[tamathumper]

Does our AC compressor switch off at <acronym title='wide open throttle'>WOT</acronym>? I was just reading about another Porsche that has that feature, and I don't see anything about it in the Owner's Manual or the workshop manual.

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[Ryan]

Out of curiosity, how modern was this other Porsche you read about? I don't think our cars A/C cuts out at <acronym title='wide open throttle'>WOT</acronym>, but I could be wrong. My wife tells me I'm wrong all the time and I don't even know it.

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[MB968]

I may have missed it, but I didn't see a vacuum operated switch in the wiring diagram. So, it doesn't look like we have one.



It would be quite simple to add. There is a single line that runs to the compressor that supplies 12v to the clutch. I'm not sure where you'd find that type of switch that is normally closed with vacuum and open with atmosphere. But there must be something like that used on other cars. If we could find the switch, it's just a matter of putting it in the line to the compressor. Might be a nice feature to have.

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[flash]

it wouldn't take a vacuum operated switch, since we have a TPS.



it would be easy to test though. merely insert a light bulb on the power wire to the compressor, drive, and see what happens.

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[tamathumper]

@Ryan, I thought it was the new Cayman, but I can't find the article again - it was one of those random Internet romps.



I came out of a toll booth yesterday and stepped on it pretty hard and the AC went all warm and humid for a few seconds - I supposed it could have belt slippage, but I re-verified that the supercharger belt is still at 50 pounds as measured across the top span, which I'm assuming is tight enough?

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[986boxster1998]

Tama,



I've got a vacuum leak that I believe makes a large difference in the ac at <acronym title='wide open throttle'>WOT</acronym>; I just found it last night and its the tube running from the bottom of the intake manifold up to the vacuum canister thats just off the oil fill tube. Maybe thats your issue as well. I tracked down some pictures and part numbers last night and can post them when I get home.



My friend that sold me the car told me his other 968 did the same thing and that all 968s do this, but I've owned other 968s aswell and dont recall the AC fading or getting hot with acceleration (plus its a little hard for me to believe that my daily driver a 2000 Ford Explorer has a better AC design then our 968s).

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[tamathumper]

I have been looking for vacuum leaks as part of another issue, but nothing obvious has shown up - I do intend to look again, though. I needed to get a better gauge setup, which I have now. By vacuum canister do you mean the blue check valve? Please post an update if your vacuum leak fixes your issue.

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[986boxster1998]

Here is a picture of the fitting on another car were I found my leak (the rubber had brooken away at the elbow):

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[flash]

that's the air/oil separator.

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[John]

There's a small blue plastic check valve on the vac line back along the fire wall on the passinger side which serves to isolate the climate control system from the normal variations in vac due to engine load and speed. It leads to a small vac "storage" canister under the cowl cover next to the battery, and to the climate sys with it's vac operated air doors. If there's a vac leak somewhere that side of the check valve, the canister has less buffering effect, one or more of these doors don't stay fully open/closed, and you hear or sense a change in the air flow, which is most notable when the AC is on. The first place to look is the elbow on the vac line where it connects to the heater control valve. These crack, on the under side where you can't see them, due to the heat bath from the exhaust manifold.

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[flash]

very well put

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[psuphoto]

If I even suspect that I'll need that <acronym title='wide open throttle'>WOT</acronym> might come into play, I'll preemptively press the internal <acronym title='wide open throttle'>WOT</acronym> switch (aka AC switch) off. A habit I started in 1982 with my first Honda Accord. Poor man's SC or should I say CS (Club sport). LOL <img src="/forum/images/smilies/968/EmoticonCar.gif" class="smilie" alt="" />

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[986boxster1998]

[quote name='flash' timestamp='1372789709' post='145169']

that's the air/oil separator.

[/quote]

Thanks I did some quick reading about the function of the air/oil separator which said pretty much like the name suggests it take oil/vapors out of the air. What seemed interesting it that if not hooked up it can cause the gas/air mixture to be too combustible, much like using lower octane fuel. If it interpreted all of this correctly is probably even more important that those of us with forced induction have this separator in working order.

[quote name='John' timestamp='1372793318' post='145175']

There's a small blue plastic check valve on the vac line back along the fire wall on the passinger side which serves to isolate the climate control system from the normal variations in vac due to engine load and speed. It leads to a small vac "storage" canister under the cowl cover next to the battery, and to the climate sys with it's vac operated air doors. If there's a vac leak somewhere that side of the check valve, the canister has less buffering effect, one or more of these doors don't stay fully open/closed, and you hear or sense a change in the air flow, which is most notable when the AC is on. The first place to look is the elbow on the vac line where it connects to the heater control valve. These crack, on the under side where you can't see them, due to the heat bath from the exhaust manifold.

[/quote]

Thanks I'll be going over everything again; I put a new plastic <acronym title='heater control valve'>HCV</acronym> on my "to order" list after reading numerous threads about failures.

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[tamathumper]

Checked vacuum at the <acronym title='heater control valve'>HCV</acronym>, it was only 12 inches, so I tried three different methods of finding a vacuum leak. First I did the "stethoscope method" and found a slight hiss on the little ported connector at the top of the throttle body. Second I tried the "soapy liquid" method and found only the same tiny leak. Thirdly, I tried the dreaded "starter fluid" method, but that didn't make a difference at all.



I sealed up the one connector as best I could, and the vacuum still dropped from 5 to 3 psi in about 2 minutes, then stayed at 3 for a very long time... so I'll get another piece of hose for that one connector and try again tomorrow.

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[flash]

well, at least we know why you are having a running condition problem. you have a leak somewhere, which is what i thought all along. all ports should be full vacuum (16"-18"), except the one at the top of the throttle body, which is ported.



you may have to disconnect all vacuum lines, cap and plug everything off, leaving only the line to the fuel pressure regulator connected, and then add them back one at a time until you find the problem.

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[Cloud9...68]

Or do a smoke test

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[tamathumper]

I ordered the full vacuum line kit from Lindsey Racing for good measure.

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[MB968]

When I pulled my engine, I was surprised to find that all the steel nipples for vacuum lines that came out of the intake manifold were loose. In fact two of the three could be easily pulled out of the intake. So, you may want to check these, don't know if this is common or not, but suspect it may not be uncommon since all of mine were loose.



Solution was to swage the end of each steel tube (after getting it out of the intake manifold) for an interference fit. Drove it back into the intake with some 3M bearing gap eliminator on it to make for a secure sealed connection.

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[gbarrier]

Way back when I had an old 4 cylinder diesel Mercedes. While I loved the old dog and drove it over 500K it would not get out of it's own way. <acronym title='wide open throttle'>WOT</acronym> was normal start off procedure. I put a big old micro switch at the throttle and when it hit wide open the a/c dropped out. Very simple and worked well.

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[DaveN]

Referencing Ryan's post #2. I though there had been many posts here over the years with people querying the loss of A/C at <acronym title='wide open throttle'>WOT</acronym> and that it was accepted that the A/C kicks out on purpose with that condition. If it is indeed just slippage then the micro switch idea is well worth the install. As an SC owner I never hit <acronym title='wide open throttle'>WOT</acronym> <img src="/forum/images/smilies/968/rolleyes.gif" class="smilie" alt="" />

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