[DMCForum] a/c tech issues
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[DMCForum] a/c tech issues



For those of you who like reading my long-winded technical experiences:

About 8 months ago I had a noisy a/c compressor.  It "clunked" when the
clutch engaged and it rattled as it pumped.  I took the system apart to
find
aluminum shavings spread through the system with water.  I get the
expansion
orifice out and find that the previous owner tried but failed.  When I got
it out, it was banana-shaped.  Because they couldn't get that connection
out
of the way, they didn't replace the accumulator either.  I cut it open to
find it was saturated with water.

I flush the system, install a rebuilt compressor, pull a vacuum.... pull a
vacuum... put some freon in it anyway, find a leak at the evaporator, pull
the damn thing out... .leave it out for 8 months.  I found out that the PO
in his unsuccessful attempt to remove the orifice managed to put deep
gouges
in the pipe with what looked like channel-lock teeth.  A nice flow of R-12
was coming through one of them.  I have a local a/c shop solder on new
pipes.  I didn't get a warm fuzzy feeling from the results, so I buy
another
evaporator from PJ Grady $480.  I thought this would be better than new.
Turned out it was copper.  This guarantees the system will be 8ºF less
efficient.  This is Florida.  So I install the repaired evaporator.

Now the fun got really interesting.  The damn expansion orifice wouldn't
fit.  The new pipe soldered on was too small.  Was I going to take it back
to the a/c shop?  Hell no.  I just put it in the dash for the last time.
So
I get my best set of drill bits out and make it larger.  It took three
bits
before I got something big enough for the orifice.  The last diameter I
used
was size "K".  Prefer metric sizes?  Hate fractions?  You'll love letter
sizes.  Anyway, I mopped out the shavings with oil-soaked Q-tips, pulled a
vacuum and charged her up.

It works great now.  I really have to listen for the compressor to cycle
where before there were so many metal chips gumming it up that the clutch
made a loud oil-can sound with each cycle.

I used an upgraded expansion orifice (variable orifice valve) in place of
the antique fixed orifice valve.  It works about the same when cruising
but
makes much more efficient use of the pump at lower speeds.  Instead of
dumping the flow through an orifice too big for the low pressure, the VOV
restricts accordingly chilling every last drop of freon and allowing the
compressor to cycle much less often.  The DeLoreans original design was
adequate.  The upgrade is highly recommended if converting to R-134a.
Being
used in a R-134a system should make it even better.  More testing will
tell.
I've only had it for 2 days now. :-)

While I had everything apart, I cleaned up the insides.  All the foam
seals
turned to goo just like a headliner backing.  What wasn't covered with goo
was rusted.  I sanded it all, painted with rust-sealing primer, painted
with
black high gloss, replaced old foam with auto/marine grade gasket from
local
hardware (closed cell), remove inadequate factory insulation (earlier cars
weren't even insulated), replaced with www.b-quiet.com L-comp so it is now
sound-proofed as well as insulated.  No more drips in the passenger foot
well.  Modified the defrost duct so that it shuts off when front vents are
on.  This took adding a vacuum actuator that operates a custom-made
throttle
plate pivoting in the duct.  All made from brass plate, rod & tube (hobby
store).  Now no more fogging the outside of the windshield at night.

I undid some idiocy the factory built into the system.  They put a
stainless
steel mesh screen on the evaporator.  In theory this seems good.  The
purpose of a screen is to keep stuff out of the evaporator.  So then why
did
they put the screen on the other side where it holds stuff IN the
evaporator?  I cut a circle of this screen to fit the air input to the box
and install.  I was slightly worried that the screen would be too
restrictive, but I notice no reduction in air flow.  This screen will keep
leaves out of the system.  I want the evaporator to last forever.  On a
later thought maybe they put the screen to build up air pressure passing
through the evaporator, but I've never heard of this before.  (I'm still
kinda green on a/c.  No really!)  There is a piece of plastic riveted in
restricting the airway anyway that looks adequate.  So I think the guys
just
put the screen on the wrong side.

There are photos of it in the first (and at present only) issue of
Gullwing
magazine. Well, I could go on for a few more thousand words, but you got
the
gist of it.   And as you can tell, I've been smoking some really good pot.

Walt


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