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Car with no air conditioning

Car Air Conditioning / November 10, 2019

AC gauge setThere is never a good time for your air conditioning in your car to stop working, but it typically seems to happen in the dead heat of summer. If your AC system has either quit working or has stopped working well, you're faced with driving your vehicle around with the windows down - which brings little relief when it is hot outside. Having some knowledge about how the air conditioning works in your vehicle can help you get the system functioning again.

Part 1 of 9: Understanding the AC system and components

Your car's air conditioning system works just like a refrigerator or your home air conditioning. The purpose of the system is to remove hot air from the inside of your vehicle. It consists of the following components:

Component 1: Compressor. The purpose of the compressor is to pressurize the air conditioning system and circulate the refrigerant. It's located at the front of the engine and is typically driven by the main drive belt.

Component 2: Condenser. The condenser is located in the front of the radiator and is used to remove heat from the refrigerant.

Component 3: Evaporator. The evaporator is located inside the dash of the vehicle and is used to absorb heat from the interior of the car.

Component 4: Metering device. This is known as a metering tube or an expansion valve and can be located either under the dash or under the hood near the fire wall. Its purpose is to change the pressure in the air conditioning system from high pressure to low pressure.

Component 5: Hoses or lines. These consist of metal and rubber lines to carry the refrigerant.

Component 6: Refrigerant. Typically, all systems today contain R-134A refrigerant. This can be purchased over the counter at most auto parts stores. Older vehicles were built with R-12, which is no longer used because it contained high amounts of ozone depleting compounds. If you have a license and certification you can still purchase this, though most people opt to retrofit this system to the newer R-134A refrigerant.

vehicle parked on a level surface with wheel chocks around the rear tireThough these are the primary components of the air conditioning system, your vehicle has a series of electrical circuits that allow it to function, as well as a dash system that contains numerous doors that move within the dash that can affect effectiveness. Below are the most common causes of poor air conditioning performance and what can be done to get you comfortably back on the road.

Part 2 of 9: Tools and safety

When performing any air conditioning system service you must have the proper tools - and exercise caution when when using them.

Reason 1: High pressure. The air conditioning system is filled with high pressure refrigerant, and can operate at over 200 psi, which can be very dangerous.

Reason 2: High temperature. Parts of the AC system can reach well over 150 degrees Fahrenheit so be very careful when coming in contact with parts of the system.

Reason 3: Moving parts. You must watch out for moving parts under the hood while the engine is running. Keep all articles of clothing tightly secured.

Materials Needed

  • Air conditioning manifold gauge set
  • Gloves
  • Refrigerant
  • Safety Glasses
  • Warning: Never add anything but the recommended refrigerant to the AC system.
  • AC quick connectionsWarning: Always wear safety glasses when servicing any pressurized system.
  • Warning: Never install the gauges with the system running.

Part 3 of 9: Performance check

Step 1: Park your vehicle on a level surface.

Step 2: Place the wheel chocks around the driver side rear tire.

Step 3: Open the hood.

Step 4: Locate the air conditioning compressor.

  • Tip: The compressor will be mounted towards the front of the engine and is driven by the engine drive belt. You may need a flashlight to be able to see it. It's one of the larger pulleys in the system and has a separate clutch located on the front of the compressor. It will also have two lines connected to it. If you have trouble locating it then start your engine and turn the air conditioning off. The compressor pulley will be spinning with the belt, but you should notice that the front of the compressor clutch is stationary.

Step 5: Turn on the AC. Turn the air conditioning on in the vehicle and see if that clutch that was previously stationary is now engaged.

Step 6: Turn the fan to Medium. If the compressor clutch engaged, return to the inside of your vehicle and turn the fan speed to Medium.

Step 7: Check the air temperature. See if the temperature of the air coming from the main dash vents is cold.

Read the parts below to understand the different conditions that you may see:

  • No air coming out of the vents
  • The compressor clutch not engaging
  • The clutch is engaging but the air not cold
  • The system is empty on refrigerant
  • The system is low on refrigerant

driver of a car working the control panelPart 4 of 9: No air comes out of the dash vents

When performing your initial check, if air does not come from the center dash vents or if the air is coming from the wrong vents (such as the floor or windshield vents) then you have a problem with the interior climate control system.

  • Airflow problems can be caused by anything from a blower motor problem to an electrical issue or a module failure. This would need to be diagnosed separately.

Part 5 of 9: The compressor clutch does not engage

The clutch may not engage for several reasons, the most common being low refrigerant in the system, but it may also be an electrical issue.

Reason 1: Voltage. Voltage is not sent to the clutch when the air conditioning is turned on due to an open circuit in the electrical circuit.

Reason 2: Pressure switch. An air conditioning system pressure switch can disrupt the circuit if certain pressures are not met or if the switch is failing.

Reason 3: Input issue. More up to date systems are computer controlled and use numerous other inputs including vehicle interior and exterior temperature to determine whether or not to turn the compressor on.

You need to determine if there is refrigerant in the system.

Step 1: Turn the engine off.

Step 2: Install the gauges. Install the gauge set by locating the high and low side quick connections.

  • Tip: The location of these vary on every car, but most of the time you will find the low side on the passenger side of the engine compartment and the high side towards the front. The size of the fittings are different so you will not be able to install the gauge set backwards.

Step 3: Observe the pressure readings on the gauges.

  • Warning: Do not check for pressure by pressing on the fitting to see if refrigerant comes out. This is dangerous and it is illegal to vent refrigerant into the atmosphere.
  • If the reading is zero you have a major leak.
  • If there is pressure but the reading is below 50 psi then the system is low and may just need to be recharged.
  • If the reading is above 50 psi and the compressor is not engaging then there is either a problem with the compressor or you have an electrical system failure that needs to be diagnosed.

Part 6 of 9: The clutch engages but the air is not cold

Step 1: Turn the engine off and install the gauge set.