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  • whistling noise

    Hi
    I recently replaced a broken relais in the fan unit of my AC that
    switches the motor and the compressor on and off.
    The fan motor is a one phase three speed model. Since the replacement
    of the broken relais the unit developed a whistling noise at about 10 kHz.
    These oscillations are persistent at all speeds, so I don't think it is the motor
    itself. Does anybody have any idea what this could be (electric oscillations?),
    and could I stop them for example with adding a capacitor somewhere?
    This noise is very annoying and begins after approx. one minute after the fan has been turned on, so after the electric curcuitry has been warmed up.

    Thank's for any ideas.
    Chris
    chris w

  • #2
    any chance its the return air grills oscillating? Mine do and if you put your hand on them the noise stops, tighten the screws and it stops for a day or so, still searching for a more permanent solution

    Comment


    • #3
      Thank you for your reply. No I checked that. Even when I remove
      the air grill it is the same story.
      chris w

      Comment


      • #4
        pull the fan out of the furnace and see if the noise is coming from the fan unit or somewhere in the duct system

        Comment


        • #5
          I tracked down the source of the noise. If I run the fan only but
          with the airduct system in place, no noise, but as soon as I switch
          on the compressor and freon is pumped through the pipes, the noise
          starts. So I remember that freon was a little low and we replaced some.
          So it seems comming from the pipes, maybe pressure too high?
          I should probably dump some.
          chris w

          Comment


          • #6
            Don't know much about the A/C except that if the high side pressure is too high you will wear out your compressor quickly and if too low the condenser tends to freeze

            Comment


            • #7
              Originally posted by chris_wild
              I tracked down the source of the noise. If I run the fan only but
              with the airduct system in place, no noise, but as soon as I switch
              on the compressor and freon is pumped through the pipes, the noise
              starts. So I remember that freon was a little low and we replaced some.
              So it seems comming from the pipes, maybe pressure too high?
              I should probably dump some.
              To "dump some" refrigerant would be against the law. Put it in a old drum without the check valve.

              Very odd symptom, the moisture on the coil could be causing a slight pressure drop across the coil. This could all the door on the unit of whistle.

              In reference to return air registers making noise it sounds like the system could be undersized in the return air distribution. When air volume is increased above the rated amount registers will make noise. The temp drop across the cooling coil should be checked and if it is an electric furnace utilizing an amp meter (formula) determination of the cfm should be checked and compared to the BTU of the AC and the register/duct sizing of the system.

              Comment


              • #8
                Originally posted by chris_wild
                I tracked down the source of the noise. If I run the fan only but
                with the airduct system in place, no noise, but as soon as I switch
                on the compressor and freon is pumped through the pipes, the noise
                starts. So I remember that freon was a little low and we replaced some.
                So it seems comming from the pipes, maybe pressure too high?
                I should probably dump some.
                To "dump some" refrigerant would be against the law. Put it in a old drum without the check valve.

                Very odd symptom, the moisture on the coil could be causing a slight pressure drop across the coil. This could cause the door on the unit of whistle if you are at the upper end of the max negative static on the RA side. Also check the seal, if any or see if the door is bent or not tightened down adequately.

                In reference to return air registers making noise it sounds like the system could be undersized in the return air distribution. When air volume is increased above the rated amount registers will make noise. The temp drop across the cooling coil should be checked and if it is an electric furnace utilizing an amp meter (formula) determination of the cfm should be checked and compared to the BTU of the AC and the register/duct sizing of the system.

                Comment


                • #9
                  increas your return or change the grill making the noise to one the is less restrictive

                  Comment


                  • #10
                    Originally posted by chris_wild View Post
                    I tracked down the source of the noise. If I run the fan only but
                    with the airduct system in place, no noise, but as soon as I switch
                    on the compressor and freon is pumped through the pipes, the noise
                    starts. So I remember that freon was a little low and we replaced some.
                    So it seems comming from the pipes, maybe pressure too high?
                    I should probably dump some.
                    LOL, don't dump. epa won't like you so much. you need to balnce by super heat or subcool. subcool if you're using a txv, superheat if you're usin a fixed piston. this is the only way to balance the charge utilizing all temp and psi variables. the noise you're discribing more than likly is lo charge again. Good luck.

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