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How to determine motor direction

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  • How to determine motor direction

    I have a blower motor on my central AC. It is a dual shaft motor. How do I determine if the motor rotates clock wise or counter clock wise?

    The motor has a label perpendicular to the motor shaft. If I needed to guess, the motor end, below the label, would be the front of the motor.
    Then facing the front of the motor and the shaft would be the point to determine shat rotation. Is this correct???

    I hope this is not a CCW motor.

    Jim
    So much to learn, so little time

  • #2
    Dual shaft? then one side is CCW and the other CW! Connect the power to it and you'll know...

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    • #3
      When you say label, do you mean arrow label? If so this is usually situated near one end?
      Also the 'driving' or 'load' end is usually the farthest from the termination end.
      And CW/CCW would be viewed looking into the end of the shaft.
      Is this a new motor or existing, in-situ?
      Max.

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      • #4
        This is the central AC unit at our summer home on the Mississippi. It is a mobile home type AC. Even though the unit is 40 years old it cools great.
        Not cheap to run though but for a weekend place it has done the job. Last few weekends the AC has been tripping the circuit breaker. We reset the breaker and the AC may run a couple of days then trip the breaker again.

        I thought replacing the fan motor could be something I could do myself. I have no experience tinkering with AC beyond basic electricity.

        I need to place an ammeter on the wires to see what is pulling all the current, the fan or the compressor. Not sure if I have one here at the river.

        I guess if the motor is dual shaft it would be both CW and CCW depending on orientation.

        I found a clamp on ammeter. The blower pulls 17 amps at startup then drops to about 4.4 amps. Fan is rated for 5.2.
        Next I checked the compressor. At start up the compressor pulled 10 amps and I thought no problem. Then the compressor kicked in and the current jumped to 20 amps and remained there. The circuit breaker is 25 amps so it is about maxed out. I'm not sure if the wire I checked was for the compressor or the entire system. Wow,,,,that's 4400 watts per hour. It never was cheap to run.

        Should I replace the circuit breaker?
        Jim
        Last edited by outback; 07-06-2013, 12:20 PM.
        So much to learn, so little time

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        • #5
          Fan motor likely 1/3 to 1/2 HP, or 3 to 5 amps at 110V. Compressor will be 3-5x this at least, maybe more even if 220v. For manufactured home, will be under 4T rating. Compressor
          is more likely to be the problem, but fan is cheap to replace. Dual shaft implies
          squirrel cage type blower.
          Steve

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          • #6
            20 amps on a 25 amp breaker is right on the limit. unless it's a special breaker rated for continuous use (and the wiring is upsized accordingly) , it's only designed for 80% continuous of max rating. I'm betting you have a compressor or other problem.

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            • #7
              Fan motor is 3/4hp 230 V. It could be the start up current if the fan trips the breaker. Current could increase after several cycles during the day.
              The entire unit is running on borrowed time. I'll bet a replacement unit won't last 40 years.

              I think I can buy a new blower motor for about $85. Is it possible to replace the compressor?

              The AC always starts up in the late morning. About 4:00PM the breaker trips.

              Jim
              So much to learn, so little time

              Comment


              • #8
                If the circuit breaker is old, as they age they do get easier to trip, in my experience.

                Also, it it may be a thermal type, and since you use the AC when it is hot out, that would just exacerbate the problem.

                I'd pop in a new breaker before spending money n anything else.

                Comment


                • #9
                  Originally posted by outback View Post
                  Is it possible to replace the compressor?

                  Jim
                  Not without a recharge and recovery set.
                  You have to recover the old refrigerant now due to environmental laws.
                  Max.

                  Comment


                  • #10
                    Im no AC expect, but I wonder what happens to there power consumption when you get low on gas?
                    Might increase and start tripping the breaker.

                    But yea, if the breaker has triped a few times, they have been known to get 'easier' to trip.

                    PS: those squirrel cage fans have confusing blades, they actualy face 'forward' into the wind (looks like it should be 'sucking' the air into the center), and the fan will blow air out (towards the exhaust on the radial) reguardless what way the motor spins, but much more air if it spins the correct way.

                    The centrafugal action overpowers the blade angle and the forward curve of the blades actualy helps move *more* air (at low pressures). Just watch the fan as it spins down after its been powered.
                    Play Brutal Nature, Black Moons free to play highly realistic voxel sandbox game.

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                    • #11
                      Originally posted by Black_Moons View Post
                      Im no AC expect, but I wonder what happens to there power consumption when you get low on gas?
                      .
                      Normally current goes down.
                      In most provinces here, you need a licence to work on A.C.
                      The latest systems run around 400lb/sq-in now.
                      Max
                      Last edited by MaxHeadRoom; 07-06-2013, 03:43 PM.

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                      • #12
                        If there's a squirrel cage fan on the motor, it should run in a direction which the arc on the blades face. If they don't have an arc, then assume that the arc is the side of the blade facing more towards the outside than the inside.

                        Or you can blow shop air outwards from inside the cage and note which way the cage wants to turn. This is the way it should be spun by the motor.
                        I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

                        Comment


                        • #13
                          Originally posted by darryl View Post
                          If there's a squirrel cage fan on the motor, it should run in a direction which the arc on the blades face. If they don't have an arc, then assume that the arc is the side of the blade facing more towards the outside than the inside.

                          Or you can blow shop air outwards from inside the cage and note which way the cage wants to turn. This is the way it should be spun by the motor.
                          http://cr4.globalspec.com/PostImages...2C7F52366B.bmp
                          HVAC fans have 'forward curved' blades for high velocity at low pressure.
                          Play Brutal Nature, Black Moons free to play highly realistic voxel sandbox game.

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                          • #14
                            Jim, I have to ask, have you gave the condenser coils a through cleaning? If not it could just be excessive head pressure in the heat of the day.
                            James

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                            • #15
                              A very common problem with older model cage fans is bearings loading up and getting stiff. The seals are no longer tight (if there were ever any seals,) the lubricant gets hard, they load up with dust and just generally get tired.

                              Pops

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