993 A/C Evaporator /
Expansion valve replace DIY
Contributed by: TJ
1.0 Introduction
I would also like to thank
the Rennlisters that pointed me to helpful links that
gave me the confidence to tackle this job. I will attempt to document the
procedure I followed to do this job.
As you may / may not know the 993 A/C system is
practically like the 964 system of the early 90s. If you search
"evaporator" in the Rennlist 964 board,
someone posted a comprehensive instruction in removing the evaporator. I used this as a blue print in removing the
993 evaporator. I did find that there are
differences between the 2 cars that I will try to highlight.
I was leaking refrigerant
oil out the drain after fresh oil freon
recharge. The evaporator / air box drain is under the car between the 2 front
tires. The primary purpose of the drain is to allow rain or water entering the
grill aft the front hood or moisture that condensates (like water that forms on
the outside of a glass on a warm summer day) on the evaporator to drain under
the car. My A/C leak was so bad that oil would drip soon after Freon + oil recharge,
I could smell freon as well
with the blowers on high. An A/C charge would only last me a few days.
Overall, it is a job that takes time. I estimate I spent close to 15 hours from
start to finish including drier installation, evacuation, oil and charging of
the AC system. You can probably do this in 8-10 hours following the
instructions.
My impression from this DIY is that you need to be mechanically inclined and
have a few specialty tools that make the job easier (see below). I would say
that the toughest part of the job is working under the dash and dealing with
all the subcomponents of the airbox.
2.0 Evaporator /
expansion valve overview
The evaporator
is deep inside the air box between the dash and the firewall. It’s essentially
a radiator that gets really cold from expanding freon. Air is pulled through the evaporator, heat is removed from the air, and cold air
comes out your vents. The airbox assembly is inside
the airbox that sits directly below the air intake
just behind your hood.
I learned the hard way that it’s a good idea to replace the expansion valve at
the same time the evaporator is replaced. The
expansion valve is a $50 part that (in my case) can go bad and lead to cooling
problems as well. The expansion valve creates the pressure differential of the freon and hence cooling of the evaporator. It also regulates the flow of freon, with a temperature probe,
to prevent the evaporator from forming ice and reducing the cooling effect of
the AC system. Common symptom of an expansion valve that needs adjustment or
replacement is if the AC works when you first start driving then later stops
working.
Go ahead and order a replacement drier too - it contains a desiccant that must
be protected from humidity. The drier is located behind the driver side front
wheel behind the wheel well cover.
It is also recommended that every time you crack open an AC line, replace the
o-ring. Make sure the o-rings are designed specifically for AC systems and that
they are oiled and clean using the compressor oil (PAG)
To do this job, you will need to remove the gas tank, loosen fuel pump, remove
components in the dash, remove and disassemble the air box and finally remove
driver (US) left side wheel well. Plenty of opportunities to forget to connect
things etc. so take plenty of pictures as you go. I referred to my camera pics many times during assembly. Also, I found it helpful
to store bolts, screws etc in baggies to keep things organized. I labeled the
bags "fuse box", "glove box" "top airbox"
etc. Without doing this, I would have been lost.
Before you begin this job, it’s
a good idea to remove your stereo from your dash first. This way you can drive
to the stereo installation place, instead of depending on lady luck to hook you
up with a knowledgeable radio installer.
It also is helpful to drive
the car to leave little fuel in the tank. This will cut down your siphoning
time.
3.0 Tools for the
job
Below is a picture of the
tools that I used for the job. You will need to jack up the front of the car to
access the fuel pump.
I want to highlight a few of the tools:
1) Magnetic pickup tool - used plenty of times when retrieving screws - I don’t
know how I could have done the job without it. Magnetic tray is especially
handy when working under the dash to prevent screws from falling under front
seats or off the fender when you’re under the hood.
2) Mirror - great for under dash visibility.
3) Fender guards! I used 2 - one for the side to rest tools and fuse box and
another on the front bumper to protect paint finish as you climb in and out of
the hood.
4) Catch pan for fuel that must be drained.
5) Stubby wrench and universals for tight access, metric sockets and wrenches.
6) Metric Allen hex wrenches.
7) T-10, 15 torx wrenches.
8) Torque wrenches and breaker bar to open up the AC lines near the compressor.
9) Screw driver magnetizer to help hold screws during reassembly.
ps - There is a picture of PAG46 oil which is
supposed to be compatible with ND8 oil (Porsche spec). A fellow rennlister found ND8 oil at a MB dealer. On the back of the
ND8 bottle, it mentioned PAG46. I believe this oil is the lowest viscosity PAG
available. I found PAG46 at Pep Boys and steered clear of non-specific PAG oil.
