[banditsc]

[quote name='Cloud9...68' post='40381' date='Aug 25 2007, 12:30 AM']OK, what I thought was the correct fitting is actually the high pressure side. Summer has finally arrived here in Austin, so it's very uncomfortable in my garage, so to save me a little time hunting the thing down, where exactly is the low pressure fitting where I need to fill the R134? I didn't see it on thetop side, and sasilverbullet mentioned putting the car on a lift, so I imagine it's underneath. Thanks.[/quote]



It should be on the bottom side of the compressor. You really need to remove the plastic tray from underneath to get at it.

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[Cloud9...68]

[quote name='banditsc' post='40384' date='Aug 25 2007, 05:32 AM']It should be on the bottom side of the compressor. You really need to remove the plastic tray from underneath to get at it.[/quote]

Thanks; I was kind of afraid of that. Normally not a big deal, but it's suddenly very hot and MUGGY here in Austin, so this is not going to be fun. I'm glad I asked, because my sense of dread would have had me searching ANYWHERE but in the area hidden by the plastic tray.

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[sasilverbullet]

That's where EVERYTHING on our cars are, behind the shield... <img src="/forum/images/smilies/968/smile.gif" class="smilie" alt="" />

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[Cloud9...68]

I'll see when I get under there, but for those who have done this before, were you able to just remove enough of the screws to move the shield out of the way, or did you have to remove the whole shield? Thanks.

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[banditsc]

[quote name='Cloud9...68' post='40403' date='Aug 25 2007, 05:50 PM']I'll see when I get under there, but for those who have done this before, were you able to just remove enough of the screws to move the shield out of the way, or did you have to remove the whole shield? Thanks.[/quote]



You need to remove the back piece of the plastic tray. Just three bolts in the front and four or six or so in the back and two phillips on the sides. That is of course depends on how many bolts that have been put back on you car after the numerous time it's been removed over it's life.

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[Cloud9...68]

Ah, so the fitting is behind the MIDDLE shield. Luckily, my car doesn't have a middle shield, so this job was SO easy. My freon was maybe 8-10 ounces low (very rough estimate, based on how long it took to get from the "low" or "green" zone to the upper end of the "Good" or "blue" zone on the gauge that came with the can of R134). It now blows nice and cold. Thanks for all the tips! So nice to find an easy and cheap fix to a problem.



As far as the middle shield, I've heard that it helps with the air flow under the car, in addition to providing protection to belts and various other sensitive components from road debris. Anybody ever add a middle shield to a car that didn't have one when they bought it? If so, could you quantify any difference in the reading on the temperature gauge? My car always runs nice and cool, never getting above 9:00 (maybe 9:30) on the gauge, so I'm wondering how much room for improvement I have. Even if it doesn't aid cooling, this is something I'm planning to get due to its other benefits, I'm just trying to figure out where to prioritize it. Maybe I should start another thread on the topic of shields...

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[sasilverbullet]

nah, don't start another thread... <img src="/forum/images/smilies/968/smile.gif" class="smilie" alt="" />



Before we start down the "shields" thread - let's make sure we're all on the same page...



From front to rear:

1. Under the front bumper is a black plastic shield - we'll call that the "front piece"

2. Now there is a second shield that is right under the front of the engine area, it's the biggest one.

3. The third shield is pretty much right under the clutch housing area.



From what I've read over 5+ years of reading rennlist and other forums - having them all in place will reduce the amount of drag underneath the car, thereby helping to create a little negative pressure area and thereby increasing the amount of downforce on the front of the car.



I had a 87 944 Turbo, (very similar) and when first purchased it didn't have the front piece under the bumper - car was VERY light on the front after 110mph until I replaced it, then the car handled fine over 110mph.



I can't personally speak for what exactly happens with a 968 - there, let the fun begin! <img src="/forum/images/smilies/968/smile.gif" class="smilie" alt="" />

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[banditsc]

A third one behind the large one? I don't think I have that one, I will have to go check the car, that one isn't ringing a bell. I do see it listed on the PET diagrams though. Or wasn't that one dropped on the post 93 cars?

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[Richard]

The 1992 model year 968s have three shields. I don't know when the third (rear most) shield was discontinued. The PET may show the difference.

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[Cloud9...68]

I definitely only have the front piece - no middle or rear. The fastest I've driven the car, at Motorsport Ranch, is barely 100 mph, and I haven't noticed any issues with lightness at the front end. But I plan to take it to Texas World Speedway one of these days, which is a much faster track. Am I likely to have any issues with under-car turbulence due to my lack of a middle shield? A front piece costs about $325 (mine's pretty banged up, and could stand to be replaced) - any idea what a middle piece costs? Thanks.

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[sasilverbullet]

Middle and rear pieces are metal and expensive new - get them from a junk yard - as far as the amount of difference, I don't think it will be that noticeable unless your pushing the car to it's limits.



Let me know when you're going to the track - I might be able to meet you there, I'd love to track mine also, nicely, smoothly - no wait, I'll "Drive it like I stole it!!!!"

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[banditsc]

My middle piece is plastic. You should be able to get it at a junkyard for around $100. I think I saw DCAuto selling them for $106. It's part # 94450416703

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[Cloud9...68]

[quote name='banditsc' post='40452' date='Aug 27 2007, 07:54 AM']My middle piece is plastic. You should be able to get it at a junkyard for around $100. I think I saw DCAuto selling them for $106. It's part # 94450416703[/quote]



Cool, that's not bad at all. Thanks.

