Xref: utzoo unix-pc.general:362 comp.sys.att:2515
Path: utzoo!utgpu!water!watmath!uunet!umbc3!motteler
From: motteler@umbc3.UMD.EDU (Howard E. Motteler)
Newsgroups: unix-pc.general,comp.sys.att
Subject: Re: Fan reversal on 3b1/7300
Summary: I tried it
Keywords: I've got this idea... (again..)
Message-ID: <804@umbc3.UMD.EDU>
Date: 19 Feb 88 08:38:57 GMT
References: <409@flatline.UUCP>
Organization: Univ of Maryland Baltimore County
Lines: 34

In article <409@flatline.UUCP>, erict@flatline.UUCP (eric townsend) writes:
> 
> Problem:  I live in an old, dusty house ... [much dust ommitted]
> Solution (of a sort):  Reverse the fan and add a easily removeable filter.
> Anybody tried this (and know an easy way to do it including Radio
> Shack part #'s :-) ) / see any problems with doing this?

A scrap of pantyhose stretched and taped over an intake grill makes an
adequate filter for coarser types of particles, cat hair, etc.  I ran
an old kaypro II with an added fan and this sort of filter for years.
Every month or so you need to clean it off or just throw it away.  The
advantage is very little air resistance and cheapness.  The
disadvantage is that it doesn't stop the finer particles or smoke.
(You can zap these with an ionizer, but don't set it too near your
crt, or all those micron sized particles will migrate to your nice,
positive screen.)

I played around with reversing the fan in my 3b1.  Just pop the fan(s)
out and flip it (them) to face the other way, and tape your "filter"
over the grille(s).  The power supply will run quite cool with the fan
breathing on it, but the front of the motherboard warms up a bit.
I ran this way for a couple of weeks with no ill effects, but finally
switched back.

You get less overall cooling when you do this.  Gas cools when it
expands, and warms when it is compressed.  In suction mode, air
expands and cools when it is sucked through little holes into the box,
while if you reverse the fan, you are compressing and warming air.
This effect may not have been the sole cause of the exess warming of
the mother board (warm air wants to rise, and you will be blowing it
down, etc.), but reduced cooling was noticable.  I changed back
after I got tired of warm air blowing over my fingers.

						Howard Motteler