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  1. #1

    wrong RPM on AC condenser fan

    The fan motor went out on my AC compressor. Had the repairman come out and replace it. My old motor was a 1075 RPM. Since he did not have an exact replacement he used a universal replacement motor. Unbeknownst to me the universal motor was only 850 RPM. What if any problems will this cause me as far as reliability and performance issues? I have searched the web and have found lots of information about going from lower to higher RPM but nothing about higher to lower RPM. Thank you for any and all advice.

  2. #2
    Join Date
    Dec 2002
    Location
    Houston,Tx.
    Posts
    16,115
    If a 1075 came out, a 1075 needs to go back in, like my dad use to tell me, they don't pay mfg. engineers six digit figures and up, for you to be out here altering the product. Basically it won't move as much air across the coil, and probably will increase the head pressure some.
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  3. #3
    Join Date
    Aug 2012
    Location
    Maine
    Posts
    180
    Quote Originally Posted by Mr Bill View Post
    If a 1075 came out, a 1075 needs to go back in, like my dad use to tell me, they don't pay mfg. engineers six digit figures and up, for you to be out here altering the product. Basically it won't move as much air across the coil, and probably will increase the head pressure some.
    X2, plus higher head pressure equals higher compression ratio equals an increase to your electric bill.

  4. #4
    Join Date
    Jun 2005
    Location
    SW Wisconsin
    Posts
    5,025
    It needs to be an exact (OEM) Original Equipment Mfg'er motor replacement.
    On a cross referenced universal motor replacement everything has to be the same including the amp-draw...

    The same goes for a condenser fan, it has to be IDENTICAL in every respect to the original fan.
    Also, the fan blades have to be mounted in the exact position to the venturi; that position should have been measured before removing an original fan.

    The venturi is the flared out portion of the fan deck, it's where the seal between the fan blades and the deck is formed. If the blade is not positioned correctly the air seal will "slip" causing the blades to flex up and down as the seal makes and breaks. This continuous flexing will eventually fatigue the blades to the point of cracking.

    In this case, the Service Tech will have to get that measurement information from the manufacturer, or measure another identical unit's fan position to the venturi. Some service manuals should have that information listed...

    Everything has to be performed RIGHT, or it may lead to problems...

  5. #5
    Join Date
    May 2008
    Location
    Central Fla.
    Posts
    311
    To add to what was stated above, the less air moved across the coil the less heat removed. The less heat removed it has to go somewhere and that would be back into the home. Guess what, it has to work longer and harder to do the same job. Get them back and do it right.Just my 2 cents.

  6. #6
    Thank you to those that took the time to reply. I called the repair shop and talked to the manager. He is sending somebody out tomorrow to fix the problem with the proper motor. I hope it's not the same guy that they sent before.

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