Why Is The A/C in My Car Not Working?

The most obvious indicator that your A/C isn't working properly is lukewarm air coming from the vents. The air conditioning is on, your temperature selector is set to cold, but the air blowing out is warm. Here are a few possibilities:

You’re Low On Refrigerant

This is the most common issue, and it means you have a leak. You have a few options to determine if this is the case. An A/C leak detector has the ability to detect escaping refrigerant vapors, and electronic refrigerant detectors, also called “sniffers,” are the most commonly-used A/C leak detection device. However, these tend to be very expensive and are mostly used by professional technicians. Refrigerant with UV dye is also available, which can be used with a specialized UV light to locate the leak. The UV light will cause the refrigerant dye to “glow” around the leaking fitting, hose, or other component. Finally, all A/C systems are designed to prevent the compressor from running if it is low on refrigerant, so you may need to recharge the system with refrigerant and run it for a few minutes to allow the UV dye to circulate throughout the system. If the A/C compressor fails to activate with an appropriate amount of refrigerant in the system, this may indicate a problem with the electrical system or A/C clutch, which we’ll detail further below.

You Have A Problem In The A/C Electrical Circuit

Most A/C systems today have a fairly complex electrical circuit. But ultimately, the system is designed to “cycle” the A/C compressor on and off based on the temperature desired by the driver and the temperature of the cabin or evaporator. You can usually hear the A/C compressor clutch engaging when you turn the A/C on. If you notice the clutch is not engaging at all, the most likely cause is the system is low on refrigerant, but if you have checked the refrigerant pressure and it is within specifications, then you may need to perform some electrical diagnostics using a voltmeter and/or test light.

You Have A Restriction Or Clog In The System

Many passages within your A/C system are very small, so small debris and particles can aggregate and form a restriction in the system. These may occur in the condenser, evaporator, expansion valve, or A/C hoses for a variety of reasons. The only way to locate the restriction is by using a set of A/C gauges to determine if the pressure on both the high and low sides of the A/C system is appropriate during operation.

A lack of airflow may not be as much of a problem with the air conditioning as it is with the climate control system in general. Low or no airflow through the vents of your vehicle likely indicates a problem with the blower motor system or the cabin air filter if your car has one.

Failing Blower Motor

A blower motor pushes the air through your car’s system. A failing motor may prevent any air from moving at all or may only works on the lowest setting.

• If no air is moving at all, check the fuse first


• If the fuse doesn’t need to be replaced, check the condition of the resistor. The resistor may be visibly burned or damaged due to the high heat of electrical resistance, causing the blower motor to only work on certain speeds


• If the resistor is in good condition, use a voltmeter to test the resistor switch or the blower motor

Cabin Air Filter

The cabin air filter is a maintenance item that should be serviced according to your owner’s manual, or as often as needed to keep the air you breathe inside your car free from most debris, pollen, and allergens. A clogged cabin air filter can limit airflow and not allow as much cold air to make it to the vents, making your A/C system work a lot harder to keep you cool.

If you’re experiencing any of these symptoms, or if you have more questions, feel free to stop by your local O’Reilly Auto Parts store.