|Well here goes; FAQs on Air Conditioning in the
Porsche 911 Family:
1. Let's start with some
basic nomenclature (old Army word)
a. Evaporator; Box containing the coil of tubes and fins that
gets cold and a fan that moves that cold air towards you. An expansion valve at the inlet
of the coil meters the flow of refrigerant by measuring the temperature of the outlet
b. Compressor; Pump that draws the Freon (R-12 or r134A) from the
Evaporator that is now a low pressure Gas and compresses it to a high pressure Gas.
c. Condenser; A coil of tubes and fins set in a flat sequence
designed to release the heat that the freon has picked up in the Evaporator. This must be
placed in the air stream of the car or at least have a fan to cool it. To a point, you
can't have too much condenser.
d. Receiver/Drier; A small metal can or tank situated between the
Condenser and the Evaporator that does three things; stores extra freon, filters out
impurities, and removes moisture that may be in the system. Contains a desiccant (of many
different materials) which can trap only a small amount of moisture.
e. Hoses; Connect all the components together. Usually in three
sizes, #10- from the Evaporator to the Compressor, #8- from the Compressor to the
Condenser, and #6 from the Condenser to the Receiver/Drier to the Evaporator. Perhaps the
best investment a 911 owner can make would be to change to the new 'Barrier' hose which
resists this weeping of refrigerant.
f. Thermostat; The second switch on dash, this one has a small
hollow tube containing R-12, that senses the temperature of the Evaporator. coil and shuts
off the Compressor if it gets below a predetermined setting. After a half-hour of freeway
driving, this switch should be turned back a quarter turn to prevent the coil from icing
up, especially at lower blower speeds.
g. Blower Switch; Usually a three speed switch that controls the
Blower Speed and the Clutch on the Compressor too. When first you start up the car, switch
to high and open a window to flush the hot air out then turn the blower to a comfortable
level (refer to above).
h. Clutch: The electromagnetic connection between the belt and
the Compressor. A series of windings in the field are energized when the a/c is engaged
causing the hub (which is secured to the Compressor shaft) to be attracted to the pulley.
This is a metal to metal connection and will eventually wear out especially if allowed to
To 'AIR or not to 'Air...
Why the heck not ! Unless you use your car for a full timey racer, why not be as
comfortable in your Porsche as you are in your Rabbit ? This is a car you probably only
use in the summer anyway, why not enjoy it ?
Can it work?
When installed correctly and maintained adequately the a/c in your Porsche is as
efficient as any other car, and can be even more so !
What are the main Troubles?
Essentially the biggest problem is the way the car is laid out that causes the
Porsche to have 8 or 10 times more hose than a real car. The trouble being that a/c hose
has always been made to purposely leak through tiny pin holes along it's entire length.
Such a small amount as not to measured but nevertheless leaking. The new Barrier Hose
should eliminate this drawback. The other problem has to be that no manufacturer ever
seemed to have enough Condenser on the car for the Hottest Days.
What about winter storage?
While I can't guarantee it, I'm certain that if you use your a/c once a week or
two for just ten minutes you will maintain the moisture in the seal enough to ensure a
long life. So make a calendar, and each Sat go out and start the car, let it run for ten
minutes, with the a/c on. Except when it's below Freezing outside unless the garage is
heated. Silly me !
Should I remove the belt off season?
Definitely not, for doing so would not let you be able to exercise the a/c once a
week. Besides the belt uses nearly zero h-p when the a/c is idling.
What size belt does my a/c take?
A factory 911 from '71 through '83 will use a Dayco 17430 or a 17435 if you don't
have the strength to put the short one on. Using the shorter one will give you more room
to the right of the Compressor. Non-factory a/c's take a variety of Special belts, but
Dianna at (714) 634-9184 will know just which belt you need and have it in stock. All
these belts are going to a little hard to install, mainly because there isn't much room
for adjustment, so the belt must be tight at first or the Compressor can't move enough to
make it tight. To install a Factory belt, take all three bolts out, back the adjustment
nut all the way left, slip the new belt over the lower pulley and lift the Compressor as
far as possible towards the center, place the belt in the Compressor groove and let the
Compressor down and back into place. Start the three bolts again finger tight, then
tighten the adjustment nut until the belt is very tight, tighten three bolts and you're
done. Easy, eh !! On any a/c the belt must be very, very tight or it's gonna be noisy. For
those out there with an add-on a/c, screw in two 3/8 nc x 1" capscrews into the
Compressor in the holes closest to the head, now remove the two capscrews going into the
Compressor through the bracket from the bottom. Now swing the pump around so the belt is
loose. Replace the belt, then slip a long pry bar between those two capscrews you
installed and pry the pump back with one hand and start the two bolts with the other.
