How to evacuate and "pull" vacuum on an R134a car AC system

Proper way to "pull" a vacuum from a discharged auto AC system. This applies to the newer R134a refrigerant systems as well as the older R12 systems.

It is not only necessary, but critical that you evacuate your AC system IF it has been opened to the atmoshere. However, if you are just adding additional R134A Freon to your system, evacuation is not required.

Automotive A/C Vacuum Pumps are used to remove air and moisture from an A/C system that has been worked on. If, for example, the A/C system has been repaired(compressor, condensor, evaporator, accummulator,or whatever), this is when evacuation is required. During evacuation, the air is removed from the a/c system and at 28" pounds of vacuum, the moisture begins to boil. The moisture now becomes vapor and is drawn out of the system by the vacuum pump.

At the end of the evacuation, you have a system that is free of any air or moisture. If you do not evacuate your system prior to charge, it may work for awhile, but the moisture will eventually cause corrosion and other unwanted chemical reactions in your A/C system. This will shorten the operating life of your A/C system.

Category:

Autos & Vehicles

Tags:

• AC
• R134a
• vacuum
• pump
• air
• condition
• R12
• discharge
• high
• side
• low
• shrader
• valve
• car
• truck

[araki916]

when you're "pulling" the vacuum, is your car on or off? I know when you are recharging the r-134, you need to have the car running and the a/c on.

[mikecarter79]

@araki916 Vacumm = Engine Off , always.

[kjhhjhbcjdc]

wen u vacum everything out what should the gages say ?

[mikecarter79]

@kjhhjhbcjdc The needles on the gauge will go BELOW the 0psi mark, which tells you that your system is in a state of vacumm.

[kidcool1977]

can I rent this vacuum pump

[mikecarter79]

@kidcool1977 I am not sure. Check with Autozone or Advance Auto to see if they rent vacumm pumps.

[richwaldo]

Attaching an inline Torr gauge would help determine when the vac process is complete. Then if it doesnt pull down to under two Torr (uk regs) or doesnt maintain the vac when you shut the lines off and turn the vac pump off you know there might still be a leak.

[wangbungal]

if you have to vacuum the system,but the system still have decent amount of pressure,let say 25 psi at low side,and 115 psi at high, can you still use this pump? great vide by the way, im just wonderin what pressures your vehicle have before you vacuum it..

[Cobra281s]

@Moralvorstellung7 Both sides need to be vacuumed. Id imagine you could do it through one side but youd need a very powerful pump.

[Moralvorstellung7]

I thought you only needed to vacuum pump out on the low side. Are you telling us it needs to simultaneously be on the low AND high side as well, because not all of us have a manifold gauge set.

[aguswahyuni]

A/C Vacuum Pumps are used to remove air and moisture from an A/C system that has been worked on. If, for example, the A/C system has been repaired(compressor, condensor, evaporator, accummulator,or whatever), this is when evacuation is required. During evacuation, the air is removed from the AC system and of vacuum, the moisture begins to boil. The moisture now becomes vapor and is drawn out of the system by the vacuum pump.

[bethjean1015]

@araki916 when vacuuming the car is off. When charging the system the car needs to be running with the ac on MAX.

[dan110024]

@jlinn91 Yes... If you have pulled any of the lines off, you would have let air into the system. Air contains moisture. Moisture can/will lead to acid and corrosion of your system. Not to mention you would have lost your refrigerant in the process of releasing the lines.

[dan110024]

You that you've got this up for the DIY'ers out there... But don't you need licenses to purchase refrigerant? Things may be different here in Australia, but I'd be quite sure that America (assuming that's where you're from with your accent) requires it too?

[dan110024]

@mikecarter79 Manifold gauges hardly give an accurate vacuum reading. Best to use a vacustat for proper evacuation, and get down to around 500 microns.... but I know, plenty of people just use manifold gauges and monitor the vapour coming from the vacuum pump exhaust :)

[jlinn91]

will i have to vacuum the system if all i did was pull the lines off near the radiator??