Ferrari Mailing List: 308 A/C work

[Rick Lindsay (rolindsay]

Hello Friends - especially those of you in North
America.  Spring is here and in Houston, it feels like
summer.  And as I waited in the heat of the garage, I
decided to go to work on my 308's failed A/C.

About 7 years ago, Ric Rainbolt converted my 308GTB's
A/C to use R134a refrigerant.  In seven years, the
pseudo-Freon had leaked out leaving the A/C just a
warm-air blower.  When Ric rebuilt the A/C he did it
right.  He had the compressor rebuilt, replaced the
receiver-drier and pulled a 1-bar vacuum on the system
until all the moisture had evaporated and was removed.
 As usual, Ric's work was text-book precise.

When I wrote to the List about a week or so ago, I
didn't know that Ric had the compressor rebuilt.  That
is the most likely component to fail in the A/C
system.  With it relatively freshly rebuilt, I decided
to just work the system today, as it exists.

Here's a look at the location of the compressor,
http://www.aubard.us/Ferrari/Access.JPG .  Under the
shroud in the spare tire compartment are the drier and
the pressure valves,
http://www.aubard.us/Ferrari/HPIM1038.JPG .  Here's a
top-view of the same area,
http://www.aubard.us/Ferrari/HPIM1040.JPG .  Further
forward is the condenser radiator.  You can see the
plumbing in this picture,
http://www.aubard.us/Ferrari/HPIM1041.JPG .

Once access to the compressor is gained, I could see
that Ric had properly changed the valves to accept
R134a hoses,
http://www.aubard.us/Ferrari/CompressorHead.JPG .  The
blue side is the low pressure side and the red is the
high pressure side.  This is further confirmed by the
word "SUCTION" stamped into the compressor head, next
to the blue side connector.

The gauge manifold hoses are attached to the
compressor, http://www.aubard.us/Ferrari/HPIM1049.JPG
.  The yellow hose is attached to the vacuum pump,
http://www.aubard.us/Ferrari/HPIM1047.JPG .  This
"pump" uses air pressure across a venturi to create
the vacuum.  90psi of air pressure will generate about
1 bar of vacuum or about -14.7psi.  Of course, that is
a complete vacuum and is virtually impossible except
for space-going Ferraris.

My compressor can make a lot of pressure but at the
air volume the "pump" requires, the most vacuum I can
generate is about -12psi.  With the pump connected to
the manifold, you can see the vacuum generated on the
blue-low-pressure side gauge.  This gauge also
functions as a vacuum gauge,
http://www.aubard.us/Ferrari/During_evacuation.JPG . 
Here you can see -12psi vacuum.  I let it hold at this
level for about an hour then disconnected for about a
half-hour to see that the vacuum held.  It did. 
Realistically, this vacuum should hold for 24 hours.

While the vacuum is desiccating the  the system, I
checked the electrical aspects of the A/C.  In the 308
there are two safety switches.  The low pressure
switch measures the low-side pressure and interrupts
the compressor clutch circuit when the low-pressure
side drops too low.  Here's what that switch looks
like, http://www.aubard.us/Ferrari/HPIM1039.JPG .  Its
location is obvious, being right next to the
receiver-drier.  Much harder to locate is the
high-pressure safety switch.  It is behind the brake
fluid reservoir,
http://www.aubard.us/Ferrari/HPIM1044.JPG .  Sorry
about the soft focus.  Here's a close-up,
http://www.aubard.us/Ferrari/HPIM1043.JPG .  The
high-pressure safety switch is in series with the
low-pressure switch.  Working together they protect
the compressor.

With the low-pressure switch disconnected, I applied
12v to the compressor clutch and verified that it
activated properly.

After achieving adequate vacuum, I added about 12oz of
R134a to the manifold via the yellow hose.  This is
done with the engine off, the high pressure hand-valve
off and the low pressure hand valve open to the yellow
hose.  While the refrigerant was flowing into the low
pressure side of the system I monitored the low
pressure safety switch with an ohmmeter.  At about
20psi on the gauge, at the compressor, the switch
closed.  When that happened, I disconnected all the
electrical test equipment and buttoned up the
connectors.

I ran the engine with the A/C on and added another
12oz of R134a.  The air from the evaporator blew cold.
 At run-time, the high side pressure was about 160psi
while the low side was about 30psi.  Once the second
can of refrigerant was in the system, I shut the car
off.  After about 10 minutes, the R134a leaked across
the valves and began to equalize the pressures,
http://www.aubard.us/Ferrari/After_shutdown.JPG . 
80psi now on the low-side, 135psi on the high-side.

About 15 minutes later, I took an hour-long drive with
cool air circulating around my person. :-)

Hope you enjoyed the story.

rick
PS: Notice I didn't say anything about being
eco-friendly.  Didn't have to.  The system, after 7
years, was down to atmospheric pressure.  No foul, no guilt.