Why Does Your Truck’s AC Struggle in Summer? Common Causes and Fixes

You’re out on I-78 in the middle of July. Windows up, engine roaring, but your truck’s AC is blowing air barely cooler than the pavement outside. Sound familiar?

At George’s Truck Trailer and Tire Repair in Newark, NJ, we hear it all summer long—“Why isn’t my AC keeping up?” The truth is, summer doesn’t just stress out drivers. It puts HVAC systems to the test, and even small faults get exposed when temperatures spike. Here are the most common reasons your truck’s AC struggles during the heat, plus simple fixes to keep your cab cool when it matters most.

Low Refrigerant and System Leaks

Refrigerant is the lifeblood of your AC system. Without enough of it, you’ll lose cooling power fast, especially during peak summer loads. A vacuum test and proper recharge ensure you’re cooling at full capacity, even in 95°F Newark heat.

• Low refrigerant charge: Leads to weak cooling output and higher compressor stress.
• Leaky fittings or O-rings: Small refrigerant leaks often go undetected without a pressure test.
• Damaged condenser or evaporator coils: Reduce system efficiency and can trigger a complete system shutdown.
• Worn Schrader valves: Often overlooked, but can slowly bleed refrigerant out of the system.
• Old receiver-driers: When saturated, they allow moisture to enter and damage internal components.

Electrical and Sensor Malfunctions

Even if refrigerant levels are fine, electrical issues can limit your HVAC system’s performance. These components control how and when your AC operates, and failure can cause intermittent or complete loss of cooling.

• Blown HVAC fuses: Instantly disable the fan or compressor without warning.
• Faulty pressure switches: Prevent the compressor from engaging when readings are incorrect.
• Malfunctioning temperature sensors: Feed false data to the ECM, resulting in wrong blend door commands.
• Compressor clutch failure: Prevents refrigerant circulation entirely, even if the system is otherwise charged.
• Wiring corrosion: Common in coastal climates like New Jersey, disrupting signal flow to and from the HVAC control module.

These issues can usually be found quickly using an HVAC scan tool or multimeter—don’t guess when you can test.

Clogged Cabin Filters and Dirty Evaporators

If air is blowing weakly or smells off, the issue may be closer than you think. A clogged cabin air filter chokes off airflow and makes your AC feel underpowered, even when the system is otherwise healthy. And a dirty evaporator core can become a breeding ground for mold, reducing system efficiency and air quality. Replacing filters regularly and having your HVAC system cleaned seasonally ensures peak air output and protects your respiratory health during long hauls.

Overworked Systems in Idle-Heavy Conditions

In cities like Newark, stop-and-go traffic and long idle periods are brutal on AC systems. When the truck isn’t moving, the condenser fan does all the heavy lifting—and if it’s not working at 100%, system pressure skyrockets. Over time, this overworks the compressor and weakens airflow across the evaporator. If your AC starts strong but fades during idle, this is likely your issue.

Signs Your AC Needs Immediate Service

The earlier you catch these issues, the cheaper and faster the fix.

• The AC blows warm air even when fully engaged
• Cooling drops off after idling at lights or in traffic
• The compressor clutch doesn’t engage or cycle rapidly
• Strange odors are coming from vents
• Loud clicking, squealing, or buzzing when the AC is turned on
• Airflow feels weak or uneven between vents
• Defrost takes too long to clear the windshield

Why HVAC Preventive Maintenance Matters

Preventive maintenance for HVAC systems in heavy-duty trucks is essential for ensuring driver comfort, safety, and efficiency year-round. Regular inspections and cleaning of filters, evaporator coils, condenser fins, and blower motors prevent dirt buildup and airflow restrictions, improving cooling and heating efficiency inside the cab. Checking refrigerant levels, inspecting hoses for leaks, and verifying compressor operation help maintain optimal system performance, preventing costly repairs or downtime. Proactively servicing truck HVAC units not only extends their operational lifespan but also ensures a comfortable cab environment, reducing driver fatigue and improving overall productivity on long hauls.

Beat the Heat With Expert AC Repairs

When your truck’s AC struggles in the summer, it’s rarely random. It’s often tied to low refrigerant, electrical failures, or clogged airflow paths—all of which can be diagnosed and corrected with seasonal HVAC service.

At George's Truck Trailer and Tire Repair, we specialize in keeping commercial trucks cool through the worst of summer. From AC recharges to compressor diagnostics, we’ll make sure your HVAC system performs like it should, so you can focus on the miles ahead, not the temperature inside your cab. For more information, read our article on what roadside assistance shops should offer to their partners.