Also, there is a quart of DURA flush
used to clean the system prior to recharging my AC lines. I bought the flush at
4.0 Removing fuel tank
Remove the carpet liner from
the trunk..
Now disconnect the battery.
The first thing that needs to come out is the fuel tank. To do this, fuel must
be removed. I found that by removing the fuel level sending unit, I could
siphon fuel out of the tank directly into another vehicle. Unplug the unit and
use a strap wrench to remove the sending unit.
Try to siphon as much fuel
out as possible; any remaining fuel will end up in your catch pan under the
car. I ended up with 2 quarts of gas when I drained the tank after siphoning.
After siphoning, put back the sending unit to keep the fumes down. Leave the
wires to the sending unit unplugged.
In the trunk near the external gas cap, you will find 2 hoses leading to the
fuel tank. Remove the 2 hose clamps on the lines. Remove the ones closest to
the fender.
Don’t worry about removing the mini-tank on top of the gas tank. I dont know exactly what this is - maybe an auxiliary tank
for fumes? DO NOT remove the hose that is running between the tanks. The entire
gas tank will come out as a unit!
Loosen the metal strap that secures the gas tank. It’s the metal band and
sheath that runs in front of the tank and bolts on the driver’s side of the
car. I could not completely remove the strap (it will come out later) but you
can bend it out of the way. Now you can remove the plastic sheath that is
between the strap and the tank.
Back under the car; remove the under-car access cover between the front wheels.
Toward the back of this cover, there is a smaller plate that must come off as
well. Above this plate is the fuel pump.
5.0 Fuel pump removal
The fuel pump is held in
place by 3 bolts. Disconnect the 3 bolts and let the pump hang. This gives you
more room to disconnect the fuel lines.
I found that the best way to disconnect the tank is to disconnect the fuel line
near the pump as well as the metal line. You will need a 17 and 19 mm wrench
for the steel line and 8 mm socket for the hose clamp near the pump. I
initially tried to disconnect the hoses near the tank. DO NOT try this. As I
was prying the hose lines, I was putting stress on the tank - I did not want to
break this!
Wear glasses and have the drain pan ready. Make sure your trouble light is well
out of the way. Fuel will come out of the line. We dont
want BBQed P-car owner do we?
I also want to mention that in this picture you can see the airbox
drain (black rectangular outlet to the right of fuel pump). If, after a
recharge with oil, you see any leaks from this area, thats a tip off that the evaporator
is dead or there is a leak from deep inside your airbox.
It might be helpful to
remove rubber/foam fuel line spacer that is wedged between the car and fuel
lines aft the pump access plate to articulate the fuel lines during removal. I
did this but probably not necessary.
6.0 Tank almost
out....
Go back to the top of the
vehicle and get ready to remove the tank!
Make sure you take the tethered hose clamp off and stuff somewhere out of the
way.
There is a rubber stopper thing that just pops out of its receptacle on the
upper tank. Hidden under is a 6 mm hose clamp. Remove it and take the tank out.
Notice in the pic that I have the fender cover on the
passenger fender in place? This is where the fuse box is going to sit. Also to
the right you can now see the firewall. Once the firewall is out, you will have
access to the airbox.
7.0 Firewall / fuse
block disassembly and dash work
OK - now that your tank is
out of the way. You are now looking at the firewall and fuse block.
There are a few screws that hold the firewall in place.
Screws #1, 2 and 3 are on the drivers side. #1 screw,
because of a spacer that is used looks like it does not have to come out. I
however could not get the firewall out without removing this one. It is tight
access here - my stubby would not fit. For the first time in my life of
wrenching, I actually had a use for my 90 degree Craftsman Phillips head
wrench. #2 and 3 are easy to get out.
Bolts #4 and 5 hold on what looks like a heat sink for the electronics of the
wiring harness. It’s basically a connector that plugs into an aluminum plate. I
think it’s a heat sink. When removing #4 and 5, you will need to hold the
backside nut and washer. An 8 mm box wrench is handy back there to prevent the
fastener from falling.
Also, now is a great time to remove the fuse block cover - it gives you more
access to the bolts.
7.1 Fuse block removal
The fuse block is integrated
into the firewall. In the picture below, you can now see the #4 bolt and 3
other screws that must come out.
Inside the fuse block, the black retaining nut actually has a phillips head screw inside it.
There is also an hex bolt that faces the shock tower
that comes out as well.
Ball ended hex wrench is handy, but not necessary since the shock tower is in
the way.
