By Michael DeMarinis | Training and Development Manager
How does your A/C system work?
Let’s start with the basics. Your vehicle’s air conditioning system works by cycling refrigerant through a closed system that transforms it between high-pressure gas and low-pressure liquid to cool the air inside your cab.
Here’s a simplified version of the process:
The A/C compressor pressurizes refrigerant gas—typically R-134a or R-1234yf—into a high-pressure vapor. That vapor flows to the condenser, which uses airflow from the condenser fan to cool the vapor and convert it into a liquid.
Next, the refrigerant passes through a filter-drier, which removes moisture and contaminants. From there, it flows through an expansion valve, which reduces the pressure and sends it to the evaporator. Inside the evaporator, the refrigerant returns to a vapor state, absorbing heat from the surrounding air. That now-cooled air is then pushed through the vents and into your cab. The refrigerant, meanwhile, cycles back to the compressor to repeat the process.
Mobile A/C System Dos and Don’ts
1. Don’t: Use a quick-charge refrigerant can.
These DIY cans often include a “stop leak” additive, which can clog your A/C system internally and damage components like the compressor, expansion valve, or evaporator. Plus, they don’t allow for accurate pressure readings. If your system needs refrigerant, it’s likely due to a leak—meaning it needs professional attention, not a temporary fix.
2. Don’t: Leave your A/C on when shutting down your vehicle.
Always turn off the A/C before switching off the engine. Leaving it on can cause the compressor to jolt mid-cycle when the vehicle restarts, which may lead to premature wear or failure over time.
3. Don’t: Ignore strange odors coming from your vents.
Unpleasant smells are usually not due to a broken A/C system, but rather a dirty cabin air filter or buildup on the evaporator coil. Replacing the filter and cleaning the evaporator can usually solve the issue.
4. Don’t: Expect freezing cold air in extreme heat.
Mobile A/C systems typically cool air 20–30 degrees below the outside temperature. So, if it’s 100°F outside, the coldest air you can expect from your vents is around 70–80°F.
5. Do: Run your A/C when needed—it won’t hurt your fuel economy.
Many drivers worry that using A/C reduces fuel efficiency, but today’s systems are designed to minimize impact. The compressor cycles on and off rather than running constantly, which keeps the load on your engine low and fuel usage largely unaffected.
Need a professional A/C system check?
Stop by any Boss Truck Shop location and have your air conditioning system inspected or serviced by trained technicians. We’ll help keep you cool—no myths, no shortcuts, just quality service.