How To Pull Vacuum On Car Ac – The DIY Process

Have you got in your car and switched on your AC system only to receive warm air from the vents? It is unnerving and frustrating, right? Trapped air or moisture causes such malfunction in the system. Therefore it is important to evacuate trapped air in the air conditioning system. So, to protect your air conditioning system from breakdown, you need to vacuum the AC system.

Trapped air in the system affects not only the efficiency of the cooling system but also causes premature breakdown. For this reason, this article will discuss reasons for pulling a vacuum and how to pull a vacuum on a car AC system.

What Is The Purpose Of Pulling A Vacuum

Here are the reasons you should vacuum your AC systems;

how long to vacuum car ac system

Eliminate unwanted contaminants

Do you have to pull a vacuum on a car AC? It is essential to pull a vacuum on the air conditioning system, especially after replacing a faulty AC compressor or condenser. The purpose of vacuuming an air conditioning system is to remove unwanted contaminants from the system.

Keep the system in a clean environment

Pulling vacuum from the air conditioning system involves evacuating moisture and air from air conditioning and refrigeration systems. Pulling a vacuum from an AC system is done to eliminate harsh substances from the system. And to ensure the system runs in a clean environment.

To prevent system premature breakdown

If you ignore to vacuum your AC system, it may lead to a mechanical breakdown on the compressor and expansion valves. Other issues it’ll project include refrigerant line restrictions, lower efficiency, premature corrosion, and ultimate system failure.

To save your air conditioning system from the outlined issues above, you need to vacuum the system regularly. Most especially during system refrigerant recharge after installing a new AC component.

Step By Step Guide On How To Pull Vacuum On Car AC System

Let’s look at simplified steps on how to pull a vacuum on a car AC system before determining how long to vacuum a car AC system.

As alluded above, if you fail to pull a vacuum from an air conditioning system, it’ll reduce the performance. I recommend pulling a vacuum on your AC system periodically.

Do not wait until problems creep in. Let’s unveil all the DIY procedures you need to pull vacuum from the AC system.

how to remove air from ac system without vacuum pump

Getting started and locating low and high service ports

Park your vehicle on a flat floor in your garage or driveway. If you want to vacuum the AC on the driveway, check your local law to avoid violations. Do not start the car yet or turn on the AC.

Put on your protective glasses and your working gloves. Locate the low and high service lines.

The high service port has an H inscription on it and the low service port has an L inscription. Locate the refrigerant lines. They are attached to the compressor and track the service ports on them. Don’t worry about displacing them. They are not interchangeable. Proceed to the next step.

Hook up the manifold gauge

After locating the service ports, the next step is to hold up a gauge set. You need a manifold gauge to connect both low and high service ports to the system. You’ll also use it to vacuum and recharge the system.

Ensure the connections are ‘air tight’ and there are no leaks on the hose and fittings. You need to ensure the valves on the gauge are in closed positions.

The blue hose represents the low-pressure side while the red hose represents the high-pressure side.

The middle yellow hose should connect to the car AC vacuum pump and it’s where you’re going to recharge the system later on. Close the gauge valves before connecting them to the air conditioning system.

Connect the gauges to the systems

The next step is to determine how much vacuum to pull on auto AC system. Connect the blue gauge to the low-pressure service port. To fix it, push down the knob and snap the hose on the service port and let go. Wiggle the hose and see if it snapped incorrectly.

Get the red hose from the manifold gauge and snap it on the high-pressure service port. Follow the same step on the low-pressure line to do it correctly.

Unlock the gauge manifold hose on both the low-pressure and high-pressure hose. Inspect the gauge on the manifold gauge. It should be on ‘0’, meaning there’s no air in the system. Next, take the yellow line and connect it to the car AC vacuum pump.

You don’t have to tighten the hose more than hand tight. You need nothing like a plier to do the job for you. There’s a seal there that’ll do the job. Hand-tighten other hose connections.

If there’s any refrigerant in your AC system, make sure you go to a nearby garage and recycle it. You don’t have to violate your local laws by discharging Freon into the atmosphere. These refrigerants cause harsh effects on the atmosphere. So, you should be environmentally responsible.

Cross-check the blue, red, and yellow lines and ensure they are properly connected and opened up. If you’re concerned about how to vacuum an AC system without pumps, it’s possible, but you’ll get a poor result. Let’s proceed to the next step.