Will any York Comprssor work on any Porsche?
The answer is certainly a definite NO. There are 6 different Yorks used on various
Porsches and these really should not be interchanged. For instance most add-on units were
smart enough to use a 6 cu. in. York. DPD used a 6 in. Mini-York. VPC used a full
size 6 in. York and the Factory from 1971 through '83 used a Monster 10 cu. in. York. A
lot of factory a/c in domestic car will also use 10 in comp. but the problem that we see
is when someone takes their Porsche to a shop and the replace a 6 in. with a 10 in. and
then the clutch and/or the belt won't hold. Make sure that you get the same size
compressor that you had in the first place. Of course a 6 in. pump will work just fine on
a Factory system.
What about servicing the engine with a/c?
I realize that having that Compressor sitting there in the way can be a pain, but
on most models, just three 8 mm bolts are all that hold the lump in your way. Make
yourself a 18" square Pad of heavy plastic covered with an old blanket. Place this on
the fender, remove the three belt adjusting bolts, and swing the Compressor out onto the
Can I mix and match belts?
There are two different belt angles used on the Porsche a/c's and it is not wise
to mix them. If you have a 37 degree crank pulley, don't use a 60 degree Clutch pulley.
Take a good look or hold a belt into the groove, if the walls of the belt don't contact
the sides of the pulley, it won't work because all belts drive from the wall.
How much freon does my a/c hold?
All non-factory a/c's in 911's will be satisfied with 28 oz. of R12. The factory
a/c with a front Condenser and a double row rear Condenser will hold 39-42 oz. With only a
rear Condenser it should take 34oz. The Important thing hear is not to put in any more
freon that it takes to clear the Sight Glass on the Receiver/Drier. This MUST be checked
with the deck lid CLOSED and the engine running at 2000 RPM for a minute minimum. Putting
in more Freon than is necessary will do no good and only serve to make higher head
pressure, more heat and damage your parts.
Any Special treatment for the Porsche a/c?
Nothing, nada none EXCEPT Keep the engine lid CLOSED
when using the A/C !!
Why does my engine almost stall when the a/c kicks on?
Because one of two reasons or both of them, You have too much Freon in your a/c or
because you have a factory a/c with the Truck Compressorressor on it. This 10 cu.in.
monster was used only on trucks or large cars when Porsche chose it to replace their 5
incher. If you want a smooth engaging, smooth running, compact, lightweight Compressor
then the only choice is a Seiko- Seiki True Rotary Vane Compressor. When this Compressor
engages on the highway, you won't be able to detect it! A lot of a/c mechanics claim, even
swear that the Sanden is a rotary, and while they do indeed make one, you'll probably
NEVER see one. If it says 507 or 709 or 508 or 510 or 505 it is a swash plate with 5 or 7
pistons and 5-7-8-or 10 cu. in. displacement. York also made a Rotary for a short while
but no longer does. Nippondenso is also experimenting with Rotary as is Panasonic.
How do I read the Sight Glass on my Factory A/C?
Whereas most sight glasses are on the top of the Receiver/Drier, Porsche put
theirs on the side. What you are looking at is actually the level of the Freon in the
Drier. The little white ball in there is to let you know that the level is higher than the
glass so the ball will float and be at the top of the window. As soon as the ball floats
to the top of the glass, STOP adding Freon. Of course the car must be running at 2000 rpm,
HOOD SHUT, a/c on to read this.
My Factory A/C seems to use an awful lot of Freon?
Over the years I have found this to be true and I have yet to be able to say for
sure where it goes, but I firmly believe that the hose is to blame. I think that their
hose is just more porous than the rest. Another sure leak with the York Compressor on a
Factory a/c is the joint at the head of the Compressor Porsche insisted that York use Two
gaskets, an o-ring and the composition gasket it used before there was an o-ring. This is
WRONG with a capital W. If you have a '71 to '83 with a big York on it, take hold of the
hoses where they leave the Compressor, if they move up and down, then the gasket under the
plate securing the fitting to the head is broken and should be replaced. NOW use ONLY an
o-ring here, a special square cut o-ring, and oil it good. They should be tight as this is
NOT a movably fitting.
MY dash is Broken! What can I do?
Well if you have an early 911 or 912 and the plastic under dash panel is broken,
have NO FEAR !!! We have come up with an underdash bezel that
replaces four brands of a/c made for the Porsche.
What is that little TUBE coming from the thermostat?
