Car A/C Stopped Working? Some Auto HVAC Troubleshooting Tips

Now that the weather is warming up, the last thing you want to deal with is your car A/C not working. Since there are so many complicated parts in an auto HVAC system, it can be challenging to pinpoint which component is causing the problem. This blog should help you determine if low coolant is why your car A/C blows warm air or if you should schedule an auto HVAC service with your trusted service technician.

What Is Your Car A/C Doing?

There are several reasons why your car A/C may stop working. Figuring out what it is doing can help you identify which components may be to blame.

Blows Warm Air

Double-check the temperature settings when the A/C blows warm air from the vents instead of cold air. If that does not resolve the issue, then a problem needs your attention. A handful of A/C components may cause warm air to exit the vents, even on the coldest setting. They include:

• • Bad Compressor
  • Clogged Expansion Valve
  • Dirty Condenser
  • Faulty Blower Motor
  • Insufficient Refrigerant Level
  • Low Coolant
  • Malfunctioning Thermostat

Low Airflow From Vents

Insufficient airflow in the cabin can result in poor cooling, especially on a very hot day. The low airflow cannot keep up with the heat generated by your vehicle’s engine or the sun’s rays. Check the following components when your vehicle’s A/C vents have low airflow, even if you set the fan speed to high:

• • Blend Doors & Actuator
  • Blower Motor
  • Cabin Air Filter
  • Cooling Fan Blades

Unusual Noises

Your car A/C system contains lots of complex moving parts. When the blower motor or compressor clutch starts to fail, you may hear unusual noises when the A/C runs. Common sounds of a malfunctioning car A/C system include:

• • Clicking
  • Clunking
  • Grinding
  • Rattling
  • Screeching
  • Whining
  • Whirring

Weird Smells

If you notice weird smells inside your car whenever you run the air conditioning, there may be several issues going on. Leaking fluids, dirty air filters, and accumulated debris may contribute to foul odors in your car. Try to identify the types of smells to know where to put your efforts.

• • Musty, moldy, or swampy smells point to a dirty air filter, evaporator coil, or vents.
  • Sticky-sweet smells indicate a coolant leak either inside the cabin or in the engine compartment.
  • Engine exhaust should never enter the inside of your car through the A/C vents. If you smell exhaust fumes, schedule a diagnostic service right away.
  • Rotten egg odors indicate a malfunctioning catalytic converter. This event requires an immediate service inspection.
  • Gasoline smells inside your car’s cabin means there is a fuel leak. Gas fumes can harm your health, so open your windows and get your vehicle in for service as soon as possible.
  • Charred or burning smells can come from overheating parts, faulty electrical components, or other malfunctions. If there is smoke as well as a burning smell, pull over, turn off your car, and ready your fire extinguisher in case of flames.

Auto HVAC Troubleshooting Tips

Now that you have identified what your car A/C is doing (or not doing) let’s look at some troubleshooting tips to resolve the issue.

Low Refrigerant Level

Your car A/C may need recharging if there is an inadequate refrigerant level due to a leak in the system. Refrigerant most often leaks from a faulty hose or seal. The auto HVAC system is sealed and only works when pressurized adequately. Your vehicle’s HVAC system requires an inspection and possible refrigerant recharge every 6-7 years by a qualified service technician. Common symptoms of a low refrigerant level include:

• • Car A/C blows warm air
  • Clicking sounds while the A/C runs

Low Coolant

Driving with low coolant may cause your vehicle’s engine to overheat. Low coolant levels often include dashboard warning lights, a high-temperature gauge reading, and a malfunctioning auto HVAC system. Usually, leaking antifreeze produces a sweet-smelling odor and a brightly colored puddle (typically yellow-green, but it can be other colors depending on your vehicle type). If you suspect a leak, look for:

• • Leaking coolant inside the cabin (usually on the floorboards or mats near the condenser)
  • Leaking coolant under the vehicle

Dirty A/C Condenser or Radiator

If the A/C condenser’s external fins get dirty or clogged, the engine works harder due to reduced external airflow. Your vehicle’s engine may overheat, or the air conditioning system can malfunction. Common problems include:

• • Dirt, leaves, or other debris build up on the front grill or radiator
  • Dirt, pet hair, or other debris build up on the A/C condenser
  • Damaged or crushed cooling fins

Broken Car A/C Components

There are a lot of components in your auto HVAC system, and any of them can break and require repair or replacement. Let’s briefly review what each part does.

