Air Conditioner Troubleshooting Guide & Diagnosis – MB Medic (2024)

Is your air conditioner A/C not working or blowing hot air? The Air Conditioner system can get very complicated in cars, but that doesn’t mean that you can’t perform some troubleshooting yourself. Maybe even charge the A/C system if needed. This article will overview the A/C system, common problems, and repairs you can perform independently. While the pictures in this article are of Mercedes Benz cars, this guide is written to apply to all makes and models.

Common A/C Problems
How the A/C System Works.
Troubleshooting the A/C
Common Air Conditioner Problems and Solutions
Technical Specs

• A/C Blowing Warm Air
• No pressure or low refrigerant levels in the A/C System
• Compressor Clutch
• FreonR134a leaks
• The A/C compressor is not engaging.
• Liquid lock of the compressor
• A/C blowing hot air
• Compressors switch on and then off very quickly.

One of the key components of the A/C system is the compressor. The compressor’s purpose is to add pressure to the system by compressing the refrigerant. The operation of the A/C in your car is based on the First Law of Thermodynamics if you want to learn the physics behind it. From the compressor, the fluid goes to the condenser. By flowing through the condenser, the refrigerant loses heat, which converts into a warm liquid from hot gas.

Next in the system is the receiver-drier, whose primary purpose is to remove moisture from the A/C refrigerant. After that, the refrigerant goes through the expansion valve. The pressure drops in the expansion valve, allowing the refrigerant to expand. The expansion of the refrigerant causes the temperature of the refrigerant to drop. This is the opposite process that the compressor performs. Put pressure into a fluid you will increase its temperature. Removing pressure from fluid causes it to lose temperature. So in the expansion unit, the refrigerant temperatures drop below the outside temperature. From here, the refrigerant goes to the evaporator.

The evaporator works similarly to the radiator, except in this case, instead of hot coolant, there is cold refrigerant flowing through the evaporator. The low-temperature refrigerant passes through the evaporator, which causes the evaporator to get cold. The air then blows through the evaporator, which makes it get cold.
This is the essential operation of the A/C system, so let’s move on to some troubleshooting tips.

Step by Step

1. Gather the right tools. You will need a Recharge Kit to purchase at the local auto parts store or online at Amazon. It has a gauge you will first use to test your A/C system. We recommend the Arctic Freeze Recharge kit because it contains two large R134a refrigerant bottles. One contains UV dye which you may need if you have a leak and are trying to find it.
2. Turn the A/C ON. If you have an Economy button, make sure that it is off. Ensure the fan is high, the temperature selector is turned to COLD, and the A/C and recirculate light indicators are on.
   • Set the temperature to cold, the lowest setting.
   • Set the cooling fans on high climate control.
3. Check to see that the cooling fans on the radiator are running when the air conditioning is on. Most cars are designed to have the radiator cooling fan kick in when the A/C is on.
4. Check the compressor has engaged. Identify the location of your compressor. Look at the puller, and you should be able to see if it is spinning or not. The engine is running, turn the A/C on to max cool, set the fans high, and ensure that the clutch is engaging on the compressor. The pulley spins any time the engine is running. The center part of the A/C pulley only engages when the A/C is on. If the clutch engages and disengages rapidly, the refrigerant may be low.
5. Locate the Low-Pressure A/C recharge port. Attach the hose from the A/C Recharge Kit and check the pressure. Ensure the car is running and the A/C is on while you get a reading.
6. If the system is low, then start recharging the system using the instructions that came with your recharge kit. Pay attention to the direction that you need to hold the can. Some kits ask that you keep the can upright, while others ask to keep it upside down. Follow the A/C recharge kit recommendation to avoid putting air into the system.
7. If the reading moves toward the normal range, continue until the system is charged.
   • If you are charging the system, but the gauge is not moving, you may have a large leak. You will need to use charge the system with some dye to find where the leak is.
   • If the system works but only for a short time, again, you have a leak that you need to locate and repair.
   • You have a minor leak if the system works for a few months. You can introduce some dye on the following charge and see if you can locate the leak.We recommend the Arctic Freeze Recharge kit because it contains two large R134a refrigerant bottles. One contains UV dye which you may need if you have a leak and are trying to find it.
   • As you charge the system, you may notice the A/C starts to work. The A/C system is designed to disengage the A/C if the pressure in the lines is too low. This happens to protect the system. The compressor could be disengaged because the system does not have enough refrigerant pressure to trip the low-pressure cutoff switch that cycles the compressor.
   • Be careful not to overcharge the system, either. This could be dangerous and cause problems to your A/C system. You should be charging the system while you have the car running.
   • If you have low pressure, then check for leaks. Leaks are the most common problem associated with the air conditioning system. Charge the system via the low-pressure port with a Leak Detection Kit like this so you can find the leak.
     • Hopefully, your system was low, and it is working again. If not, continue with these troubleshooting steps.
8. Check the fuses. Look under the hood or under the dash to find the fuses. Find the A/C fuse and make sure that it is not blown.
   
9. Next, check the clutch itself. The clutch may be bad. If Is there voltage going to the clutch? A cycling switch may be bad, a fuse may be blown, and the system may not have enough refrigerant pressure to trip the low-pressure cutoff switch that cycles the compressor.
10. Check the relays.
    
11. Check the operation of the climate control and the A/C button.
12. Check the cabin air filter to ensure that it is not clogged.
13. Check the blower fan. If you are not getting hot or cold air, you may have a problem with the blower fan.

NOTE:-

• The dye check will not work if the system is too low and the compressor is not cycling.
• There is also a high-pressure service port. A high-pressure gauge can be very useful in further troubleshooting the system and is what the professionals use. Your AC recharge kit will not work; it doesn’t fit on the high-pressure port.
• Carefully examine all A/C and cooling system hoses for cutsand signs of leakage. Leakage from A/C system hoses is often indicated by an accumulation of dirt and oil, particularly at connections and fittings.
• Ensure the condenser (in front of the radiator) is free of obstructions, such as leaves or insects. This could reduce airflow, resulting in reduced A/C performance. You can rinse the condenser clean with a garden hose.

Diagnosing problems with an air conditioning system can be very complicated. This section will cover some common problems associated with the A/C system. Always wear safety glasses and gloves. Keep all loose-fitting clothing and body parts away from moving parts. A professional mechanic or technician should be consulted for any problems not covered below.

The following is a general A/C system troubleshooting guide. Realize that it is generic, and many things listed here may not apply to the 944.

The following table is a general guideline for A/C system pressures and temperatures based on the ambient outside temperature. Remember that these are a guideline, and your actual temperatures and pressures will vary depending on the humidity in the air and the condition of your system.

References:

1. www.clarks-garage.com/shop-manual/hvac-02.htm
2. aircondition.com/tech/questions/82/Troubleshooting-with-Gauges-FAQ
3. www.aa1car.com/library/ac98.htm
4. www.aa1car.com/library/automatic_climate_control.htm
5. www.movacs.com/How%20it%20works/index.html