Rick's Free Auto Repair Advice

Fix the AC in your car: Troubleshooting Tips

How to fix the AC in your car yourself and save a bundle

Is your car’s air conditioning system not cooling like it used to? An AC diagnostic at a shop can cost as much as $400. However, with the right tools and tips, you can diagnose and fix your car’s AC yourself, saving a considerable amount of money. This guide will walk you through the essential steps to troubleshoot and repair your car’s AC problem on your own.

Refrigerant Leaks: The Root of Most Car AC Problems

It’s crucial to understand that when refrigerant leaks out of the system, some refrigerant oil also escapes. Depending on the type of leak and the ambient temperature when it occurred, your car’s AC system can also take in air.

The loss of refrigerant and oil, and the introduction of air, not only reduces cooling but can also damage other system components. For example, running your car’s AC when it’s low on oil causes accelerated compressor wear, resulting in the spread of metallic wear particles throughout the system. These particles clog the expansion devices, causing a further drop in cooling efficiency.

Air in an AC system always reduces cooling. Worse than the loss of cooling is the fact that air also brings moisture into the system. Moisture interacts with the oil and refrigerant to cause acids and sludge, causing further damage to the system.

When faced with a loss of cooling, many DIYers simply add more refrigerant to the system. While this provides a temporary increase in cooling, it doesn’t address the leak or the damage that’s already occurred, so the damage continues to worsen.

This article is designed to help you pinpoint the problem in your car’s AC system using professional methods, rather than a parts cannon approach.

Essential Tools for DIY Car AC Repair

To diagnose and fix car AC problems yourself, you’ll need the following tools:

1) Manifold Gauge Set: You can’t accurately diagnose an AC system using low-side pressure readings. Manifold gauges are inexpensive to purchase or rent. Find a reasonably priced manifold gauge set on Amazon.com. This kit comes with the gauge, hoses, and can tappers to recharge the system.

2) Temperature Probes: These are crucial if you get some cooling but not cold air. To diagnose this issue, you must test the temperatures around the AC system at various locations. Non-contact infrared thermometers won’t work well for these tests. This inexpensive multimeter with temperature probes will get you all the information you need to properly diagnose your car’s AC problem.

3) Analog Dial or Digital Thermometer: This tool measures the temperature of the air coming out of the center vent, giving you an accurate reading of how well the system is performing. You don’t have to spend a lot on a dial probe thermometer. This one on Amazon only costs $6.

Note: Ricksfreeautorepairadvice.com receives a commission on products purchased through the above links.

This image shows the tools needed to diagnose and fix a car's AC system

Getting Started: Diagnosing Your Car’s AC

Step 1: Identify the Refrigerant and Oil Type

• Most cars and trucks from the 1990s until around 2017 used R-134a refrigerant, which is inexpensive and readily available at auto parts stores.

• However, newer vehicles often use the more environmentally friendly R-1234yf, which is more expensive. You’ll want to find and fix any leaks to save money.

• Many hybrid and electric vehicles use an electric AC compressor requiring special oil. Attempting to recharge these systems with a DIY kit containing conventional oil risks damaging the electric compressor and potential electrocution. If recharging your hybrid’s AC, you MUST purchase refrigerant without oil.

Why know the refrigerant and oil type?

Because once you find and fix the problem, you’ll have to refill the system with the correct refrigerant and oil. Find refrigerant capacities and oil type and capacities using this chart.

Step 2: Check for a Magnetic Compressor Clutch or a variable displacement compressor

• Older AC systems used a magnetic compressor clutch to disengage the compressor when the AC was off or cooling demands were low

• Many modern vehicles have a “clutchless” variable displacement compressor. The pulley and compressor shaft rotate continuously while the engine runs, even with the AC off. An internal valve only permits refrigerant flow when the system is engaged. For more information on clutchless compressors, see this article.

Why must you know whether you have a clutch or clutchless compressor?

If you have a clutch-style compressor that’s not operating properly, you can’t conduct any further testing. You have to diagnose it first. The diagnostic procedure is different for a clutchless-style compressor. So you must know which type you have before proceeding.

Step 3: Check High and Low Side Refrigerant Pressures Using the Manifold Gauge Set

Refer to the following links for normal and abnormal pressure readings, as well as possible causes of abnormal AC pressures:

• Normal car AC pressures

• Abnormal AC Pressure Readings and Possible Causes

Step 4: Check the Superheat Temperature

Abnormal pressure readings from Step 3 indicate an underlying issue with the system that needs to be diagnosed. The best way to pinpoint the exact cause of the problem is to conduct a superheat test. Although some DIYers and professionals overlook this step, conducting a superheat test is the industry standard for pinpointing the source of air conditioning problems. Superheat temperature readings offer deeper insights into the system’s operation compared to pressure gauges alone, similar to how blood test results provide a comprehensive picture of a patient’s health condition.

Click here to learn what superheat is and what it can tell you about your car’s AC problems.

By following these steps and using the proper tools, you can pinpoint the problem and fix the cause of your car’s AC blowing hot air. Then, use these articles to learn how to fix/replace the component and fix it permanently, saving you time and money.

Remember, acting quickly to address any refrigerant leaks is crucial to preventing further damage and ensuring a cool, comfortable ride all summer long.

©, 2020 Rick Muscoplat

Posted on by Rick Muscoplat

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