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[flash]

middle is hard plastic - extremely effective in promoting cooling and downforce



third is metal - i believe it got cancelled somewhere in 93 mfg



also a very nice addition in cooling, but i haven't had the car over 130 since i installed it, so i can't confirm the downforce increase to any certainty, but the physics are very sound, and i'd swear the car feels more planted - however, i did a lot of other engine bay aerodynamics work at the same time, so i am not sure what is responsible for what

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[Cloud9...68]

[quote name='flash' post='40511' date='Aug 27 2007, 08:29 PM']middle is hard plastic - extremely effective in promoting cooling and downforce[/quote]



Do you have any way of quantifying the cooling effect, even something as crude as "temp gauge needle used to get to 9:30, but now never gets over 9:00." ? As I said before, my car never gets much above 9:00, particularly at high speed, where I imagine the shield would be most effective, so I wonder if I have any real room for improvement in the cooling department. I'm sure Porsche put these shields in for a good reason, and the protection of the belts from road debris is reason enough, but I'm just wondering if I would really notice any cooling benefit. Thanks.

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[sasilverbullet]

hmmmm, hard to explain - flash please correct me if I get this wrong, keep in mind there have been a lot of LONG threads over the years about the benefits/pitfalls of these pans...



My understanding is that there is a "negative pressure" differential at the rear of the pans, this aids in "sucking" the hot air from the engine compartment. Supposedly more so than if the pans weren't there.



I know you've read over the last months all the headache I've had with running hot and that my problem is over since going to a lower temp fan switch and lower temp thermostat and water wetter. Keep in mind I've had all the pans on throughout this whole ordeal.



Hope that helps <img src="/forum/images/smilies/968/smile.gif" class="smilie" alt="" />



Oh, and now my needle sits at the 8:00 (bottom white line) position even at 99 degrees in traffic!!!

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[Cloud9...68]

[quote name='sasilverbullet' post='40516' date='Aug 27 2007, 09:46 PM']hmmmm, hard to explain - flash please correct me if I get this wrong, keep in mind there have been a lot of LONG threads over the years about the benefits/pitfalls of these pans...



My understanding is that there is a "negative pressure" differential at the rear of the pans, this aids in "sucking" the hot air from the engine compartment. Supposedly more so than if the pans weren't there.



I know you've read over the last months all the headache I've had with running hot and that my problem is over since going to a lower temp fan switch and lower temp thermostat and water wetter. Keep in mind I've had all the pans on throughout this whole ordeal.



Hope that helps <img src="/forum/images/smilies/968/smile.gif" class="smilie" alt="" />



Oh, and now my needle sits at the 8:00 (bottom white line) position even at 99 degrees in traffic!!![/quote]



Wow, that's even cooler than mine runs. The thing I'm having touble grasping, though, is that the cooling effect of sucking hot air away from the engine should be more effective the higher the speed. But this is exactly when you need additional cooling the least. Kind of like a banker - he'll gladly lend you all the money you want, provided you can prove you don't need it.



Oh, and I also have a low temp fan switch, but, as far as I know, the standard thermostat, and no water wetter.

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[flash]

yes, the pan creates a higher negative pressure zone behind the radiator (is that a double negative?)



this causes more of the high pressure air in front of the car to be forced through the radiator and out the back - the faster you go, the more the effect



similarly, the pans create a low pressure zone under the car, as they do not allow the air to get lost in the engine bay - this is almost like the bernoulli principle, making air go faster in one place than another, thereby creating lift (or in this case, downforce)



when you need the cooling most is when you run the highest rpms - it really isn't speed relative so much as it is relative to the amount of heat generated by the increased number of burns in the same amount of time - work equals heat

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[andym968]

well after 2 weeks and offering my experience earlier in this thread, my AC stopped working today.Yesterday was fine, today just warm air....am lost, any ideas.Can it have anything to do with having my Navi system fitted earlier????

Want to save another trip to Porsche Center so any tips welcome..



thanks

andy

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[Cloud9...68]

Well, I thought mine had died suddenly as well, but it turns out the appearance of suddeness was more a function of the performance of the A/C relative to the ambient temperature. In the morning or after dark, it "seemed" to be perfect, but in the middle of a hot, sunny day, it "suddenly" stopped working. Mine isn't a daily driver, which added to the impression of "it worked perfectly, then all of a sudden started blowing warm air."



But in fact, as sasilverbullet suspected, it was just low on freon. For about $10, you can buy a simple gauge that will tell you if you need to add freon. Since I had become pretty convinced that I really was low, I went ahead and bought a $21 18 oz can of R134 with oil and sealant added. The can came with a built-in pressure gauge, of the same type I meantioned above that costs $10. The low pressure fitting is right below the fitting, and if your middle shield is missing like mine, it's very easily accessibe. I just followed the instructions on the bottle - with the AC running full blast, I put the fitting from the bottle on the low pressure fitting, and got an indicated 20 psi, which is below the recommended minimum of 25 psi. So I just pressed the nozzle until my reading was in the upper end of the "good" zone, which is 45 psi. It blows very cold air even in the middle of the day now. Of course, I don't know what caused my freon to leak out, but I'm hoping the sealant will at least slow the process. I'll check it again next summer.



I just wish I had weighed the bottle befre and after the fill-up; I can only estimate that I used about half the bottle, or 9 oz, but that's just a guess.



If your AC really did die that suddenly, maybe it's something else. Do you know anyone with a pressure gause, of a partially-used bottle of R134 like mine that comes with a gauge, so you could test the pressure of your system? This would at least rule this out before moving on to more expensive causes. Good luck.

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