fan?

[dig_dougpt]

I just picked up a new place and they said they just had their fan moter replaced with a stronger moter. Now it is not sucking like it used to. Was wondering if it could be to strong for their make up air (which is not working properly). so the fan is trying to pull more air than there is in the kitchen so it is really not sucking at all could this be the problem

[Hummerbk]

If I had to quess I'd say the belt is slipping or the wrong size pully was installed.

Its been along time since I studied fan theory but as I recall, a fan will move a fixed volume of air as long as the input or the output of the fan is not restricted. Choke off either one and the fan continues to spin at the same speed but the volume of air will decrease as will the amperage that the fan motor draws.
If you totally block air entering or exiting the fan, the fan will 'stall'. It will still be spinning but because it is doing no work it will draw minimal current.
I doubt that the fan is starting to stall because of a poor make up air system but is is possible. I would think it would pull air from the kitchen or dining room.
Do you hear air rushing noises around doors or does it even pull the doors closed in the kitchen? That might indicate a makeup air problem.
I would put an amp meter on the fan motor and adjust the pully size to where the fan draws its rated current. Thats where it has the potential to draw the most air.

[HotShot]

sounds like an air balance problem...or some idiot forgot to put an access door back on, or if it's a utility type fan, maybe they forgot to put the lid back on the duct. Or, it could be something like the belt isn't tight enough...

[Dave O]

Very common problem with motor install

The installer does not wire the new motor proper and the motor then spins the wrong way.

It will feel like it is exhausting but it is not enough

Check the rotation of the motor

Most have the arrow in the housing of fan to which way it should spin.

If you dont see that then you need to look at the fan blades themself to see which way the should spin from the top. Not the bottom with the power at breaker off.

What phase motor is it this sometimes is wrong and then they wire it for lower when it needs 220 and will not get up to full speed.

[Douglas Hicks]

If the fan motor is stronger, it may mean the fan is turning faster. Faster does not always mean more air movement. Each fan is designed to move a certain amount of air, CFM. Usually 10% faster or slower is still in the design range. More than 10% faster or slower does not move more air. Try the suggestions previously listed.

[dig_dougpt]

thank you guys I will forward all the info to them

[Tmrrptr]

Hot shot or dave O could have it right...

bigger motor will still be at 1800 or 3600rpm.
Must be same rpm as what it replaces or fan will cavitate.

Something is missing in the problem description....