Air Conditioner Vacuum and Recharge Guide and Video

When you have made a repair to the air conditioner system of your vehicle and the system has been open moisture will get into the system, its unavoidable. After the unit is back together it must be vacuumed down which can be done with a simple vacuum pump and gauge set which are both available on Amazon for about $119.00 this set can be then used for all future system repairs and while helping family and friends.

If you would like to simply add rR134a refrigerant to your system, a recharge kit can be used for about $27.00. Learn more

As an air conditioner ages the compressor, condenser, evaporator core and hoses can leak or have mechanical failures which warrant replacement. I have created this guide for you so you can do the repairs yourself and save money while having the satisfaction of doing the job yourself.

These systems have a mixture of refrigerant and oil to keep the air conditioning compressor lubricated during operation. Measuring the amount of (pag) oil in the system is difficult because it's spread throughout the system, in other words if there is a major leak and oil is dripping out, the system will need a small amount of oil, unlike a very small leak which releases little to no oil, you must be the judge of this.

Most manufactures recommend the system to be vacuumed down each time you service the system to remove residual moisture which helps the compressor last longer. An a/c system may look a little different from manufacturer to manufacturer but follow the exact same principle.

It would be a good idea for you to know exactly how the system works so you know what I'm talking about when working on the system. Learn more

Check out the video below to see how the job is done and then continue reading below for tips and information you may have missed.

Each system has a specific amount of refrigerant needed to operate correctly and is located in the owners manual or on the system itself, this guide will successfully recharge the system even if this information is not available.

Tools and Supplies Needed

  • Air conditioner recharge gauge set and vacuum pump
  • R134a refrigerant
  • Protective eyewear and gloves
Before beginning, park the vehicle on a level surface with the engine off, apply the emergency brake with the transmission in park, wear protective eyewear and gloves.

Step 1

A fully charged system contains refrigerant under pressure (70 to 90 psi static - system not running), Allowing the refrigerant 134a to leak into the atmosphere is illegal though not harmful compared to it's predecessor r12, which was slowly bled out of the system by loosening a hose fitting at the gauge set.

This liquid/gas can be recovered if you have a recovery machine which most do not, this machine is mostly found in shops. Connect the gauge set to the low side charge port to check the start of charge before beginning work. If you choose locate a garage to have the refrigerant recovered before work begins. The recycling machine gathers refrigerant along with a small amount of compressor oil which is then is separated into individual tanks.

Low Side Pressure Connection

Step 2

A gauge set is needed to connect to the system on both high and low side pressure ports, and will also be used to vacuum down and recharge the system, inspect the connections to make sure they are tight to avoid leakage. These units must be "air tight" and not have any leaks at hose fittings or valves.

The red colored gauge and connector valve represents the high pressure side of the system, while the blue color represents the low pressure side. The center hose (yellow) is connected to the vacuum pump and then the new refrigerant supply bottle or can, both gauge valves should be closed before attaching them to the system.

Refrigerant Pressure Gauge Set

Step 3

Once the system is flat with no or little refrigerant present, begin the repair needed by replacing the failed or leaking component, begin by slowly removing the hose which connects to the component. As the final turns on the hose or fitting is undone you will hear a slight release of residual refrigerant which is normal, this means you are good to move forward in the repair such as replacing the compressor of the system. Learn more

Complete list of items that now can be replaced
  • High or low pressure hoses
  • Expansion valve or orifice tube
  • Compressor
  • Condenser
  • Evaporator core

Step 4

Now that the failed component has been replaced you are now ready to vacuum down the system, identify the service ports which the low side you should already know. The high side port should be on the line between the condenser and the expansion valve or orifice tube, remove the service port cap.

High/Low Side Pressure Service Ports

Step 5

While pulling the connector retainer ring upwards, press the valve over the service port, repeat this process for both ports. High and low side fittings will only work on their respective ports only due to size constraints this is to avoid confusion. Once secured, tighten the valve which activates the internal plunger that opens the service port valve to the refrigerant lines.

Tighten Valve

Step 6

Now observe both high and low side gauges with the valves closed, there should be little to no pressure in the system.

