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Evacuation of new A/C Units

on top of all that TGO said, the service valves are more then likely shut and if you turn on the compressor you will seriously damage it in about 10 minutes


  • CB_3
    CB_3 Member Posts: 1
    Evacuation of new A/C Units

    A contractor installed a hot air and A/C system in my house, however he was waiting for a friend to come evacuate / charge the A/C system. The friend has never shown up and the contractor is telling me the A/C units come with enough charge that it will not matter. There are two towers (I believe one is a 2 ton and one a 3 ton). Is it safe to turn these on? Will it damage the A/C units, or is worst case that I don't get as much cooling power as I should?

  • TGO_54
    TGO_54 Member Posts: 327
    System start up

    The units need to first be pressure tested for leaks, then evacuated to below 500 microns, then you have to check for moisture to be sure the evacuation is complete. After that you have to do a start up that includes checking pressures, tempratures, and verifying proper air flow and balance.

    Anything less will effect the performance of the system and could damage the equiptmant.

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  • Empire_2
    Empire_2 Member Posts: 2,343
    All are correct.

    The unit should be disabled until the service tec. gets there. I never leave a condenser ready to fire inadvertently until the start up can be done. You can probably turn on the fan though for air circulation.

    Mike T.
  • Eugene Silberstein
    Eugene Silberstein Member Posts: 1,380
    Some very important items

    All of what was posted by others is absolutely correct and I would like to take this opportunity to stress to all the importance of PROPER system evacuation and charging.

    - Most condensing units come precharged with enough refrigerant for the entire system (indoor coil, outdoor coil, compressor and interconnecting piping) provided that the length of the refrigerant lines are EXACTLY the length that the system was charged at the factory for. This length is typically as high as 25 feet and as low as 15 feet. If the actual length of the refrigerant lines is longer than that provided for, refrigerant will have to be added to the system when the system is put into operation. If the actual length of the refrigerant lines is shorter than that provided for, refrigerant will have to be removed from the system.

    - Therefore, the ONLY time the factory charge will be perfect is when the refrigerant line set length is equal to the length provided for at the fatory.

    - Leak checking the system is very important PRIOR to releasing the refrigerant into the system. Systems should be leak checked with an inert gas such as nitrogen and checked for leaks using a soap bubble solution. NEVER pull a vacuum to leak check. Many old timers do this, but it is poor field practice. There are instances where leaks in the system will not show up. A perfect vacuum is, for arguments sake, -15 psi. when pressurizing a system for leak checking, systems are typically pressurized to 125 psig. In addition, pulling a vacuum on the system can cause particualtes to be pulled into the system at the point of a leak, temporarily sealing it. When the sytsem is then pressurized with refrigerant, the leak surfaces.

    - Make certain to remove the nitrogen from the system and perform a thorough evacuation procedure. None of this "20 minutes on the pump is fine" stuff. It's not. The larger the system, the more evacuation time is needed.

    - During the evacuation process, close off the valves on your gauge manifold periodically to check on the status of the process. If the micron gauge reading rises and stops at some point in the vacuum range, there are still "nasties" in the system. Continue evacuating. If the micron gauge reading rises and continues to atomspheric pressure, you have a leak. Your evacuation is complete when the system reaches AND HOLDS a vacuum that is lower than 500 microns.

    - Replace the oil on your vacuum pump BEFORE each use. You will speed the evacuation time on the system and your pump will last longer.

    - GET ALL OF THE AIR OUT OF THE SYSTEM. Air contains moisture. Moisture will react with the refrigerant and the oil to create acid in the system. Acid will eat away the insulation on your compressor motor windings as well as eat away at the interior surfaces of the refrigerant piping.

    - When starting up your systems, make certain you have the proper airflow through both the indoor and outdoor coils BEFORE adjusting the refrigerant charge. Make certain the air filters are in place as well as all of the service pansels on the air handler and condensing unit.

    - MAKE SUPERHEAT AND SUBCOOLING CALCULATIONS. How can you determine how full (or empty) your heat transfer surfaces (evapoartor and condenser coils) are if you don't do this?

    I know this is getting back to basics, but a very good friend told me, "Knowing WHY is often better than knowing HOW".
  • rucomfy
    rucomfy Member Posts: 43
    Can you really....

    effectively pull a suitable vacuum through a gauge set ???

    I stopped that nonsense (or what I perceive to be nonsense)
    eons ago. How do you mitigate the porous nature of the hoses and or the manifold itself ??

    If you could please enlighten me I would be very interested in your suggestions. THank you.
  • knowing why...........


    He who knows why
    shall be master of
    he who knows how .

    Ken Resnick
    He who knows WHY

    Shall be master of

    He who knows HOW
  • Eugene Silberstein
    Eugene Silberstein Member Posts: 1,380
    Great Point!

    I do recommend installing gauges on a system during the evacuation process, as this makes the charging process much easier and reduces the chances of introducing air to the system when adding them later on.

    What I also recommend is to use short lengths of flared 1/4 inch copper tubing instead of the hoses that come with the gauge manifold.

    Thanks for the post!
  • Eugene Silberstein
    Eugene Silberstein Member Posts: 1,380
    If it isn't

    Well... If it isn't the very wise friend himself!
  • Techman
    Techman Member Posts: 2,144
    Evacuation hoses

    I have a set of BLACK hoses which I was sold as "not pouris" and an "evacuation manifold" that has 2 ,1/4 " hoses and a center hose that is 3/8" that goes to the vacuum pump and a 4th hose that goes to freon drum,and I hook up the micron instrument somewhere away from the hoses. I use this set for 15 tons and smaller . Then for large systems I have a real beauty,of 2,3/8 copper braided flexible hoses and a center hose of 1/2 copper braided flexible hose.
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