Now its
time to move the fuses and wiring harness out of the way. Definitely need fender cover and bungee to insure
that fuse block and wiring harness does not get in the way of the firewall
removal.
You cant
see it, but there is a screw in the firewall. it is
behind the wiring harness. Stubby Philips screwdriver is a requirement.
The last bolt is shown, it’s the last fastener before
the firewall comes out.
7.2 Airbox exposed
Ahh,
A thing of beauty - the airbox.
I labeled some of the components in the picture. You can see the airbox drains - the white tubing. You can also see the air
intake grill below the windshield.
Since you are under the hood, go ahead and remove both pollen filter covers and
the filters themselves. The covers are the two thumb screws and the filters are
keyed so that the tabs face upward. Make note when you take the filters out.
Go ahead and remove the air intake grill and retainer frame. If it has not been
done, now is the time to repaint the grill. Inside the grill, there are 2 bolts
that hold the airbox intake - go ahead and remove
them as well.
You can also see the 2 air conditioning lines (one is insulated) that are going
to the expansion valve.
Don’t remove those yet, we have stuff to do under the dash.
7.3 Under the
dash...
You will now need to remove
the climate control unit (CCU) in the dash. The best way to do this, if you don’t
have a tool, is to make one out of a heavy duty coat hanger. Do not attempt to
use a standard wire coat hanger - it did not work for me.
There are 2 electrical connections on the back of the CCU. I took a picture to
give you an idea how they disconnect. They swivel lock into place. Take your
time and look at the mechanism. Once you understand it, they are easy to
remove.
Also, the radio will need to come out. Mine was aftermarket, so I dont know what you need to do for stock radios. I got
really frustrated at this point because I could not get remove the radio. I
called a car installation place and luckily, I talked to a guy who told me the
secret - probably not a secret to anyone who installs head units for a living.
7.3.1 Glove box removal.
The Porsche manual says that
you must remove the glove box. I did. In retrospect, you may not have to. It
does give you more access, but I don’t think its a
requirement. You may wish to skip this step, and try airbox
removal without removing glove box.
I’m sorry, I don’t have any pictures of the glove box but I will leave you with
a few tidbits.
The face is held in place by 3 phillips
head screws at the bottom of the dash. There are 2 swivel brackets that must be
unhooked from the dash. When removing dash cover be
careful that under dash wiring is not preventing the hooks from coming out of
the dash. I found that the right side hook was much harder to remove. There is
a metal retainer that is held in place with phillips screw. I removed this for the glove box
cover to be removed. Finally, the GB liner must come out. I think there are ~6
screws that hold the liner.
7.3.2 three nuts under the dash.
If you look into the holes
where your CCU and radio used to be, you will see 3 nuts that hold the lower
portion of the airbox in place.
I tried to take a picture of these, but it was hard since the flash was
reflecting off the dash and not in the hole. 2 nuts are behind the CCU and the
3rd is behind the radio.
The first picture shows the CCU hole and the second picture shows the radio
hole. These three nuts need to be removed. (I incorrectly call them bolts in
the pictures)
In the last post, I outline
a vacuum relay that actuates the baffles below the airbox.
There is a vacuum line that is feeding this thing. Disconnect the line.
Also note that you must be careful not to damage this relay when taking out and
reinstalling airbox. It’s hanging out in the wind and
could be damaged.
We are just about ready to remove the airbox, so get
back to under the hood.
8.0 Evaporator replace DIY part 3: airbox
Ok - we are almost to the evaporator - Crack open the airbox,
swap evap, put everything together, and recharge. The
airbox is the most complicated portion of the DIY.
With that said, it looks intimidating, but actually not that bad. I strongly
recommend digital camera so you can refer to the pictures if you have a
question during reassembly.
8.1 Expansion valve
First thing to do is
disconnect the AC lines to the expansion valve. It’s the 10 mm bolt. Now you
can swing the 2 air conditioning lines out of the way. There is a retaining
screw that must be removed to move the lines. I use the hood to hold the lines.
The insulation protected the car finish.
You see the baggies on the lines? I attempted to close off the lines per good
HVAC practices; I soon abandoned this method for balloons that worked much
better.
Behind this bolt are two 3 mm hex bolts. Remove those, now the expansion valve
can come out. Pay particular attention to the O-rings. When reinstalling, you
need to use new o-rings. Matching up the replacement o-rings is critical to
prevent system leaks.
8.2 Disconnect
wiring harness and vacuum lines from box.
