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9 Reasons Your Car AC Isn’t Blowing Cold Air

woman in hot car with broken air conditioning

Signs You May Need Your Car’s AC Repaired

Entering a hot car and sticking to the seats because the air conditioning isn’t working is something no motorist wants to experience on a scorching day. Sure, you could drive with the windows open and the fan blowing, just as drivers did back before automotive air conditioning became prevalent, but that’s not a comfortable solution, and it certainly won’t be popular with your passengers.

Air conditioning woes can range from major to minor. Here are the most common causes of broken car AC systems:

1. Low Refrigerant

This is the most likely issue when the air blows hot. Low refrigerant is typically caused by a leak; a worn hose or loose connection is often the culprit.

You can replenish the system using a recharge kit available at an auto parts store, but there are two downsides to that approach: One, there’s a risk of overcharging the system, which can adversely affect its performance. Two, you still won’t have found and fixed the leak that caused the problem in the first place.

car ac compressor
Car AC Compressor Credit: Getty / Aleksandr Kondratov

2. Faulty Compressor

If this key component fails, it brings the entire air conditioning system down. The compressor could have a bad clutch, which is a less-serious repair. In cars with a belt-driven AC unit, the clutch connects the compressor to the pulley that powers the system; it allows you to turn the compressor on and off. (If your AC unit is driven by an electric motor, as is the case in some hybrids and all EVs, it won’t have a clutch.) The problem could be as simple as a blown fuse.

3. Bad Pressure Switch

A pair of pressure switches monitor the refrigerant. If the pressure becomes too high or low, it will turn off the compressor for safety reasons, which will cause the system to stop working.

Car AC Condenser
Car AC Condenser / Credit: Getty / chiewr

4. Damaged Condenser

The component that cools the air conditioning refrigerant sits ahead of the radiator at the front of the vehicle and it can become clogged or suffer damage from debris striking it. Age and wear can also cause a condenser to fail. A car’s AC condenser will typically need to be replaced after 10 years or so under normal operation. 

5. Failed Condenser Fan

The condenser uses moving air to cool the system’s refrigerant. This pretty much takes care of itself when you drive the vehicle at higher speeds, but the condenser needs a fan to function at lower vehicle speeds.

If the fan stops working, you’ll notice a difference in how well the AC system cools the cabin while driving around town versus on the highway. You may also hear some banging or rattling, and you won’t hear the fan running after the car is parked.

6. Sensor Glitches

A vehicle’s climate control system relies on numerous sensors to deliver air at the proper temperature. Its performance will be compromised if one of these sensors fails.

Cabin Air Filter Clean and Dirty
Clean vs. Dirty Cabin Air Filter

7. Obstructed Cabin Air Filter

A car’s climate control system uses a filter to trap dust, pollen, and particles that might otherwise enter the cabin. If the cabin air filter is not changed on a regular basis, it can become clogged and will affect the system’s cooling abilities. 

8. Defective Blend Door Actuator

A vehicle’s air conditioning system uses a component called a blend door actuator that channels hot or cold air into the cabin. If you set the system for one and wind up getting the other, it could be because the actuator is malfunctioning.

9. Faulty Head Unit

If the rest of the system checks out, the main control unit (the part in the cabin with the temperature controls) may be at fault, perhaps sending the wrong signal. This could result from a problem with the wiring or, in the case of newer vehicles, the electronic signal that links the computerized temperature controls to the mechanical AC components under the hood.

car air conditioning and climate controls
Car AC Controls / Credit: Getty / ponsulak

How Much Does AC Repair Cost?

Some of the most serious problems can be costly to fix, but this can be money well spent when the temperatures are sizzling.

Here’s a look at some national average estimates to fix the most common air conditioning woes, courtesy of RepairPal.com. Prices will vary according to the cost of parts for your specific vehicle, local wage rates, and other factors. Estimates do not include taxes and related service requirements.

  • System Inspection: Up to $70 
  • Refrigerant Recharge: $120 to $155
  • Blend Door Actuator Replacement: $325 to $375
  • Cabin Air Filter Replacement: Up to $85
  • Compressor Replacement: $720 to $950
  • Compressor Clutch Replacement: $570 to $620
  • Condenser Replacement: $450 to $600
  • Condenser Fan Replacement: $385 to $475
  • Electronic Control Module Replacement: $380 to $400
  • Temperature Sensor Replacement: $320 to $400

DIY: Can You Fix Your Car’s AC Yourself?

Air conditioner repair is best left to the pros, but you can do some air conditioner maintenance at home. An air conditioning system will last longer if it’s properly maintained. 

Tips for Maintaining Your AC

  • Run the system for at least 10 minutes each week at its highest fan and lowest temperature setting, even in the coldest months of the year. This basic process helps lubricate the compressor and prevent leaks. While you’re at it, run the defroster for 5-10 minutes at a time to clear the system of any moisture or mildew.
  • Change the cabin air filter according to your vehicle’s maintenance schedule.
  • Have the refrigerant recharged every two years. This isn’t as easy as the first two steps, but there are kits available online with detailed instructions. 
  • Finally, don’t hesitate to take the car in for service if the climate control system isn’t working as expected.

How a Car’s A/C Works

Though AC systems have become more sophisticated over the years, with some offering up to four zones of individual temperature control, the basic technology of air conditioning remains more or less the same.

  • The system uses a compressor, which is driven by a pulley connected to the engine or, in electric cars, an electric motor attached directly to the compressor.
  • The compressor compresses low-pressure refrigerant gas to a high pressure.
  • The pressurized refrigerant gas flows into the condenser behind the car’s front grille, where a system of twisting tubes cools the refrigerant and turns it into a high-pressure liquid.
  • The high-pressure liquid refrigerant moves through an accumulator or receiver-dryer, which removes any water that might damage the system. 
  • The high-pressure fluid passes through an orifice tube or expansion valve. This allows the refrigerant to expand and cool so it can move to the evaporator core as a near-freezing low-pressure liquid. In the evaporator, the liquid converts back to a low-pressure gas.
  • A fan blows air over the evaporator and sends the cool air into the passenger compartment.
  • The low-pressure refrigerant gas flows back into the compressor where the process begins over again.

Next Steps

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