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Airco HF help needed please.

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  • Airco HF help needed please.

    First of all, I'm new to the site and very happy to have a source for some great info on this old airco I was given.

    Airco 3A/DDR-224HPA/B-D Serial # HH098855

    Pure tungsten
    100% argon

    The High Frequently doesn't seem to be functioning at all. It's a scratch start and once started doesn't exactly weld. (Picture attached).

    Basically I am having the same issues as this post.

    I have followed the path that is discussed there and and while I was troubleshooting found my spark gap insulator backboard was broken. I replaced the spark gap and I am having the same issues.

    All of the capacitors show good via a multimeter but I have not purchased a capacitance meter to check them with (I would use it for this project and doubtful ever again).

    With the lights off I don't see any leakage, just the spark gap firing.

    If I understand the post I have been following correctly, replacing the pfc capacitors are what fixed his problem. That being said I can't seem to find them anywhere.

    Any help here is appreciated. Thanks, Nick

  • #2
    The "PFC" capacitors are power factor correction capacitors that just help reduce the effective load on the power from the wall that powers the unit. Essentially, they have nothing to really do with the weld output and only affect the input current load into the machine.

    If you see sparks between the spark gap, that is the biggest challenge. Then it is matter of are you losing the HF due to issues such as coiled up TIG torch lead, is it water cooled and your coolant is not the correct kind (non-conductive), connection by the output studs is too close to the frame of the welder and the HF is grounding there and not making it to the torch.... on and on.... Basically, it is tracking down all the items in the secondary weld loop that could be preventing you from seeing the HF at the torch.

    That all being said, if you are welding on steel, then that can be DC and if you scratch start, you don't need the HF. If you are welding on aluminum, then you do need the HF all the time as this is a sine wave based AC welder and you need the HF to keep the arc stable.


    • #3
      Blue_tech, thank you for the reply.

      I do see the spark between the gaps, my tig torch is a brand new setup that is uncoiled and the fluid is brand new as well. I flushed and verified the flow in the system before I put my new torch setup on.

      I am trying to weld aluminum, AC continuous high frequency (how the machine is setup for this particular issue). That being said, the DC functionality on steel seems to work just fine.



      • #4
        I would like to know if you are familiar with this machine or not, meaning, is it new to you or has this machine been working flawlessly in your shop for some time? I ask that because there are several levers, knobs and switches that must be in the correct position in order for your machine to operate as you’re demanding it to.


        • #5
          I am fairly familiar with the setup. It was functioning at the plant I worked at several years ago, that being said the reason they gave it to me is the HF stopped working. I'm set in AC, continuous switch on, Tig (blade switch inside cabinet), remote amperage control on, remote contractor control on. I spoke with a Miller tech the other day and he walked me through some troubleshooting but I might be fighting a losing battle here.


          • #6
            This really should be a solvable problem. As BlueTech said, if you have sparks at the gap, something is pulling down the HF between the spark gap and the torch. I have never had hands-on with one of these machines, but have worked with a lot of high voltage, high frequency stuff. First thing I would try is get the machine in a completely dark room, put on HF continuous, and see if you see any leaking HF anywhere. Just follow the path from the secondary of the HF transformer all the way to the gun.


            • #7
              Thanks Aeronca41, I have done exactly what you suggested. I didn't find any leakage anywhere. The Miller tech also thought I had a leak to ground somewhere so I ran through that process with ALL of the covers off the machine. I ended up selling the machine to a friend this afternoon though so it's no longer my issue. I really appreciate all the help and insight from you guys though. Sincerely-Nick