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pressure/vacuum test on old BM23

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  • pressure/vacuum test on old BM23

    I have a quandary.....My old BM23 is out of freon charge after a "re-fit" about 3 years ago, suspect high side port Shrader valve (it felt loose and could be tightened). When hooked up to gauges, it will keep a "test" pressure of 50 psi (not tried higher yet) for 72 hours plus with no change, but will not hold a vacuum for more than a few minutes, both tests done with the same set up, with both the hi /lo side manifold valves locked out (all hoses still connected to the vac pump and the hi/lo ports). Do I have a leak in the system, or are my various hoses and connections just not suitable for vacuum sealing?
    Any input would be appreciated.

  • #2
    50 psi will not necessarily tell you much. If you can, hit it with about 300 psi of dry nitrogen & watch your gauges for a while. If you don't see the needle move, take off your gauges to remove them as a possibility. You can leak check weld joints, fittings, etc. with a soap solution.

    Nitrogen, with smaller molecules, will leak out more readily than refrigerant or just plain air. Try the 72 hour test with the higher pressure & quickly put your gauges back on to see what you get. You should see a little drop from before just from removing & attaching your hoses but if the pressure is way down then you know you have a leak in your system & not your gauges/hoses.

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