From: John De Armond
Subject: Re: Air Conditioner Woes...Update
Date: Thu, 08 Jun 2000 01:03:53 EDT
Message-ID: <393F2938.150DD7B0@bellsouth.net>
Newsgroups: rec.outdoors.rv-travel

Ops wrote:
 
> Here's a follow up to our request for help on our A/C unit.  As y'all
> suggested, I upgraded the existing 12 guage extention to a 10 guage (30
> amp) cord and then
> proceeded to turn the unit on... Nothing!!  Fan runs fine but still no
> air-conditioning.
> Bummer!!  Any other suggestions for items to check before I yank her out
> and take
> to RV repair center??  The unit is a '91 13,500 BTU Emerson "Quite Cool"
> w/heat
> strip.

If there's no evidence of high current draw (lights dimming - NOT 12
volt lights!, funny growling/humming noises, etc) when you turn it
on, then it is likely that the thermal overload compressor protector
has failed.  You indicated that you let it attempt to start for
quite some time on the small cord.  This means that the thermal
overload had to operate every minute or so over an extended period
of time.  The little boogers can't take more than a few dozen cycles
before failure.

To check, take the cover off the AC and find where the wires enter
the compressor.  there'll be a bakelite lid held on with spring
clips.  Pop those loose and remove the cover.  You'll see the three
wires going into the compressor housing and right beside it will be
a round bakelite device about an inch in diameter.  Usually labeled
with the Klixon brand.  The common lead of the compressor will go
through this device.  If it's not physically burned up, check it
with an ohmmeter.  Should get continuity between the terminals.  If
not, replace it.  Cost is cheap - $10-15 retail.  Be sure to get the
exact replacement.  These things are designed to have similar
thermal characteristics as the motor windings and are matched to the
compressor model.  A wide range of Klixons look alike.  The part
number printed on the top tells the story.

If you do have continuity, then you have to look elsewhere.  While
you have the lid off the compressor, check it out.  Put one lead on
the common wire going into the compressor. This is the one that goes
through the Klixon and is usually black.  Measure the ohms to the
other two terminals.  One terminal should have about 1/2 to 1/3 the
resistance of the other.  The higher resistance is the start
winding.  For a compressor of this size, the value will be in the
2-10 ohm range.  If one is open or zero ohms, bye bye compressor. 
Next check to ground from all three terminals.  Any continuity and
bye bye compressor.

If you've gotten this far with no obvious problem, hook one side of
your meter to ground and set it to AC volts.  Have someone turn the
unit on.  Check the two compressor terminals for voltage.  Should be
near 120 volts.  Check the compressor common.  Should be near
ground.  If you have voltage on the common, check the other side of
the Klixon.  If there is voltage across the klixon, then it is
failing under load.  If you have voltage on the compressor terminals
and it isn't running, probably new compressor time.  Note that if
the thing is locked up or the starting device is bad (cap, relay or
both), the klixon will open fairly rapidly so you have to make your
measurements fast.

If you don't have full voltage, then it's time to work backwards. 
the power switch is a good place to look, as is the thermostat.  On
my coleman, the thermostat is very rugged but the power switch looks
quite flimsy.  I'd look at it first.  Tracing it all out with your
ohmmeter is quite straightforward.