I would 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 fellowrennlister 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 NAPA.
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 (Napa). Definitely wear gloves - this stuff is a very aggressive solvent. The vacuum pump with the help of gravity should help pull all the old crap back to the compressor.
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.