The Vacuuming Action

Turn on the vacuum pump. Check the gauge on the manifold gauge. It should be in the ‘0’ position. Open the valves on the blue and red sides of the gauge. The gauge needle should come down below the zero position. The blue gauge should creep down to 30 inches, which is where you want it to be.

After letting the pump run for about 30 minutes, close the red and blue valves on the manifold gauges and let them sit for about an hour. This step is to determine if there’s a leak in the system.

If the gauge needle in the blue stays at 30 after the waiting period, it shows there’s no leak in the system. Once you determine there’s no leak, continue the vacuuming for 45 minutes. Switch on the vacuum pump and open up the gauge valves.

This is going to vacuum all the air and moisture in the system until it’s nice and dry inside. You can get busy with something else and let the pump do its job.

After 45 minutes and everything looks pretty good, turn off the valves on the gauge and switch off the vacuum pump. 

You’re done with the vacuuming process. The next step is to recharge the air conditioning with the recommended refrigerant.


Q: How long should you pull a vacuum on a car AC system?

Now that we know how to pull a vacuum on car AC, how long does it take to pull a vacuum from a car AC system? It takes an average of 45minutes to 1hour to pull a vacuum from an AC if there’s no leak in the system. This is enough time to expel moisture and air out of the system.

When vacuuming deep moisture, consider replacing the AC receiver or accumulator. This will help to keep moisture under check.

Q: How do you get the air out of a car AC without a vacuum pump?

While the most general way of vacuuming the air out of an AC system is using vacuum pumps, you can still pull vacuum without a vacuum pump. Refrigeration and air conditioning systems function with refrigerant and oil circulating in them.

Any other substance is unwanted and should be expelled out of the system. Whether it’s oxides, moisture, debris, or air, you need to pull it out.

While using vacuum pumps is the best method for evacuating air from the air conditioning systems, there are other alternatives. The best alternative requires installing access valves on both low and high-pressure valves. Here are the steps to follow;

  • Install access valves on the refrigerant lines
  • Depress the high-pressure line access valve on the AC and observe the low-pressure line. Once the high-pressure access valve gets to the lowest point, close it and switch off the car.
  • Recharge the low-pressure side to about 10 PSI and ensure the pressure on both lines equalizes.
  • Repeat the first step.
  • Repeat steps 2 and 3.
  • Recharge the AC system.

Q: Can you pull a vacuum on just the low side?

Of course, you can pull vacuum from only the low-pressure line. The air conditioning system runs continuously. It has a component called the orifice tube, which restricts refrigerant flow but doesn’t stop it. Expelling vacuum from only the low side will still work.

Q: Does pulling a vacuum remove refrigerant?

Pulling vacuum from your cooling system removes refrigerants. However, only pull vacuum after recycling the refrigerant.

Using the vacuum pump to pull refrigerants will only damage the pump. They’re only designed to evacuate moisture. If you want to pull refrigerant with a vacuum pump, don’t do it. Instead, get a refrigerant recovery machine.

Q: Does vacuuming AC remove oil?

Vacuum pumps reduce the refrigerant pressure and cause it to change from liquid to gas state and expel out of the system. They are not designed to remove oil. In short, they can’t lift oil uphill or from the compressor.

Q: How much vacuum should an AC system hold?

An AC system needs a vacuum of about 500 microns or 29.92 hg gauge pressure to successfully remove any air, moisture, debris, or oxides that made their way into the system. An air conditioning system can hold 29.92 hg for a minute or more.

Final words

We’ve provided sufficient information on how to pull vacuum on a car AC and why you need to vacuum the AC system. With the above instructions, you can do this on your own.

After successfully vacuuming your AC system, pat yourself on the back. Wait! Do not forget to give us some credits. This has saved you an expensive service fee that you would have given to an HVAC technician.

Osuagwu Solomon

Osuagwu Solomon is a certified mechanic with over a decade of experience in the mechanic garage, and he has over five years of experience in the writing industry. He started writing automotive articles to share his garage experience with car enthusiasts and armature mechanics. If he is not in the garage fixing challenging mechanical problems, he is writing automotive repair guides, buyer’s guides, and car and tools comparisons.

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