Serious negative pressure.

[hvaclmnop]

I've had this client for about six months and last week was the first time I noticed that I can feel steady airflow coming down all the flues( 1 waterheater, 2 furnaces). They had gotten new hood exausts last winter and must have been snookered into buying some oversized ones. Last week I had a exaust hood motor go belly up. I replaced it and the new one is running high on amps. Belt tension is ok, everything is lubed, wheel spins freely. They do have the hoods cleaned regularly, but I don't understand why one is running high and the one next to it isn't. The one running high is in the corner of the kitchen; the other is by the door. Would that make a differernce? Larger make up air is pretty much my only option here, right?

[doc havoc]

How about decreasing adjustable sheave to slow the fans down a bit?

[ezone]

check rotation cage doesn't always turn in direction that looks right forcing motor to work harder than sized. burned out one b4. check w/amp meter you'll see difference and it will still draw

[hvaclmnop]

Originally posted by doc havoc
How about decreasing adjustable sheave to slow the fans down a bit?

BINGO!

Thanks, Doc, for shaking loose some cobwebs! The sheave was closed all the way. I opened 'er up and adjusted the tention and she runs nice and pretty about one amp under RLA.
A couple of years ago I got into a heated discussion with my boss about changing the speed on blowers. He believed that a longer belt slows the blower and wouldn't hear anthing else. I had to drive 20 miles to get an inch longer belt. He and his customer paid for it. He was aggravating in the way that since I was "tech school" and not "union hall" trained, I knew nothing, and what I did know was wrong. He even forbade me from coming to this forum. Needless to say, I don't work there anymore.
All that to say this...I never made the connection with blower speed to motor amps before; makes all kind of sense but I just had never been there yet.
Thanks to all; I actually did have the motor wired for the wrong rotation at first and she shot straight up to 50 amps.WHOA HORSEY!!I knew I came here for a reason.
Next question: Think I could change pulleys on the make up air blowers to speed them up and help my negative pressure or is that something I should even mess with? These people aren't in a big hurry. They haven't had any prep cooks fall asleep at the stove yet, but I sure don't like all those combustion gasses coming into the kitchen, That's got to get bad when it gets cold and they button the place up.

[nickellhead]

you can increase the sheave size as long as you watch the amp draw

[hvaclmnop]

Originally posted by nickellhead
you can increase the sheave size as long as you watch the amp draw

Could I increase motor size then, or do I max out on volume capacity of the blower? Well, first things, first; I'll try increasing the sheave. I think one of them may not be adjustable, though.

[superfittertech]

(2) limitations. (1) if make up air is direct fired you'll have to modify the profile plates. (2) if is not direct fired, depending on the blower size you maybe at max cfm depending on the fan curve. meaning increasing blower rpm may not increase cfm. We need more info model # blower, pulley, & motor size.

[isitfixedyet]

.06 neg. is perfect right?
and why?