From: John De Armond
Newsgroups: rec.outdoors.rv-travel
Subject: Re: Swamp Cooler
Date: Sat, 07 Oct 2000 20:52:38 -0400

R L wrote:

> Since this group seems to have the smartest people I've met on the
> internet I'd like to pose my problem and ask a few questions.
>
> Background;  I've recently relocated to the CA desert.  Here we cool
> homes (houses and RV's) with evaporative coolers, commonly called "swamp
> coolers."  These things are fairly simple devices.  A pump pours water
> over a medium.  A motor drives a squirrel cage fan to suck air through
> the wet medium and blow it into the residence.  Windows or vents must be
> open to allow air to escape.
>
> Now, my medium became clogged.  This was first noticed by a "swampy
> smell."  When I didn't pay attention to the smell the next indication
> was the 15 amp circuit breaker opening, recycled a few times with the
> hope it was a transient.  OK fine, I cleaned the medium and the whole
> unit.  Now my motor will only drive the fan for 2 minutes before the
> breaker opens.

A squirrel cage fan draws less current when its flow is blocked.
Therefore clogged media would not directly harm the motor.
However.  Most of fan motors are designated "air over" which means
they have to have a healthy flow of air over the case in order to
stay cool.  Most likely the motor overheated enough to cause winding
failure and a high resistance short that "shortens" up as it gets
hot.  Complete failure is just around the corner.  If the motor
starts willingly, that will be the problem.  If it drags slowly up
to speed, then it is worn out bearings.  Fan duty blower motors are
generally too cheap to spend the labor replacing the bearings - just
buy a new one.  Less than $100 retail.

If you're really cheap and want to join the SMS club AND you get to
the motor NOW before you try to start it again, you can try
disassembling it (careful, the internal wires will be brittle from
heat) and saturating it with red glyptol dielectric paint.
Available from electrical supply companies and some hotrod shops
(used to coat the inside of engine blocks)  It is available in both
aerosol and regular cans.  I'd recommend getting the regular stuff
in a can, diluting it about 2:1 and then pouring it into the
windings.  Allow it to soak in and repeat until they won't take any
more.  Glyptol works best if baked.  A couple of hours at 250 in the
oven (stinks) will do the trick.  If the insulation hasn't degraded
enough that wires touch at room temperature, this might bail you
out.  If you buy glyptol at an electric motor shop, see if you can
get them to megger the stator after you paint it.  If it meggers
good at room temperature, it should be OK for awhile.

Belt tension isn't all that critical.  But once the belt surface is
glazed from slipping, no amount of tightening will make it not
slip.  Probably not your problem here, though.  I tend to leave fan
belts a bit on the loose side to be a bit easier on the el-cheapo
bearings in the motor.  I highly recommend changing the belt when
you work on the motor.

>
> From the manual, belt tension is important.  I've gone from loose to
> tight.  I don't have a tensiometer to measure 3/4" deflection at 3 lbs,
> I think that is fairly loose.

> Is there a simple way to test to see if the starter relay remains
> engaged?

Probably doesn't use a relay.  Usually a centrifugal switch on the
end of the rotor that cuts out the start winding as the motor comes
up to speed.  You can hear it click in and out.  Many fan motors
don't use a switch at all and instead use a run capacitor that stays
in the circuit all the time.  If the cap goes bad the motor either
will not start or will start slowly and draw a lot of current.  Cap
failure is fairly common.  They're cheap - under $10 retail - so
it's easy to just change one out and see what happens.  If the
electric motor shop or appliance parts warehouse doesn't have the
exact size, it is safe to go the next larger capacity cap.  The
voltage rating must be the same or higher.  Don't be alarmed if the
replacement cap is physically much smaller than the old one - the
advances in miniaturization are slowly creeping into the electric
motor world.

If for some odd reason it does have a start relay, you can hear it
operate.  You can also see it operate on a clamp-on ammeter.  The
motor will draw a large current until the motor comes up to speed,
the relay then disengages and the motor draws a much lower run
current.  The sound of the motor changes too, when the relay
disengages.  If it does not disengage, the motor will sound labored
and may not come all the way up to speed.

John