Car care advice

What Is Wrong with My Air Conditioning?

CAUTION: Only qualified/licensed mechanics should work on A/C systems. Refrigerant gases are under high pressure and can cause injury if not handled properly!

The Air Conditioning system is comprised of two main systems:

  1. Control System—Control panel (control module), electrical wiring, sensors, and the temperature/airflow controls
  2. A/C Refrigerant System—A/C compressor, evaporator, condenser, refrigerant, and the A/C hoses

Air Conditioning Is Not Blowing Cold Air

As the temperature outside warms up, this is the most common complaint about air conditioning systems. There are many causes for the A/C to stop working and we are going to address some of the more common ones here. To have an understanding of how the A/C system operates.

Low Refrigerant
If the airflow from the vents is okay, but the air is not cold, you might have a leak in the refrigerant system. One way you can verify this is by listening to the A/C compressor. You should hear an audible click from the engine area when the A/C is turned on—this is the A/C compressor clutch engaging, which allows the compressor to operate. When a system is low on refrigerant, the compressor will cycle on and off frequently. If the system is very low, the compressor will not turn on at all. The system must be checked for leaks—any leak found should be repaired and the system recharged.

How to find a leak:

  • Listen for a hissing sound from the A/C system
  • Look for oil residue from or around A/C hoses and pipe fittings
  • Inspect the condenser for road damage (in front of the radiator)
  • Use a special tool that can detect A/C refrigerant gas
  • Use an infrared light to detect ultraviolet dye in the refrigerant (if previously added)

These methods can all be used but the size and location of the leak will likely determine which will be most effective.

Compressor Off, Refrigerant Level Okay
The A/C compressor must turn on for the A/C system to work. The A/C compressor belt and the electrical circuit to the compressor must be in good condition. If the belt is okay, the mechanic will check for proper power supply to the compressor. If that checks out, then the compressor has likely failed and may need replacement.

If the power supply is not present, the problem might be:

  • Defective wiring or fuse
  • Bad pressure switch
  • Bad control module
  • A/C operation criteria has not been met:
    1. Low refrigerant pressure (low refrigerant or low pressure switch)
    2. Outside temperature too low (ambient temperature sensor)
    3. High refrigerant pressure (engine temperature too high/blockage in refrigerant system)
    4. Engine at full throttle (throttle position sensor)

Something Is Wrong with the Airflow from the Vents

Air flow is directed through passageways in the dashboard by using flaps and doors. These flaps and doors are controlled using a few methods:

Cable Operation
These control systems are quite simple. You have a lever or knob, a cable, and a cable controlled door/flap. When you move the lever or knob, the cable opens and closes the door, changing the direction of the airflow. The problem is usually broken cables, but the controls can break as well.

Vacuum Operation
These systems use vacuum to operate a vacuum motor (or diaphragm), which in turn operates a door or flap. The controls can be mechanical or electronic, but the system will use vacuum hoses to transmit vacuum to the vacuum diaphragms. Most of the time, the problem is a vacuum leak. Typically, when these systems lose vacuum, the airflow is automatically directed to the windshield—this may be constant or it can occur when you are driving only.

Electrically Operated
Most newer vehicles have an electrically controlled system, which uses electric motors to change the door position. A control module will send a voltage signal to the appropriate electric motor, which opens and closes the door accordingly. Some vehicles can have problems with the motors, while others have control module issues. Whatever the cause, these systems take electrical diagnostic skills to be able to diagnose and repair.

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