That is a Copper tube filled with Freon that sticks into the Evaporator. coil and
senses the temperature. At a predetermined temp., it opens the circuit to the Clutch which
allows the temp to rise to another predetermined temp (usually +8 or 10 degrees) then it
closes the circuit again. This probe must have good contact with the fins of the coil or
it will allow the coil to freeze up and that is not good even if it sounds good. If the
coil freezes, the air must go around it and the air comes out warm instead of cold. So if
you notice that your a/c works at low speed (car speed) and then quits cooling after a
half hour or so, check this . Handle the probe very gently and polish the end with crocus
cloth before inserting into a new location in the coil if it was loose. The probe should
go in about 4" and at an angle to get between the coils.
What brand of A/C do I have in my 911?
A Factory a/c from '69 to '76 has three thin louvers on
either side of the ash tray and the temp switch. is on the left. The word Behr is on the
Evaporator. in the heater box.
A VPC has two slightly larger louvers on either side of
the ash tray and both of it's switches are mounted to the right of the ash tray. Their
logo is CCCCOOL
A DPD has the same two louver set up as VPC, the switches straddle the ash tray
but with the temp. switch. on the right. Logo is simple--DPD
Coolaire has a solid Plastic face that runs the WIDTH
of the dash and the ash-tray mounts below this. There are two large flex-tubes that jut
out from the firewall and carry the air to the dash. The controls are directly below the
steering column. Also has a large plastic bump under the hood.
Since '77 all the switches are mounted in the console so it's a little harder to
tell them apart but you will find a logo or brand tag somewhere on the unit.
There really is no clear cut Best one, each has it's own plus's and drawbacks and
each can be made to work as well as the rest. I'm sorry to say that the '77 was the worst
a/c Porsche ever put on the street. Only one small condenser and no vent under the dash
made this one sorry unit, but not to despair it can be updated.
What Vent are you Talking About?
Well, believe it or not, there is a small plastic deflecter covering a small vent
situated just above and forward of the console in the '78 through the present. Not many
owners have ever felt anything coming from this vent but it can be opened up and we have
an adapter that can greatly increase the amout of air that gets
into the cabin to cool you off.
How can I make my a/c colder?
If, after making sure the a/c is full, you don't think it is cold enough one
alternative you have is to add more condenser area to the system. A good way to measure
this is : Place the car in the shade, engine lid closed, place an accurate,
sensitive thermometer through the louver in the center of the car. If your 911 has a front
Condenser, check now to see if the fan is working, by holding your hand under the
Condenser while the a/c is on. You should feel a tiny whisper of air coming through the
Condenser, it doesn't get any better than this, but if no air is felt, get this fixed now.
Turn the a/c blower on to low, turn the thermostat to max, raise the RPM to 2000
and hold it for 5 minutes. The temperature of the air at the discharge should be between
36 and 42 if the a/c is working at it's peak. If the clutch begins to cycle (click on,
pause, then click back on) before it reaches this temp, it may be that you could adjust
the thermostat but I would leave this to a pro.. If your 911 is a late '76, a '77, or an
early '78 and has only one condenser on the deck lid you may not be able to attain those
temps and will surely need to add more Condenser to make yours work that well. For those
with non-factory air, your Compressor is a 6 cu.in. model, (at least it should be) so the
system doesn't need as much Condenser as Factory air but you could improve your a/c by
going with a little bigger Compressor and adding more Condenser. Another note, check to be
sure that the heater levers have completely closed off the heater ducts to the inside of
the car. If any heat is let into the interior it will fight the a/c and win!! Even the
best a/c can't overcome a weak heater!!!
A word about Fuses, circuit breakers and relays!!
For several years, the factory made the same mistake on every car with a/c. When
they wired the fuse board on the '76 to about '79, they wired the Evaporator. circuit
together with the Front Condenser. Fan circuit. So that all the elec. load was through ONE
fuse. Well since those ceramic fuses can hardly handle 20 amps. the load of 30 or 35 amps.
was way too much for them. The connectors turn blue, get loose and will actually melt.
Check your car and if the second fuse from the back of the fuse board is distorted see if
the red/white wire is connected with the red/yellow wire. If it is, separate them and
connect one of them to the next fuse which should be empty. A very good substitute for
these fuses or any fuse that seems to be overloaded (that is , gets hot ) is a circuit
breaker. A c.b. can be wired with a tighter connection, won't blow at the slightest
provocation, and will reset itself automatically.
Most all of these a/c's will have a Relay somewhere in the circuit mainly to
protect the delicate switches from the high loads of the motors. Most over looked is the
Factory relay located in the heater box next to the Evaporator.
What about TURBOS !!!!!!
When the Factory put air on all the turbos that came here they did some awful
stuff to them starting in '79 with the Mini-York that stood up tall and shook like Tina
Turner trying to get off that engine! Well, if there was ever an application that
out for a Rotary, this is it !! Then if you add a fan to the bottom of the Condenser. on
the lid, you can actually enjoy the car and the air !!!!
What about changing to r134A ?????
More about this a little later.............
Back to Previous Page