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Blower pulley sizes ?

 Is there a chart or formula to select correct blower pulley size?

 The complaint was not enough air flow. The A/C guy installed a new condenser and said the problem was the furnace (my problem now, the oil guy). When I got there I think his evaporator was frozen. The TX valve was a block of ice and I think the condensate drain my have been froze. I shut it off and let it thaw for a half hour and it started to drain and work again.

The air flow is barely noticeable at the registers. This is an early 1950's house so duct is probably inadequate but it always worked.

The furnace is a 26-27 year old Williamson low boy, belt drive. 1725 1/3 hp motor. Approximate 6-1/2"blower pulley and 3-1/4" ? motor pulley. It is a 5 ton condenser . I think the motor is too small, but I am a boiler guy. The furnace is 156,000 and 1.35gph.

Would Williamson have a chart or guide? I am going to search.


  • bill nye_3
    bill nye_3 Member Posts: 307

    So, I searched this site and found some math and if I understand at all I am spinning the blower at about 934 rpm. Not so fast huh?

    If I put a 5" pulley (driven sheave) on the blower I would get 1,121 rpm ? Would I want to do that ? Should I upsize to a 1/2 hp motor ?

    signed clueless in Ct.
  • RJ_4
    RJ_4 Member Posts: 484
    sizing RPM          

    contact the unit manufact, and get a fan curve, which will assist you on the correct rpm for cfm needed.
  • RJ_4
    RJ_4 Member Posts: 484

    Well I typed in this site and obviously I typed something wrong,  just look up pulley sizing on yahoo or culver motor, sorry for the confusion
  • bill nye_3
    bill nye_3 Member Posts: 307

    Thanks RJ, I went to my Sid Harvey branch and they called Williamson tech line. I bought a 3/4hp motor and recommended pulleys and belt. I will know shortly if it works, going there right now.
  • Techman
    Techman Member Posts: 2,144
    edited July 2013
    new motor

    be careful of the old wire size and circuit breaker/fuse and on/off switch's with that bigger motor.

    That AC guy should have handled HIS frozen evap coil in a more professional way,for sure! Good job to you !

    Upon startup someone knew something was wrong  and should not have allowed that compressor to be run and damaged! damaged!!
  • bill nye_3
    bill nye_3 Member Posts: 307
    worked out good

    The furnace had 12 ga. wire.  I tuned the pulley (ok sheave) with the door shut and got about 8amps. The label said 12.2 max.

    It is much more quiet and the air is noticeable at the registers. The TX valve kept icing up. The liquid line filter was about 6 or 7" ahead of the TX. My friend Scott told me the filter was probably restricted because the liquid line was warm before the filter and ice cold just after. I told the A/C guy and I think he changed it and trimmed his charge. I went back at 6PM it was about 94° outside and it was cooling the house and I think the customer was happy.

     The factory rep guy from Williamson prescribed all the parts right down to the belt size. Went together well. My only hitch was I had to swap rotation, took about two minutes more. I like it when a plan works out.
This discussion has been closed.