tj90

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 guages 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 under the hood - I used a generic plastic cap to close off one line at a time, 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). Please dont write back and tell me I got ripped-off! Definitely wear gloves - this stuff is a very aggresive solvent. The vacuum pump with the help of gravity should help pull all the old crap back to the compressor.

tj90

Back at the compressor, It was memory lane, the red leak stop crap, 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, disconnect the AC belt. Now you should be able to put the compressor on its side and start removing the 4 allen bolts.

I found a contridiction 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 pic of part one if you want to see the bottle) directly to the compressor with the access cover off. If any refrigerent is inadvertantly 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 almost forgot to mention that there is a little black wire that runs from the compressor to to the right side fender (under a plastic cover). Reconnect this line or your compressor will not come on.

As far as belt tension, get one of those v-belt tension guages. The PSM says 30 scale increments. See pic below for a pic of the v-belt tool.

I have to admit I reused the mounting bolts of the refrigerant pipe 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 wont loose any sleep over it.

tj90

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 pic of the expansion valve above, 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 allen bolts must be very tightly bolted to the evaporator. I dont have a 3 mm torque wrench, but I can say that after many blown o-rings on my pressure tests, cranking down on my allen 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.

The same is true for the 10 mm allen 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 mainfold guages. I used the vacuum pump to pull a vacuum on the system. The pic 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 guages 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.)

tj90

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.

Lets 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 pics, 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.

tj90

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 guages to inject approximately 30 psi of R134 refrigerant into the AC system.

I found that if you did not sufficently torque the expansion valve bolts (2 allens and 1 10mm bolt), you could blow off the o-ring at 30 psi.

I, unfortunatlely, 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.

tj90

The porsche compressor is a little different than your average car. Optimum low side perssure 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).

tj90

Drive around a few days before installing the carpet under the hood. This will help you monitor gas leaks whatever.

Thats it. Hope the DIY was helpful....

Martin S.

You are a DIY god!!!!

epj993

Great work, TJ!

How does the A/C work? Does it seem colder, work better?

chris walrod

Ahhh, the great mystery (to me anyways) of A/C work. Great job!! I really enjoyed this write-up, and thank you!!

jnx

Nice write up. Thanks.

tj90

Eric - the AC is within spec shown above - anywhere between 5 and 8 C. My leaky evaporator was so bad that I would charge the system and could smell the freon pouring into the cabin. A fresh recharge would only last a few days...

Contrary to previous 911 model years (3.2 etc), the 993 has a good OEM AC system. Definitely no complaints - of course, Im not in AZ desert driving around either. I wonder if the PO ditched the car because he was not a DIYer and he knew there was yet another big $$ expedeture coming to repair the AC...

tj90

Actually, HVAC is a closely held secret. It took months scouring the internet to find bits and pieces of information on how to do it. Most people dont know anything about it - for example, most guys at the LAPS dont know what AC flush even is, that there are different grades of PAG oil.

Not much of a conspiracy theorist, but I think the lack of information is on purpose. I was repairing my homes HVAC (new starting capacitor for the outside compressor) and I found ALL local supply houses that would not sell to me. Dont the local guys care that they are loosng business to internet supply houses? Maybe its a licensing or union thing. Thank God for the internet.

--tj90, president and CEO of rennlist mechanical LLC, est. 2006

slider

TJ - my car is in the shop as we speak for this very fix. Even tho I'll not diy this one, your posts were very helpful in understanding the process and speaking the same language with the mechanic. I hate paying for this stuff and I know its a lost oppty to learn more about my car but frankly, I'm happy to have someone else do this fix...

that being said, can't wait to do the suspenstion install...

tj90

Joe did you fix the airbag light? Your helpful posts have caused me to put a note on top of the battery post saying to not jump or charge battery in excess of 2 amps while battery is connected to car.