This step is easy; just
start disconnecting the harness, vacuum lines and drain from the airbox. Below are close up picture of the plugs that must
be disconnected. These stages seems like a free for
all, but take your time and refer to these pictures or your own for reassembly.
I will not pretend to identify each component of the assembly, but I’m sure
they all have a name....
I apologize that the pics are out of sequence (I can hear it now - why is the
expansion valve back on the airbox?) dont pay attention to this, my disassembly was not as smooth
as yours is going to go by following this DIY....
8.3 Air box air
ducts
There are 2 air ducts that
feed the airbox on the left and right sides. They
come up directly under the pollen filters. Each duct has 3 plastic snap
connectors that must be depressed before the airbox
can be removed.
If you are not careful, the plastic ducts can crack when removing the airbox. I believe the 993 is different than the 964 in this
area. I believe that you can reuse the existing ducts if you are careful. The
common thought is that the ducts must be replaced on the 964.
If you press down on the duct, it compresses a little in the trunk floor to
give you more clearance. DO NOT press down on center bar on the inside of the
duct - that piece can and will break - ask me how I know!
8.4 More airbox disassembly
Now that the airbox is out, we need to take off some more topside
components labeled in the picture.
Take your small flat blade and remove all the small retaining clips around the
entire airbox. There must be 20 of them.
You will find 4-5 torx head screws that need to come
out as well.
I forgot to mention that on the top of the airbox
there are 2 temp sensors (?) toward the back of the airbox
that must be removed with a T-10 torx screwdriver.
Finally, there are 2 hidden screws in each of the fans. These must be removed
to separate the 2 halves. If you turn the fan, you will find that Porsche keyed
the fan hub to line up with the screw heads for removal.
You might want to consider
checking the brushes on the blower motors to see if they are almost worn out.
If they are consider replacing the motors.
8.5 Cracking open
the airbox.
The 2 halves of the airbox come apart easily. If they don’t, you must of missed a screw or clip.
Wow, look at the nasty evaporator. With all the gunk, it couldn’t cool anything!
Because of the leak, oil from the AC system must have gone everywhere
externally and my evaporator was like a K&N
air filter!
9.0 Home stretch!
Reassembly of the new evaporator and airbox is
reverse of the procedure outlined above.
Once the airbox is reinstalled and harness connected,
follow instructions below before you connect the expansion valve and AC lines.
You may want to add 1/4 oz of UV dye to the new evaporator.
It will make leak detection down the road much easier. I injected it directly
to the new evaporator. You can see the dye in the evaporator in the pic below.
Go ahead and attach 2 balloons to the evaporator
inlets just to prevent junk from going into the evaporator.
Did you notice that we have
not installed a new drier yet? That is because we need to flush the AC system
and get rid of the old oil and "leak stop" stuff that I jammed in
there hoping for a real easy fix.
The drier is a dessicant that must be kept under
vacuum and pristine. We install that as part of the last step. I will get to
that in a moment.
You can either buy/borrow a vacuum pump or get a venturi
type vacuum for compressed air. I fortunately had a vacuum pump at work that I
could borrow. The venturi vacuums are very noisy. I
have seen many vacuum pumps on EBAY for $100-200.
Using my AC manifold gauges, I hooked into the high and low side of the air
compressor. The red line is high pressure and the low side is the blue line. I
attached the vacuum to the yellow line and started the pump.
Back to the AC lines that connected to the top of the air box - I used a
generic plastic cap to close off one line at a time, but found that a balloon
works well. I inserted each line separately into the Dura
141 AC flush can. I used a quart for the entire system (1/2 qt for each line).
This stuff is expensive at $28 / quart (
9.1 Compressor
disassembly.
Back at the compressor, it
was memory lane, the red leak stop, oil, UV dye from the past was being
extracted from the system.
Now that your system has been flushed, we need to get rid of the old oil in the
compressor. Disconnect the high and low pressure lines into the compressor.
These need to be removed for access inside the compressor. These 2 bolts take a
lot of torque to remove. Porsche put a thread locker on these. I used a
1/2" breaker bar and you can see where my socket deformed the bolt heads
slightly.
Once the two lines are disconnected, removed the long bolts
that hold the compressor in place and disconnect the AC belt. Now you
should be able to put the compressor on its side and start removing the 4 hex
bolts.
I found a contradiction in
the PSM as far as oil capacity. One place says 100cc of oil, another says
140cc. I chose to err on the high side and added about 4-5 oz of PAG46 oil
(half a bottle - see picture of part one if you want to see the bottle)
directly to the compressor with the access cover off. If any refrigerant is inadvertently
bled off, you will loose a little oil anyway.
