From: Phil Tong [ptong@sirius.com]
Sent: Thursday, June 15, 2000 1:30 PM
To: 928
Subject: [928] RE: shark a/c

(snip)
> sources of
> less than stellar performance are:
>
> 1) the recirculation flap (comb flap) is filthy from age and
> therefore not
> opening/closing completely.
>
> 2) the heater control valve is not closing completely due to age
> or lack of
> vacuum.
>
> My gut feel is that very minor vacuum leaks in the system combined with
> grime and dirt on the flap components prevent cooled air from
> making it in
> to the cabin without assault from outside fresh air and engine warmed air.
>
> fwiw

Good advice.  The only change I've made recently since installing the new
heater core valve was to clean the grit & fuzzballs out of the inside air
temp sensor.  Maybe that did the trick in this case.  Whenever the car is in
motion then a/c gets pretty chilly, there's just not enough airflow through
either condensor or evap. while idling static esp. in 90+ or in yesterday's
case 100+ temps.  Too bad I didn't stick the thermometer in the vents
yesterday to record output drats.  Now that I think about it too bad I even
forgot to turn on the rear a/c for most of the day (doh!).  Remembered later
and it cycled on/off just fine.

Phil been knocking on wood daily since...




From: Dr. Bob [dr.bobf@worldnet.att.net]
Sent: Wednesday, August 08, 2001 8:31 PM
To: 928
Subject: [928] Re: How Cold Is A Meat Locker??

> Sandy Bryant wrote to the list:
>
>
> > With all the posts regarding AC performance,conversions
> and repairs, I submitted my 87 S4 to the Porsche Dealer to "have it
> checked". Even though it was working, I have always wondered how cold should
> it be. I have had the car since 87 with no AC maintenacne. Some $600
> dollars later, a new hi pressure hose(I think it is new) and 2 pounds of Freon,
> it seems to work about as well as I took it in. Vent temperatures are
> subjectively no colder than before. I wish I had spent the money on 2 of
> the new wheels I want.
> >
> > SO. If anyone has a 928 Meat Locker, what kind of vent
> temps are you getting? How low should they go? Are they different for
> single or dual Air. Is there some way to objectively measure or compare?
> >
> > Sandy Bryant '87S4,5SP, Silber/Black
>
>
 Sandy:

 One of the first tools you will want is a good thermometer
 for making those objective measurements of the AC
 performance.  I found an inexpensive electronic model at the
 kitchen accessories department at a local store.  The one I
 have has an LCD display that reads down to tenths of a
 degree, and stores min and max temp readings along the way.
 Less than $20.  Anyway, poke the probe end into the center
 vent, drive with the AC on for a bit, then turn the
 thermometer on.  This way the min and max recordings will
 tell you somethings about your system.

 Making the assumption that your  system is functioning
 correctly, you should see a min temp between 35 and 40f, and
 a max temp between about 40 and maybe 45f. The test
 conditions include engine RPM greater than 2000, fan set on
 2, and the rear air not turned on at all.  If you see these
 temps, your system is working fine.

 Defining AC performance is very subjective without the
 thermometer.  Besides temperature, your body is quite
 sensitive to changes in humidity.  Let's say that the
 outside temp is 90 and RH is 70%.  When you get into the
 cooled car, you might "feel" some 10 degrees of system
 improvement just based on the change in humidity.  Add in
 the actual temperature drop and you'll guess that the AC
 system is more effective than similar temp conditions on a
 less humid day.  On the same note, the AC actually works
 harder on humid days since it has to extract enough heat out
 of the air to condense the moisture, then even more heat to
 get the air temp below the dew point.

 Your AC system has a freeze switch, a thermostatic switch
 that keeps the evaporator above the freezing point so that
 moisture it condenses stays as liquid.  If the evaporator is
 allowed to go below 32f on a humid day, it will soon be
 coated with ice, and eventually will no longer pass air. No
 matter how much extra cooling capacity your system has
 available, that freeze switch will keep the center vent
 temps high enough to prevent that icing.

 In my '89 S4, same AC configuration that is in your '87,
 converted to R-134a, I see center vent temps of 21f with the
 freeze switch not working.  Take a look at the factory
 service manuals, and compare the temp charts for the R-12
 system and the R-134a system used on the '93 and later cars.
 You can see that there is at least 10 degrees better
 performance from the R-134a in the later cars, and at
 ambient temps in the 90f range the R-134a actually extracts
 even more heat than you might expect.  This is due to better
 expansion valve performance, optimized for that critical
 heat range.  The graph shows R-134a temps as a max line,
 with a pretty large gray "range" area underneath.  A
 properly prepared R-134a system in the later cars will
 easily meet the performance shown on these graphs.  I
 strongly recommend that folks with underperforming R-12
 systems in later cars consider this conversion next time you
 need to "top up" your leaking system.

 Hope this helps with your question.  Your system may have
 been functioning at less than optimal levels before it was
 serviced, yet still had enough capacity to cycle the
 compressor on the freeze switch.  Pulling all the air out is
 part of the procedure, especially after the hose was
 replaced, and that will improve performance a bunch if there
 was much air in there to start with.  The shop put in (up
 to...) two pounds of R-12, plus the stuff they had
 previously extracted and cleaned (not very much) for a
 charge weight total of about 1050 grams (about 2.8 pounds)
 in a car with rear air.

 Sandy,  I've included a couple attachments, PDF files that
 show the temps you might expect from your R-12 system as
 well as those that the R-134a system useed in the later
 cars.  These are the manual page graphs referred to above.
 Listers will not see these as they are stripped off for our
 text-only list system, but can request copies by sending an
 e-mail to me with "Temp Article" in the subject line.

 dr bob





From: Mack McMurry [mailto:mcmurry@spawar.navy.mil]
Sent: Wednesday, April 17, 2002 4:19 PM
To: 928
Subject: [928] AC question-heat won't stop


John,
If the mech is right, there is a fix so cheap and easy you will fall off
your chair.  

My car's heat would also not shut off.  In the left fender, behind the head
light, in front of the wheel, there is a flexible air tube. (You have to
remove the mud shield in front of the tire to get to it.)  Inside that tube
is the outside air temperature sensor (looks like a little lipstick). Just
down the wires a little ways is a connector.  Pull that connector apart and
clean the two contacts.  The male pins are easy to clean, but the female
holes are a bit more difficult.  I pulled a couple of wires out of a wire
brush, bent them over and made kind of a little brush like you clean a gun
barrel with. Only a lot teenier.  Or figure out your own way to clean out
the female contact holes.  Then coat everything with silicon grease to keep
the contacts clean after you plug them back together.

That's all there is to it.  If this was the problem, like on mine (and many
others), your heater will come under YOUR control. Hope that's it!
--jer
83sat