Testing the Leak Rate on Your Micron Gauge Itself

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As a technician gains skill they will learn that regularly testing your tools is a huge part of success. It isn’t long in the field before techs find out that just because a meter or gauge gives a particular reading it doesn’t ALWAYS mean it is correct. Vacuum is one of these areas.

Everything in an air conditioning and refrigeration system leaks to some extent, our job isn’t to eliminate all leaks, our job is is to reduce the leakage rate to as low as possible. When using a sensitive micron gauge we find that isolating an assembly and checking the “decay” or standing leak rate is a great way to test and ensure that a system has minimal leaks and moisture. The challenge is that all of the connections in your rig leak and even the vacuum gauge itself leaks.

Some techs attempt to test the leak rate on micron gauge by connecting it to a core tool and then straight to the pump, evacuating the gauge down to very low level and then valving off. If you do this, you will find that every commercially available vacuum (micron) gauge shoots up pretty quickly. This is because the VOLUME of the gauge and coupler are so low that ANY leakage whatsoever has an enormous effect.

In this video Ulises Palacios shows us how to use an an empty recovery tank to better test the leak rate of a vacuum gauge rig.

It is certainly important to test all of your vacuum rig components, just remember that volume makes a huge difference when decay (standing vacuum) leak testing.

— Bryan


  1. Avatar Daniel says:

    You brought up such a good point about how just because a gauge is giving a certain reading doesn’t necessarily mean it’s right. I agree that you should know how to check it to make sure nothing negative happens as a result. If your gauge does end up having an issue it would make a lot of sense to me to find a repair service that specializes in something like that. A precise instrument requires precise care, in my opinion.

    1. Hey Buddy, You need to find mentors to help you. They can be at supply houses, factory reps, guys you work with. Just remember everyone has their own misconceptions. On your existing question: using Nylog on your fittings. Using a dedicated set of vacuum hoses (clean, no oil) goes along way to eliminate problems. As far as fixing the internal vacuum gauge–good luck. just buy a new one at Trutechtools use getschooled for 8% discount.

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