A 7 Step-by-Step Process of How to Vacuum Mini Split Lines

If you have invested in a mini-split AC, you definitely want to know how to vacuum mini split lines.

Vacuuming is one of the most important mini-split maintenance activities. It removes the moisture and air that accumulate in a mini-split’s lines during operation.

When left unchecked, this combination can undermine performance, cause leaks in the coils, and even cease the system.

Thankfully, vacuuming a mini-split is a reasonably straightforward process, even for first-timers. This article covers the tools you need and the steps to take to vacuum down your mini-split air conditioner successfully.

What You Need To Vacuum Mini-split Lines

Vacuuming a mini-split air conditioner requires the right equipment. Below are the tools to gather before you begin.

  • Vacuum pump – pulls out the air and moisture in the mini-split lines to create a vacuum. 
  • HVAC gauges – measure pressure changes in the lines as the vacuum pump does its job.
  • Mini-split adapter 5/16 to 1/4 coupler – adapts the Blue hose of the HVAC gauges to the low-pressure port on the outside condenser.
  • Allen Keys – aid in loosening the pressure valves on the outside condenser to let the refrigerant into the system.

If you cannot borrow or rent out any of these tools, the online market has some decent low-cost varieties you can buy. 

Best Budget Vacuum Pump

ZENY 3.5CFM Single-Stage 5 Pa Rotary Vane Economy...
  • Inlet Port: 1/4" Flare, Warm note: 1)Pressure Scale:0~400psi, 0~140psi 2)Length of hose:1.2m Red:1/4''-1/4'' Yellow:1/4''-1/4'' Blue:1/4''-1/4'' Please make sure your manifold gauge is in accordance with this size. Any question in using, please contact seller first. *** A self-paying vacuum pump Adapter needed if inflet not suitable.
  • High Efficiency and Low Noise, Heavy-duty Aluminum Alloy Casing, Oil Drain Plug Positioned at Bottom of Oil Reservoir,Internal High Volume Cooling Fan for Extended U
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The ZENY 3.5CFM packs a strong punch for a sub-$70 vacuum pump. It can pull air pressure down to as low as 5 Pa or 37.5 microns, which is excellent for a single-stage vacuum pump at this price point.

Moreover, at 3.5 cubic feet per minute, the ZENY is more than fast enough for mini-split vacuuming.

Best Budget HVAC Gauge Set

ZENY Diagnostic A/C Manifold Gauge Set R134a...
  • Warm reminder: 1) Designed to meet 1/4" Standard SAE requirement for refrigerant permutation. 2) It's Celcius scale shown, NOT Fahrenheit scale. 3)Units are metric measurement **4) Numbers on the panel are not large enough, please wear glassed or take a closer look to read **5) Any questions or doubts of item or replacement, please contact seller in the first time for solution, and we'll do our best to help.
  • Each hoses is aprox 4ft ( 48 inches) each with 1/4" SAE fitting; Working pressure :500psi, Burst pressure :2500psi
  • Aluminum manifold body, Built in viewing glass
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The ZENY Manifold Gauge Set is highly recommended for beginners because of its straightforward setup. It comes with easy instructions right off the box.

Furthermore, because it is one of the most popular gauge sets on the market, you will not struggle to find videos on using it. 

Best Mini-split Adapter 5/16 to 1/4 Coupler

Wadoy R410a Adapter for Mini Split HVAC System...
  • ✅【GREAT REPLACEMENT】: R410a Adapter, Mini-Split, A/C Low-Loss Fitting. Converts the 5/16" SAE charging-Vacuum ports to 1/4" SAE gauge-hose set.
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  • ✅【PREMIUM QUALITY】: 1/4" Male x 5/16" Female Adapter. Made of 100% high quality brass , strong sealing for durability and safety. Access valves high tensile strength while resisting corrosion.
  • ✅【PERFECT FIT 】: With 45° angle on the service port site for easier access.Perfectly fits for R410a mini split system air conditioners,HVAC,and refrigeration service.

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The Wadoy R410a adapters offer a high-quality brass finish and excellent sealing for maximum safety and durability.

Best Entry-level Allen Key Set

EPAuto Allen Key Set Hex Key Wrench Set, 30-Pieces...
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  • 15 × Short Arm Metric: 10mm, 8mm, 7mm, 6mm, 5.5mm, 5mm, 4.5mm, 4mm, 3mm, 2.5mm, 2mm, 1.5mm, 1.27mm, 0.9mm, 0.7mm
  • Storage Case: Hinged cased opens flat allowing easy access to wrenches
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The EPAuto Allen Key Set comes with 30 different-sized high-quality Allen keys at a great price.

