How to Troubleshoot A/C Problems in Freightliner Trucks

by Alibaster Smith

Freightliner AC systems are much larger than most vehicle systems, and they use a larger condenser and an air compressor to cool the air. An evaporator is used on freightliner trucks as a heat exchange medium to move the heat generated by the system away from the air conditioning unit. The most common problem with a freightliner AC system is a leaking compressor. A specially trained mechanic should fix any problems with the AC system, but you can troubleshoot to verify that there is a problem.

Step 1

Turn the engine on and allow the truck to warm up to its normal operating temperature. The water temperature gauge needle should sit in the center of the upper and lower marks on the gauge. Because most freighliners use the engine's pulley system to power the air conditioner, the truck must be at normal operating temperature before the AC will work at its best.

Step 2

Turn the fan speed on low and turn the AC to the coldest setting. Freightliners use a simple dial on the HVAC control unit to control the setting of the AC system. On a freightliner, the sound of the compressor starting is unmistakable. You should hear a low "hum" followed immediately by the cooling fan turning on. If you do not hear the compressor, it may have failed or is leaking. Either of these two scenarios will require that the compressor be replaced.

Turn the fan speed on the highest setting and set the AC to the coldest setting. If there is no cold air, the system needs to be recharged by a professional truck mechanic. The mechanic pumps refrigerant into the AC system so that the compressor has something to compress.


  • Freightliner trucks normally have a water temp gauge in the center of the dash-making it easy to know when your truck's engine is warm.
  • The reason for failure on freightliners is almost always a leak in the compressor due to a failure at the cooling line to air compressor seal. This, in turn, causes the compressor motor to continue running while coolant leaks out of the system. Because the compressor needs refrigerant to operate safely, the motor ends up burning out and failing at some point.


  • If you think the AC system on your freightliner truck needs to be recharged, don't'use the unit until you have the system recharged because it could cause a critical failure of the compressor.

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