Is Your Vehicles A/C Not Working? Read This First!

This guide was written by a professional automotive mechanic with years of experience. It is intended to teach the reader how to diagnose and potentially fix their own vehicle's A/C system. Moreover, you will learn what to check before you take your vehicle into a repair shop for costly A/C repairs.

Why This Is Important?

Understanding how to check your own vehicle's A/C system can save you a large sum of money very easily. Professional A/C services can cost thousands of dollars due to complexity and specialty tools used by shops.

This article aims to show you what to check before handing your keys over to a shop. The aim is to help you decide whether you need to have it worked on at a shop, or not. You'll learn what to check, how to check it, and when to take it to a professional. You will also learn about the dangers of Freon.

A Little About Freon


While you can fix and/or diagnose your vehicle A/C yourself, there are times you need to leave it to the pros. Even if you intend on replacing the damaged part yourself, you will need a shop to discharge the A/C system. When working with your Air Conditioning system you are dealing with contents under low pressure, and contents under high pressure.

Refrigerant is a chemical known as Freon and is also found in your household air conditioners, and your refrigerator. There are different kinds of Freon as well, older cars typically use R-12.

However, unless your car is older than 1990 your car probably doesn't use R-12. Many modern cars use R-134A, and it has become the most common refrigerant. R-134A however is now being replaced more and more by R-134YF, this started 2013-2014.

Freon Safety Information

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Refrigerant Gas R22 Class 2.2 UN1018

Image Courtesy of GC Labels, Inc[/caption]Freon itself is no joke, it is a deadly gas that is tasteless and mostly odorless. When Freon is inhaled it can cut off vital oxygen to your lungs and your cells.

Limited exposure like a small spill on your skin or breathing near an open container is only mildly harmful. It is however recommended that you avoid coming into physical contact or breathe in any Freon. If you suspect your vehicle's A/C system is currently leaking Freon, you should seek the help of a qualified mechanic.

Freon is also harmful to the environment and considered one of the most significant environmental pollutants. If working with your vehicle's A/C system, it is advised to do the work in a well-ventilated area.

The writers at can not be held responsible for injuries or damage as a result of following this article. Always work within your own limits, and if you not comfortable doing the work, take it to a qualified professional.

How A Vehicles A/C Works

How A Vehicles A/C Works

While it is not necessary to understand how your A/C system works to follow this guide, if you would like to learn more about how your vehicle's A/C system works, you can read our article on the Complete Car Air Conditioning Guide [2021].You can also check out this video on Vehicles A/C systems, uploaded to YouTube by Garage Tech.

Stages of Diagnosing your Vehicles A/C System

Before we dive into diagnosing the system, we should set up some guideline information. First, it is highly recommended you read the above section "A Little About Freon" before attempting any A/C work. Second, your car's heater system, and A/C system are not the same, though they use the same vents.

Finally, water under your car when the A/C is running is normal, and should not be cause for concern. That water is your A/C condenser's condensation runoff and is completely normal.Here are some quick things we can do to attempt to correct your vehicles A/C system issues:

  • Check related fuses for the air conditioner system
  • Check to see if the compressor clutch is actually engaging
  • Verify the system pressure and recharge the system if needed

Checking Your Fuses

One of the simplest things you can do when something is not working is to check the related fuses. The fuses for your car, and where to find them, will be in your Owners Manual.

The website is also extremely helpful in locating and identifying what your fuses protect, and where they can be found. If you would like to read further on fuses, we go in-depth with them in our article "A Mechanic's Guide to How to Fix a Car Radio."

Make Sure The A/C Compressor Clutch Is Turning

Attached to the engine, and powered by the accessory drive belt (aka the Serpentine Belt, or Drive Belt) is the A/C Compressor. AC Compressor & A/C Clutch For Nissan Sentra 2013 2014 2015 2016 2017 and Nissan Rogue Sport 2017 - BuyAutoParts 60-03816NA New: Automotive

This is the typical design of an A/C Compressor, it runs off the drive belt via the pulley (shown in black). If you look at the image of the compressor above, you will notice the 3 silver blade-like objects on the end of the pulley. When the engine is running, the pulley will spin with the belt, but just because the pulley is spinning, does not mean the compressor is operating.

For the compressor to be operating, the compressor clutch has to engage. Speaking of the clutch, make sure to check out our blog post about everything you should know about the clutch pedal. How do you know if the compressor clutch is engaging? Well, just look at those blades, if those are spinning, your compressor clutch is engaged, and your compressor is operational.

This does not necessarily mean it is operating properly or creating compression, but at least we know that it is spinning. Note that your compressor clutch might not engage if your system is low on refrigerant. So, how do we make sure the clutch is spinning? It is simple, just follow the mini-guide below:

Quick Vehicle A/C Compressor Diagnosis

  1. Start the car
  2. Turn the fan to its highest setting
  3. Set the temperature to its lowest setting
  4. Turn on the a/C (And max A/C button if equipped)
  5. Examine the compressor, watch to see if the clutch engages and starts spinning

WARNING: The belt in your engine spins at high speeds, do not put your hands near the belt with the engine running, do not let your hair dangle in the engine bay, do not less loose jewelry dangle into the engine bay.

You may need to keep an eye on the compressor for a little bit of time, it might not engage immediately. You can also tell when it engages because your engine will start running a little differently as it takes the extra load by driving the A/C compressor.