How to Vacuum Mini Split Lines  (Step-by-Step Process)

Now that you have gathered the tools required, it is time to tackle the task at hand. The following are the steps to take to vacuum your mini-split air conditioner lines. 

1. Check the gauge valves

An HVAC gauge set has two gauges: Red and Blue. The Red gauge is the high-pressure gauge. It is fed by a Red hose, which connects to the high-pressure line of an HVAC system.

Suction through this hose is controlled by a Red valve located at the side of the gauge. Because mini-splits do not have high-pressure lines, the Red hose does not connect anywhere when vacuuming.

As a result, the Red valve should always be off.  The Blue gauge of the HVAC set is the low-pressure gauge. It is fed by a Blue hose, which connects to the mini-split’s low-pressure line.

The Blue valve controls suction through this hose. You should always keep this valve shut unless the vacuum pump is working. 

You can shut both valves off by turning them clockwise and on by turning them anti-clockwise. Check here on how to use HVAC gauges.

2. Connect the gauges to the mini-split and pump

With both valves off, connect the Blue hose of the HVAC gauges to the low-pressure port on your mini-split’s outside condensing unit. This is usually the only port on the condenser.

Connect the Yellow hose of the HVAC gauges to the vacuum pump’s port. 

3. Turn on the vacuum pump

After connecting the hoses to their respective ports, confirm that all valves are shut and power on the vacuum pump. As the pump starts up, open the Blue valve on the HVAC gauges.

With this valve open, the pump will begin to suck the air out of the mini-split, and the Blue gauge will read negative pressure. Leave the pump to run for 20-30 minutes.

4. Turn off the vacuum pump and observe the gauges

After around half an hour, turn the vacuum pump off. Let the unit sit for another 30 minutes while observing the Blue gauge.

Any rise in pressure will indicate a leak along the line. In this case, you will need to check your connections and restart the vacuum pump. 

5. Shut off the Blue valve

The vacuum has held if the gauge maintains its negative reading 30 minutes after switching off the pump. You can turn off the Blue valve. 

6. Let the refrigerant into the mini-split

Using the appropriately sized Allen Key, loosen the refrigerant valve on the condenser to let the refrigerant into the system.

As the refrigerant goes in, turn to the HVAC gauges and fully open both the Red and Blue gauges. This step ensures the refrigerant travels throughout the system. 

Related Post: How to Charge a Window Air Conditioner Refrigerant

7. Disconnect the Blue hose from the unit

With the valves wide open, remove the Blue hose from the condenser as fast as possible. Some refrigerant will leak out of the hose, indicating that the vacuum has been maintained.

Find a way to reward yourself for a job well done.

Why Should You Vacuum a Mini-Split Air Conditioner?

The primary objective of pumping down a mini-split AC is to remove air and moisture from the lines before adding a refrigerant. Not vacuuming a mini-split can result in poor performance and, eventually, complete failure. 

Below are some common problems caused by air and moisture accumulation in mini-split lines.

Rust formation

The moisture in the condenser coils can promote rust development on key internal parts of the AC, such as the crankshaft, piston and piston rings, and even motor windings.

Lower cooling performance 

When air and moisture are left in the refrigerant coils, they occupy space meant for the refrigerant. A smaller refrigerant volume translates to reduced cooling capacity. 

Higher energy consumption

Air and moisture in the mini-split lines inhibit the flow of refrigerant in the mini-slit lines. As a result, the condenser works harder and consumes more energy to achieve and maintain the desired temperature. 

Wrapping Up

Mini-split air conditioners need vacuuming from time to time. If your air conditioner has been struggling to maintain its performance and efficiency, vacuuming it before charging refrigerant can help it recover. 

We hope you have found this guide on “how to vacuum mini split lines” useful and are now ready to vacuum your mini-split. Keep us updated on the progress in the comment section below.

Also, do not hesitate to share this article with your equally DIY-capable friends! 

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Jesse Pinkman is a passionate HVAC professional writer who grew up repairing any home appliance on which he could lay his hands. He is responsible for ensuring that every article we publish is SPOT ON. When he's not in the office, he enjoys hiking, watching football, and spending time with his family.