No Pressure

Step 7

Next, connect the center hose from the gauge set (yellow) to the vacuum pump, after reading the operation instructions for the pump, turn the pump on, this step is used to remove any moisture and static air from inside the system.

Connect Hose

Step 8

Slowly open the low side gauge valve, the pump will now start pulling vacuum throughout the system as the gauge needle slowly moves downward.

Opening Low Side Gauge Valve

Step 9

Once the vacuum pump has been on for 30 minutes, close the low side valve, the system should hold at 28-29 inches. Turn the vacuum pump off, at this point if the system loses vacuum on the gauge there is a leak and must be rechecked. These system leaks ill probably be a faulty O ring seal installed during the installation or a loose hose on the valve set. If the system holds vacuum for 15 minuets proceed to the next step.

Holding @ 29 inches of Vacuum

Step 10

Next, disconnect the yellow hose from the vacuum pump and attach it to a new R134a refrigerant source which could be a keg (shown) or individual cans which are both available at the Amazon or the local parts store.

R134a Refrigerant

Step 11

After the hose is connected to the refrigerant source open the valve on the keg and turn the it over to allow the liquid chemical to be present at the valve which helps charge the system more rapidly. If you are using individual cans connect them to the hose and turn them over as well.

Open 134a Refrigerant Keg

Step 12

While the gauge valves are closed and once the refrigerant source has been opened, the gauges will respond with an equal readings on both high and low side letting you know the refrigerant is present and ready to be installed. This is static pressure which will vary depending on outside temperature, the warmer it is the higher the reading will be which is normal.

Static Pressure
Reference the image below to see how the refrigerant will flow once the low side gauge is opened.

Refrigerant Flow

Step 13

Next, start the engine and turn the system to the highest settings of coldness including the fan speed. This will help work the system to it's fullest which will help charge the system completely.

System On

Step 14

Once the engine is running and the system is switched on slowly open the low side (blue) valve (never open the valve completely) until the refrigerant starts to flow to the compressor which will turn the system on via the pressure sensor. When this happens low the gauge pressure will start to drop and will cycle on and off as the system low side pressure raises and then lowers, the high side pressure will steadily start to rise. It helps to use a garden hose and spray water over the condenser at the front of the vehicle to help keep the system cool which completes the charge.

Low Side Pressure Drop - High Side Pressure Rise

Step 15

Continue adding R134a until the gauges start to look like this and the system stops cycling. If both gauges are too high the system is overcharged or the cooling fan is not working. If high side pressure runs way up quickly, (300+) and the low side goes into a vacuum, the system has blockage such as a plugged expansion or orifice tube. If the compressor engages, and neither gauge pressures move (stay the same) the compressor has failed and needs replacement. Learn more

Typical Gauge Readings

Step 16

As these pressures rise monitor the temperature of outgoing line of the evaporator and air vents in the passenger compartment, both should be cold to the touch signaling the system is full. Do not install more refrigerant thinking it will make the system colder, if fact it will do the opposite and make the system warmer as it's unable to achieve the pressure drop needed inside the evaporator.

Monitor Outgoing Temperature

Step 17

Once the system is performing properly and producing cold air close the low side gauge valve. If the system is not working basic troubleshooting is needed. Learn more

Close Low Side Gauge Valve

Step 18

After you have completed the charge, turn the ignition switch off and the system will shut down along with the engine.

Turn Key Off

Step 19

With the engine off, turn the high side connector counterclockwise to close the internal valve and release the plunger effectively disconnecting from the service port, repeat this procedure for both high and low side valves.

Loosen Valve

Step 20

Firmly grasp the valve retainer and pull up, this will release the connector from the service port. You will get a slight pressure lease sound when this is done which is normal, repeat this procedure for both valves.

Release Valve

Step 21

Once both valves have been removed, reinstall the dust cap for each service port. Once the job is complete, close the refrigerant supply valve and store the gauge set properly for the next repair. Enjoy the cold air!

Reinstall Dust Caps
If you have any question about the information above please visit our forum where thousands of question about this subject have been previously answered. Learn more

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