X 1/9 AC systems

["Damon R. Kane" <X19Fan@domain.elided>]

Dan,

You asked why a heater valve could affect the AC?  The water pump is driven
off of the engine crankshaft.  The higher the engine revs, the faster the
impeller in the pump spins.  Since the heater circut is not isolated from
the pump by the thermostat (that's why you get heat faster than the engine
warms up in the winter) that means that the waterpump is pressurizing the
heater circut regardless of whether you intend to use it or not.  To keep
unwanted heat from the passenger compartment, even the cars without AC had
a valve to interrupt the water flow to the heater core.  I quickly realized
that my heater valve was my culpret as at idle, I got reasonably cool air
out of the center vents.  As I raised the RPM the air warmed to the point
it was hot on one side of the vents and barely cool on the other side.  The
AC could only partially overcome the heat load of the hot water leaking
internally through the heater valve into the heater core.  I pinched off
the heater hose in the engine compartment and found the problem eased a
bit.

As I mentioned in my previous post, the brass sealed valve was both on my
doaner car and all the spares I have in my stock as well as friends cars I
have inspected.  Jim Manbeck, another FLU member and a former Fiat dealer
technician rememebered the heater valve well when I first questioned him
about it a few years ago.  Actually he only ever seen the plastic valve. 
He insisted that with contortions it could be disassembled in place and the
O-ring replaced.  I really couldn't reconcile what the hell he was talking
about as all I had seen was the brass valve.  I ordered a new valve from
Fiat and was sent what was obviously a generic valve that could be
disassembled and refitted to the part of the valve that remained on the
car.  I can't describe how this works any better...cause I've never seen a
fully assembled in-situ plastic valve (one of life's little mysteries).

Now I really respect Jim a great deal and wanted to resolve my quandry.  So
I pulled a spare evaporator box complete with brass valve attached out of
my parts stash and dragged it along to a club event to show JIm.  I also
took along the useless partial plastic valve I just purcased as well.  As
he knew this was a hot topic for me, he also brought along a used partial
plastic valve (with a new O-ring) installed thinking this would solve my
problems.  When we met, he assured me that he had never seen a brass valve
before.  I was a bit surprised as I figured he had seen it all during the
heyday of these cars in the hands of non-entheuasisits.  It is no great
surprise to me that Fiat and Bertone changed parts.  Hell there is ample
evidence that they switched parts on a daily basis.  Some of the things
I've seen on similar vintage european cars would make your head spin, but
that's a story for another day.  The funny thing is I've seen  the brass
valve appearing in cars as late as '87's and as early as '79's.  The part
number on the microfiche is unchanged from even the earliest 74 AC cars. 
Obviously they Fiat  thinks the parts are interchangeable.  Without a
complete assembly I can't sort it out.

As we looked at the parts we had brought, it was evident that the used part
Jim brought me matched the replacment part I bought from Fiat. So evidently
the plastic valve must fit on some cars.  When the plastic valve is held up
to  the heater box that I brought it was equally evident that the geometry
was all wrong.  No way the valve could mount to the bracket on my heater
box (for the brass valve) and still connect to the hoses and cable and
work.  Still to this day I am thoroughly stumped.  Maybe someday I'll lay
hands on a beater parts car and see my holy grail... a plastic valve in
situ properly connected to hoses and cables!

 At this point in my quest,  I'm stumped.  I tried to find  a universal
cable operated valve at the local NAPA store that I could use in place  of
my internally leaky brass  valve.  No luck, all too big.  Out of
despiration and to help out a friend who had the identical problem I bought
a simple in-line heater hose valve from the NAPA store.  They have 2 or 3
sizes and configurations but only one will minimally offset the heater hose
when installed.  For my friend, I installed the valve in the heaer hose
that runs horizontally from the front of the footwell backwards towards the
front of the dash just below the dasboard  and above the console on the
passenger footwell.  He was a happy camper.  If he got cold, he would just
reach over and around the console and open the valve.

I'm loath to screw up the interior of my car.  Call me a fanatic for
originality.  I preferred to install the valve in the engine compartment 
at the heater hose that is mounted to the passenger side shock tower.  Not
as easy to use, but I figure, if I ever do solve the problem, I can more
ivisibly make the repair to the hose in the engine compartment.

As for the bubbles in your sight glass, if there is a steady stream of
bubbles, that is a sure sign of a low charge.  Some intermettent bubbles
are normal when the compressor kicks in.

One more tidbit, and one that I have not used... Jim told me that some
customers complained of poor AC cooling and he would simply disconnect the
electrical connectons on the anti-frost valve.  This is an electrical
solinoid valve. It  is mounted below the air cleaner on the fuel injected
cars.  Unlike most other AC systems in cars, where the compressor cycles on
and off according to the demand of the system (it's actually controlled by
a small thermostat right next to the expansion vavle), Fiat chose to take a
different route.  On the X 1/9 the compressor runs all of the time when you
are in AC mode.  To prevent the evaporator box from icing solid, there is a
valve that throttles the freon flow to a trickle.  This anti-frost valve
equates to de-energizing the clutch on a conventinonal system.  I'm not too
sure why they chose this convoluted system... my best guess is this
approach was to reduce the cycling of the load on the engine.  Or possibly
it was just a simpler way to control the AC.  Who knows.  

Since I am also posting this to the Digest, if anyone has any advice about 
or access to a complete evaporator box with a plastic valve installed, I
love to hear from you.

Ever frustruated with my AC

Damon