Verify Vehicles A/C System Pressure/Recharge

If your fuses are in proper order, and your compressor is engaging the clutch, it might be time to recharge your A/C system. Note again that your compressor might not engage if the system is low on refrigerant, so before you send the car to a mechanic, consider checking the charge of the A/C system.

A Freon/Refrigerant recharge kit will run you $40-$60, well under a repair shop's cost, and can be used easily. First, you will need to acquire your recharge kit, I personally recommend InterDynamics A/C Pro. The A/C Pro version comes with a reusable dispenser, saving money if you need to recharge again later.

There is plenty of other options out there, but for my customer's cars, I only trust A/C Pro to get the job done right. Let's get right into how to check and charge (if needed) your vehicle A/C system.

Awareness of Changing Refrigerant Types

Before we go buying a recharge kit, we first need to determine what refrigerant your vehicle takes. If you look in your manual it should tell you, looking it up online is also a great resource. The easiest place I find to look is under the hood.

You would find a label that looks something like the image above. Note that it shows the Refrigerant type next to the snowflake. Unless your car was manufactured before 1990, you most likely are using R-134A or R-134YF.You also might want to pick up an A/C Thermometer, it is not required, but it will certainly help. Here is one that I recommend:

Locate Your Vehicles A/C Low-Pressure Port

How to Find the Low-Pressure A/C Port on Your Car - AC Pro

Every car with an A/C system will have both a high side and a low side to the pressurized system. To locate your Low-Pressure port, check your manual, look online, or open your hood and look for aluminum lines like in the above photo. Take note that the larger tube is the low-pressure line, and the smaller tube is the high-pressure line.

Sometimes they have an "L" and "H" on them, to help you determine the proper one. If they don't have a letter indicator, don't worry, just find the larger of the two lines with a cap on it.

You also won't have to worry about connecting to the wrong one by accident, as the low and high-pressure ports are different sizes, and the low-pressure connector, won't fit on the high-pressure port.

Check Your Systems Pressure

AC Pro Car Air Conditioner R134A Refrigerant, AC Recharge Kit Includes Gas, Gauge and Hose, 20 Oz, ACP200-6 | Pricepulse

A little trick that I use to prevent losing money on a recharge kit if it wasn't needed, is to not remove the shipping disc from the recharge kit before testing the system. The shipping disc is a plastic dis that separates the can and the dispenser, and can only be removed by unscrewing the dispenser, do not do this yet.

This means you can take the recharge kit back to where you bought it from if your system doesn't need to be charged. To check the pressure of your A/C system, we are going to remove any packaging from the A/C can, except the shipping disc, and we are going to attach the end of the hose to the low-pressure port. Here is how we will check the A/C system's pressure:

A/C System Pressure Check Steps
  1. Remove packaging from A/C pro recharge kit (Except shipping disc)
  2. Connect the end of the hose to a low-pressure service port
  3. Ensure the vehicle is running, A/C is on, the fan is maxed out, and temperature is set as cold as it can go
  4. Inspect the gauge on the dispenser (Note: some dispensers have you turn a dial to reference proper pressure based on outside temperature, always read directions)
  5. If the needle is in the white (Low), then your system needs a recharge. Continue to Charge your vehicles A/C system
  6. If the needle is in the green (Filled), yellow, or red, stop, disconnect the A/C pro hose, put the service port cap back to Read on.

If the pressure is in yellow or red, your system is already charged, and there is a problem deeper in your A/C system, especially if your A/C compressor is not engaging. At this point, trying to check or service other things requires the knowledge of a skilled mechanic, to prevent harmful Freon from escaping into the atmosphere.

Charge Your Vehicles A/C System

AC Pro Refrigerant Recharge Kit Review - Horsepower Hub

At this point, we have determined your fuses are fine, and your compressor either is, or is not engaging. We have also determined that your vehicle's A/C system is low on refrigerant, and therefore also pressure. Now we can go ahead and charge the A/C system. This is super easy to do, so let's get right into it.

A/C System Recharge Steps
  1. Unscrew the Freon bottle from the dispenser
  2. Shake the Freon bottle vigorously for about 1-2 minutes
  3. Remove the shipping disc
  4. Screw the Freon bottle back on to the dispenser, you might hear a little hiss as the Freon bottle is punctured and freon moves into the dispenser
  5. Verify the gauge reading
  6. Fully squeeze the trigger while turning the can back and forth between upright and sideways, don't squeeze for too long, as you don't want to risk overfilling the system. I suggest 3-second intervals.
  7. Let off the trigger and check the pressure gauge. Note that you do not need to get the needle to the top of the green, once it is in the green your good
  8. Repeat steps 6-7 as needed to fill

Keep in mind that you can use the thermostat during this process to see if the temperature starts dropping during and after recharge.If your A/C is still no blowing code after following this guide, it is time to take your vehicle to a service professional, tell them what you have already tried, and make sure to tell them your findings during your testing and checking, it can help them come to a conclusion faster.

Final Thoughts

At this point, you know how to find and check the fuses for your A/C system, how to check compressor operation, and how to check and recharge your A/C system. Keep in mind if you recharge your system, and it starts losing its cooling ability after a few weeks, months, years, you might have a leak.

Due to the nature of Freon, you should get this checked out, however, if you are on a tight budget, and it needing to be charged every year, you might instead opt to just recharge it as needed. Want more information? Need a video?

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