. Once the clutch was cleaned, and the relay replaced with a genuine OEM unit, normal operation resumed. This saved the operator from costly compressor replacement and prolonged the life of the HVAC system.
John Deere 35D Overview
Introduced in the early 2010s, the John Deere 35D compact excavator combines fuel efficiency, hydraulic power, and operator comfort. With approximately 35 horsepower and a rated operating weight near 8,000 lbs, it is suited for urban construction, landscaping, and utility work. Its HVAC system plays a critical role in operator comfort, especially in extreme weather conditions.
Summary Recommendations

• Start troubleshooting by diagnosing the relay and electrical circuitry related to the A/C control.
  
• Follow systematic checks of voltage, wiring integrity, and mechanical A/C components.
  
• Ensure refrigerant levels and sensors are within factory specifications.
  
• Periodic preventive maintenance helps avoid unexpected HVAC failures and maintains operator comfort.
  
• Maintain access to accurate John Deere service manuals and genuine parts to streamline repair and reduce downtime.
  

The blinking A/C control light and relay clicking in the John Deere 35D excavator highlight the importance of integrated electrical and mechanical diagnostics to restore reliable cooling performance efficiently and cost-effectively.