Nowadays, almost all machines come equipped with air-conditioning systems, except for open-cabin naturally ventilated models. When I first started in on-site CAT technical service more than twenty years ago, this was almost unimaginable. Back then, only CAT machines offered air-conditioning as standard, aiming to improve work efficiency, not simply for operator comfort. I once remarked: when operators no longer run machines bare-chested, that would signal our country had become wealthy. At that time, most brands offered air-conditioning as an optional feature costing 20,000–30,000 RMB, and the same applied to trucks on the highway.

Today, air-conditioning is standard on machines (excluding small knock-off brands—don’t even try to fool me!). Without AC, it’s difficult to hire operators; they would walk away at the mere mention of no air-conditioning.

For this discussion, we focus primarily on cooling. Only in northern regions is winter heating considered important. For example, operating a 40-ton excavator with a purely air-cooled engine in extreme cold was extremely challenging. Operators had to open windows, wear thick coats, boots, and fingerless gloves, and frequently get out to exercise for warmth.

Now, air-conditioning comes standard, and almost all operating components will eventually develop issues. I won’t cover full AC system repair here but will explain maintenance tasks that operators can perform to prolong system life.

General Principles

• Factory-installed air-conditioning is engine-driven, using the engine to drive the compressor. This follows basic energy conversion laws: energy flows from high to low, much like an apple falling due to gravity.

• Proper maintenance is essential—neglect leads to reduced cooling, overheating, or premature component failure.

Recommended Maintenance Practices

1. Check compressor belts regularly:

   • Adjust tension or replace as needed.

   • If squealing persists after adjusting, rule out tensioner bearing issues. Belts are wear items—don’t try to save money here.

2. Monitor the dryer sight glass during cooling:

   • Small intermittent bubbles are normal. Continuous bubbling or no flow may indicate system performance issues.

3. Maintain the air intake filter carefully:

   • A dirty filter can block the evaporator, causing poor cooling or frequent compressor clutch disengagement.

   • A clogged evaporator is hard to clean, and most AC faults originate here. Do not skimp on filter maintenance.

4. Check condenser and cooling performance:

   • Blocked condensers can overheat the system and trigger compressor cut-offs or fault codes.

   • You can check temperature differences across the condenser or blow compressed air through it. Do not disconnect high- or low-pressure lines. Avoid high-pressure water, which can bend fins.

5. Cooling efficiency:

   • Poor cooling does not always mean low refrigerant. At 1500 RPM, typical system pressures are ~0.15 MPa (low) and 1.5 MPa (high). Deviations can reduce cooling efficiency.

6. Winter operation:

   • Even when not using cooling, run the AC system weekly for a few minutes.

   • This circulates the compressor oil with the refrigerant, lubricating seals and preserving sealing performance. Lack of this practice is the main reason refrigerant loss occurs after winter. The principle is the same as in home AC units.

7. Professional repair:

   • Have trained personnel perform repairs to avoid further damage. No matter how skilled, repairs rarely restore the system to original factory condition.

Summary:

Following these maintenance tips—clean filters, check belts, monitor refrigerant and pressures, occasionally run the system—will significantly prolong the service life of your AC system, reduce repair costs, and maintain comfort. Neglecting these simple measures leads to early failures, which are costly and preventable.