3 Car Refrigeration Testing Techniques You Need to Know

3 Car Refrigeration Testing Techniques You Need to Know Reputable Garage Thanh Phong Auto Hcm 2024
Latest update date: February 19, 09

What causes the car's air conditioning system to blow out hot air? Some possible causes include: Lack of air conditioning gas, problem with the compressor's magnetic clutch, stuck compressor, problems with the HVAC control box, sensors, actuators, etc.

It is impossible to list all the causes. I will point out some main causes and guide you so you can check at home before taking your car to a garage or dealer for repair.

Check the air conditioner circuit

When the magnetic clutch of the compressor does not work, we will check the fuse, the first air conditioner relay. To do this, we will find the relay box, the fuse inside the engine compartment of the car. The compressor relay is usually named A/C CLUTCH RELAY, the fuse will be written as A/C CLUTCH. Or if the manufacturer does not sign the name, we can find the snowflake icon to locate the fuse, the relay of the air conditioning system.

Figure 1. Below the Fuse Box Cover will show the location of the Air Conditioning System Fuse and Relay
Figure 1. Below the Fuse Box Cover will show the location of the Air Conditioning System Fuse and Relay

Once located, check to see if the fuse is blown. If the air conditioner fuse is broken, we replace it and continue to check. Once we have determined that the fuse is not faulty, we move on to testing the relay. 

To check whether the relay is still working or not, we will supply power to two small pins. If the relay makes a "tack, click" sound, the relay is likely still in use. To check more definitely, we use the VOM meter, check the continuity of two large pins, if the circuit is open, the relay is still good. The reason we do so is because the relay is used for a long time, the contacts inside it will burn or rust, making them not in good contact anymore.

Figure 2. Relay External and Internal Structure
Figure 2. Relay External and Internal Structure
Figure 3. Relay Pin Structure
Figure 3. Relay Pin Structure

If the relay is still good, then we move on to check the wiring. When we unplug the relay, now on the relay box there will also be two small pins and two large pins. We use an electric tester to check whether these two pins are always positive or not, specifically:

One of the two control pins will have a 12V pin, the other pin will be supplied to ground by the HVAC box or supplied to ground directly through the AC switch. One of the two contact pins will have 12V, the other pin will be connected to the magnetic clutch.

Figure 4. Using an Electrical Tester to Find 12V Pins
Figure 4. Using an Electrical Tester to Find 12V Pins

If all tests go well, we continue to check the power supply circuit to the magnetic clutch. Using a wire with a fuse, we jump the two contact pins again, if we hear the magnetic clutch close, the power supply circuit for the magnetic clutch has no problem.

If there is no problem with the power supply circuit for the magnetic clutch, check the control circuit for the compressor relay. We start the engine, turn on the AC switch, measure and check the remaining control pins, whether there is mass output or not. If yes, it means that the control circuit is no problem.

If that control pin is not supplied with mass, it means that the control circuit has a problem. The part of checking the air conditioner control circuit we will learn in the following section.

If, after performing all of the above checks, the air conditioning system still does not work, then we can conclude that there is no problem with the wiring, ground, 12V power or magnetic clutch. 

Check air conditioner gas

If your home does a home test without a gas meter, you can do a quick test by taking a small object, poking it into the gas charging port, if there is no gas leaking out, it means our car has been damaged. running out of air conditioning gas. 

Figure 5. Air Conditioner Gas Charging Port
Figure 5. Air Conditioner Gas Charging Port

To control the gas pressure of the air conditioning system, the manufacturer will arrange an additional pressure switch to measure the pressure in the system. Only when the system pressure is sufficient will the system be allowed to operate.

Figure 6. Pressure Switch Location
Figure 6. Pressure Switch Location

Check the compressor

Conventional compressors will have damage such as: Stuck, broken magnetic clutch, weak compressor.

In case the compressor is stuck, we need to replace the compressor, the outdoor unit, the dehumidifier and clean the inside of the entire system. If you do not replace all of the above parts, the repair garage will not cover your warranty. 

So why do we only have to replace the compressor when we have to replace so many parts?

Because when the compressor is stuck, it is possible to create metal debris, which circulates inside the system. If unfortunately it gets stuck in the outdoor unit, it may circulate in the system, destroying all the components. 

At this point, you will ask the question "Why not rinse the hot rig?"

Because the structure of the outdoor unit is aluminum tubes of very small size, rinsing is difficult to push away metal debris. It also takes a lot of time and effort.

Figure 7. The size of the cold gas pipes in the condenser is very small
Figure 7. The size of the cold gas pipes in the condenser is very small

As for the case of the magnetic clutch not closing, the cause may be due to the magnetic clutch itself being damaged or the electrical circuit having a problem.

Figure 8. Basic Circuit Diagram of Magnetic Clutch Control
Figure 8. Basic Circuit Diagram of Magnetic Clutch Control

 

Depending on the car model you are using, the circuit diagram may be slightly different. But the basic principle will be the same for all car models. If you are passionate about technology, want to check your car yourself but don't know where to start, you can sign up for a refrigeration course at the Automotive Technical Practical Training Center - Thanh Phong Auto.

Car refrigeration testing course will provide knowledge about refrigeration principles, control principles, modern air conditioning systems...

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