Reassembly of compressor is reverse of disassembly. From alldatadiy:
* Tightening torque of compressor mounting bolts (M 8 x 125 bolts): 28 Nm
* Tightening torque of refrigerant pipe (M 8 x 32 bolts): 23 Nm Replace all
mounting bolts during each reassembly (micro-sealed bolts). Replace O-rings and
coat lightly with refrigerant oil.
* Tightening torque of service valve (4 bolts): 25 Nm
I have to admit I reused the mounting bolts of the refrigerant pipes and I
forgot to change the o-rings!! The PSM says change both - probably good advice
considering how the bolt heads were slightly deformed during disassembly. With
the UV dye and easy access to top of compressor, I can monitor this location
for leaks very easy so I won’t loose any sleep over it.
I almost forgot to mention
that there is a little black wire that runs from the compressor to the right
side fender (under a plastic cover). Reconnect this line or your compressor
will not come on.
9.2 Back to
expansion valve and install new drier.
This step was the most
frustrating part of the DIY.
We are now going to reassemble the expansion valve to the evaporator. See in the close up picture of the expansion
valve, I fitted new, oiled o-rings to the evaporator.
This was the only way I found to insure proper seating of the o-rings.
I found that the 3 mm hex bolts must be very tightly bolted to the evaporator. I don’t have a 3 mm torque wrench, but I can
say that after many blown o-rings on my pressure tests, cranking down on my hex
wrench was necessary to getting a good seal. My 3 mm allens were deflecting a considerable amount.
Alternate tightening of these 2 allens
for even compressive force. And seating of the o-rings.
The same is true for the 10 mm hex bolts where the A/C lines bolt back into the
expansion valve. I had to put 140 in-lbs of force into the bolt so that it
could hold the o-rings in place during my pressure test!
Make sure you only use new, oiled o-rings in all places.
Back to the manifold gauges - I used the vacuum pump to pull a vacuum on the
system. The picture does not show it, but my pump was capable of -1 bar vacuum
- good, not the absolue best, but good enough. I let
the pump run for 30 minutes to insure all moisture removed and then closed the
manifold gauges and shut off the pump. Your system must now be capable of
holding vacuum with no measurable pressure lost for 3-4 hours. (Some online
articles suggest 30 minutes, but I think that is too short.)
As far as belt tension, get one of those v-belt tension gauges. The PSM says 30
scale increments. See picture of the v-belt tool below.
9.3 Finally the drier
If you did not successfully
pass the vacuum test, recheck tightness of retaining bolts and insure you have
the right size o-rings not cuts whatever. It makes no sense to proceed until
you correct this problem.
Let’s remove the drivers’ side wheel and wheel well splash guard behind the
tire. The drier is pretty simple, 2 lines that connect to the top and a strap
holding it to the car.
Sorry I did not take any picture, but its pretty
self-explanatory. Again new oiled o-rings and remount on strap. The refrigerant
lines should be retorqued to 10 Nm.
Repeat vacuum test to insure seal at drier is sound.
9.4 Pressure test
Usually the vacuum test is
all that is needed to insure your system is ready for freon. I found this not to be the case with the Porsche.
With the car in its current state, I used the manifold gauges to inject
approximately 30 psi of R134 refrigerant into the AC
system.
I found that if you did not sufficiently torque the expansion valve bolts (2 allens and 1 10mm bolt), you could
blow off the o-ring at 30 psi.
I, unfortunately, found this out after passing vacuum test, reinstalling
everything, filling tank with gas and having an o-ring blow.
Because I told you this hint - you will not go through the misery I faced of
another disassembly!
If your o-rings hold, you are ready to reassemble firewall and gas tank.
10.0 Recharge AC
system
The Porsche compressor is a
little different than your average car. Optimum low side pressure is around
10-20 psi. Most generic non-Porsche AC manuals say
that low side pressure should be 40-50 psi. If you
put this much freon into the
system, you compressor will short cycle or never actuate.
The system capacity is about 3 1/2 to 4 cans of R134 (840g)
Fill the tank with 1-2 gal of gas and start the car.
Turn on the AC system on max and begin to charge the AC system with freon.
ALWAYS INJECT FREON ON THE LOW SIDE ONLY. ACCIDENTLY INJECTING THE FREON ON THE
HIGH SIDE MAY LEAD TO THE CAN EXPLODING!!!!
Below are Porsche specs for AC system (high side compressor pressure, low side
compressor pressure, and vent temperature @ 2k RPMs
all as a function of ambient air temp).
Drive around a few days
before installing the carpet under the hood. This will help you monitor gas
leaks whatever.
