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Lochinvar Fan Speed Troubleshooting

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Rizz861
Rizz861 Member Posts: 64
in Gas Heating
So far when I’ve seen a fan speed error on any lochinvar it’s always been the fan. Venting is always usually good (proper install and has bird screens) wire harnesses are always plugged in. No loose connections. Fuse is always good (come to think of it I’ve yet to see a blown fuse be an issue yet). So what id like to know is how to properly check voltage to diagnose it. They are usually dead on arrival with that error, but today I had one that worked but gave me the error. I know one of the last things is the control board, so I’d like to be able to rule that out. I know one day I’m gonna slap a fan in there and be wrong so I’d like to avoid that. It looks like lochinvar makes a tester. Do you really need this thing or are there some things you can look for with your meter? Thanks!!

Comments

  • Ryno
    Ryno Member Posts: 1

    It operates w a pwm signal. check to see if there is 10 to 42 vdc at terminal block s5 blk and white wires during start up. If so, likely the motor. Or you can buy one of the lochinvar motor test tools for about $250.00..

  • Jamie Hall
    Jamie Hall Member Posts: 27,237

    Oh dear. Well, if it's a PWM signal, you can also use an oscilloscope or oscilloscope attachment for a laptop like this

    Pico Technology PicoScope 2204A-D2 Digital Oscilloscope 2 Channels 10 MHz, 8 kS, 2000wfms/s, Handheld Portable USB PC Lab Scope Waveform Generator, PS7 Software: Amazon.com: Industrial & Scientific

    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • mattmia2
    mattmia2 Member Posts: 16,462

    i was thinking the varicac and unregulated wall wart and a tachometer route

  • 109A_5
    109A_5 Member Posts: 3,882

    Looks like the tool grabs control power from the system to power itself and also passes it along to the fan control board. Then when the test button is pressed it commands the fan to one or more RPMs and the RPM is verified within a tolerance and probably within a time limit.

    You may be able to verify the control power to the fan with a meter and there are some very inexpensive handheld scopes getting more popular in automotive troubleshooting and for electronic hobbyists. So you could monitor the command PWM and the RPM monitor circuit. With a bit of reverse engineering and practice you could get good at it.

    If you do a lot of this type of thing the test box will probably save a bunch of time and give better Pass / Fail results quickly.

    Apparently the test tool works on Lochinvar and others.

    image.png image.png
    National - U.S. Gas Boiler 45+ Years Old
    Steam 300 SQ. FT. - EDR 347
    One Pipe System
  • HomerJSmith
    HomerJSmith Member Posts: 2,774
    edited February 3

    The fan has two plugs. the rear smaller plug will tell you if the fan is ok. Unplug the rear plug while the boiler is operating and the fan will run to high rpms. If it does, than the fan is good. If not, the fan is bad and need to be replaced. The series # on the boiler label is important in choosing a replacement fan.

    Why is it, nobody ever tells us the model # and size of the boiler the poster wants help on. Oh, well, "C'est la Vie".

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