A/C Compressor

The A/C compressor rotates a main shaft on bearings that can fail and pressurizes the A/C system with seals that can go bad. If the compressor goes bad, it may not engage properly and can disperse metal shavings that can damage other A/C components. A damaged A/C compressor blows warm air out of the vents.

Compressor Clutch

The A/C compressor clutch uses a pulley to transmit power from the engine to the compressor on older model vehicles. It builds pressure inside your car’s A/C system, allowing the cooling process to proceed. A worn or broken compressor clutch or pulley will not run the air conditioning. NOTE: Newer model cars use a variable A/C compressor, which doesn’t have a replaceable clutch. The entire unit requires replacement when a variable A/C compressor gets worn or breaks.

Auto A/C Condenser

The A/C condenser transfers heat away from the auto HVAC system, so it usually sits in front of the radiator for maximum airflow. This exposed location means it can easily get clogged or damaged by road debris while driving. The condenser features cooling fins that can bend or break, reducing heat dissipation. A damaged A/C condenser may also leak refrigerant.

Control Unit

The A/C control unit sends the signals to the blend door actuator to change positions, to turn on the A/C compressor, and to the fans to cool the condenser.

If it goes bad, part of the functions may not work anymore, or the whole system may stop working.

Blend Doors & Actuator

The blend doors are flaps that direct hot or cold airflow into the cabin. They change direction depending on the air conditioning control setting in your dashboard. The actuator controlling the blend doors works by vacuum or electricity, which can vary depending on your vehicle type. A bad actuator will not respond to the A/C control setting to move the blend doors to change the air temperature.

Cooling Fans

Your car uses cooling fans (from the radiator or condenser) to cool down the A/C condenser. They get power from the fan motor and should rotate when you turn on the air conditioner. Broken and missing fan blades move less air and can reduce the efficiency of your car A/C.

Fan Motor or Blower Motor

A broken blower motor cannot move enough air volume to cool the cabin.

Pressure Switch

A bad pressure switch will prevent the auto HVAC system from cooling the air because it will not engage the compressor to pressurize the system.

Seals, Hoses, Belts

All the numerous components in your auto HVAC system connect with seals, gaskets, hoses, and belts. Most of them are made of rubber (or similar compounds) that wear out with age and heat exposure. When these parts fail, they require replacement – which may be difficult because they are hidden behind or within other components. 

Leaking Fluids

Your vehicle uses a lot of different fluids to operate safely and efficiently. Some auto HVAC systems can stop working when fluid levels become too low. Frequently checking fluid levels can help keep your car A/C working better all summer long. It’s common but not always normal to find the following fluids near or under your vehicle:

• • Coolant
  • Water Condensation
  • Engine Oil
  • Refrigerant (not usually seen as it turns to vapor)

Clogged Cabin Air Filter

Cabin air filters capture airborne debris (like pollen, smoke, ash, and fumes) before the air enters your car’s interior.  A clogged air filter can reduce your auto HVAC system’s efficiency and effectiveness. 

• • Interior smells stale or musty
  • Low airflow from vents
  • Air feels warmer than it should

Auto HVAC Repairs in San Diego, CA

Wentworth Automotive in San Diego, CA, specializes in auto HVAC repairs and services. We provide best-in-class customer service and are known for reliable and affordable auto care. Our technicians will gladly help diagnose any problem with your A/C system, such as low coolant, blows warm air, or smells weird.

Schedule A Car A/C Service

Did you know that postponing or ignoring your car A/C repair might damage other parts of your car? Delaying service can lead to expensive future repairs. Schedule your air conditioning service at the first signs of trouble to prevent additional wear and repairs.

Call our customer service reps at (858) 541-1044 or visit our website to schedule your auto HVAC service today!