# A/C Compressor Fan is "Pulsing"



## notmrjohn (Aug 20, 2012)

Sounds more like the fan blades are bent. They're easy to bend out of shape either in removal or installation, or while in operation, and you sed it has happening already. And bent blades could have caused those seals to go out. Out of balance due to mis-placed weights ( in both senses) would cause more of a vibration and shaking of the entire motor and what ever it is mounted to. Is there a vaguely funnel shaped shroud on the bottom of the outlet? Make sure the fan blades are up in it. If fan too low it creates a back pressure, fighting that pressure can create a 'pulsing' effect. Other systems just have a fan with smaller diameter than the opening. I'm assuming this fan blows out the top and the motor is mounted to the bottom of the top? Balancing and finding a bend and then fixing is just like you would do on a ceiling fan, only upside down. Take the top off, and with motor and fan connected lay it upside down on a flat surface. Mark the top at an outside corner of the fan, make all measurements from that point. Measure from the mark on the top to the leading corner of one of the blades. It's easier to just use a straight stick and mark the stick than deal with a bunch a lil marks on a ruler. Label your blades and marks 1 L(eading) etc. Keep the stick as verticle as possibleb ut if you put the same corner on mark and same edge to blade you'll be OK. Rotate the fan and check each leading and trailing corner. You could also check the center of outside edge of blades. You've just checked for twist in the blades. There may be adjustments or spacers at the hub, pro'lly not so you have to carefully twist the blades back into the same angle with each other. 
The blades could also be bent along their length, they are all at the same angle, but one is 'sagging'. Check that they are secure at hub, (I shoulda sed that in first place) Get off to the side, eye level with the fan and have sumbody give it a fast spin, watch for up and down and side to side 'wobble' ( and I shoulda sed do that B4 doing all that measuring) depending on how many blades, you may be able to lay a straight edge across blades. Make 4 or 5 marks along a line from the hub out and check the blades along it. Mebbee with care you can straighten them out. 
Now if you wanta check weight balance and trust your self safety wise, and can connect the motor, and can clamp or other wise secure the top across two supports, saw horses say, turn the fan on just long enough to get it to speed and see if it shakes, wobbles or pulses. You could do that upside down and right side up. Balancing the fan could be difficult, its like balancing tires, you need the proper tools or machine. A large HVAC supply house may be able to do it, but if you're gonna do that you may as well buy a new fan. Which you might do anyway.
Check the inside of unit for any shrouds that are out of place or anything else that could be confusing the air flow. I can't think of anything else.


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## beenthere (Oct 11, 2008)

look for cracks in the blades or blade brackets.


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## ChazzLav (Aug 24, 2012)

Great info. Your assumptions are correct on the layout. It's pretty much what I figured. I haven't had a chance to take it apart at see about straightening things yet (hurricane coming, -other worries first). I was thinking I would just get a new fan but I may try to adjust it first. The strange thing is that it started doing the pulsing BEFORE I took it apart to replace the motor. So I didn't bend anything, it happened all on it's own. Anyway, thanks for the help, I'll let you know what happens.


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