Toyota 4Runner HVAC Mystery: Evaporator, Expansion Valve, and a Sleepless Night Diagnosis

The Puzzling AC Problem

• ❄️ A 2019 Toyota 4Runner with over 100,000 miles presented an AC issue that only occurred after 2-3 hours of continuous driving, making it difficult to diagnose at the shop.
• 💨 The symptom was a complete stop of airflow from the vents, despite the blower motor running, suggesting a freezing evaporator.
• 🛠️ Initial diagnostics showed perfect pressures and charge, with no apparent blockages, leading to a challenging and time-consuming investigation.

Dash Removal and Vehicle Simplicity

• 🚗 The video details the process of removing the dash on a 5th generation Toyota 4Runner, highlighting its surprisingly basic and simple design, which has remained largely unchanged since 2010.
• 🧩 The harness behind the dash is noted as being unusually small for a vehicle designed to be produced until 2024, indicating a less complex electrical system compared to modern cars.
• ⚠️ A safety concern was identified with an aftermarket charger being grounded to an airbag component, which was subsequently relocated.

Diagnosis and Expansion Valve Suspicions

• 🥶 The problem was eventually reproducible after about 30 minutes of driving from a cold start, leading to the evaporator freezing, particularly around the lines to the expansion valve.
• 📉 Gauges revealed the low side dropping into a vacuum, a classic sign of a blockage, often indicative of a faulty expansion valve.
• 💰 Despite the car not being particularly old (6 years), the expansion valve was suspected, and the customer, frustrated by two summers without AC, agreed to the repair despite the risk.

The Unexpected Twist: Compressor Clutch Issue

• 🤯 After replacing the evaporator and expansion valve, the AC still failed, causing sleepless nights and a personal challenge for the technician.
• ⚙️ The breakthrough came when the compressor was found to be engaging even with the AC turned off, and later, with all wires disconnected.
• 🧐 Investigation revealed that the compressor clutch, previously replaced by a dealership, was missing shims, causing an incorrect air gap that led to it locking up when hot.

Resolution and Lessons Learned

• ✅ Replacing the missing shims resolved the immediate compressor issue, but the newly installed expansion valve subsequently froze, indicating it was likely damaged by the compressor problem.
• 🔁 The entire job, including the evaporator and expansion valve replacement, had to be redone, but this time with a clear understanding of the root cause.
• 👍 The 4Runner's design is praised for its simplicity and reliability, making repairs, though sometimes complex, manageable for those familiar with the brand.