urban_alchemist

So, the weather's turned (well, apparently it turned a while ago, but I've been in Asia for the best part of a month), and I'm rolling into the first summer with the 993TT...

Today was the first time I had need to switch on the AC... small snow-flake, and between 1 and 2 on the fan. Whenever I accelerated, the AC would cut out, coming back on when I eased off the throttle... Temperature was unaffected, but it was just a little annoying.

Is this common with 993s?

kennyboy

Are you sure it was only when you accelerated?

The AC does come on and off noisily and often in the 993.

BS911

Vacuum leak. When you accellerate and load the engine, vacuum manifold pressure drops, and your recirculated air flap can no longer hold open against its spring. When it closes, there is no air input and it chokes off. You can search here on the "wheezing" a/c for more threads.

Or there is an AC diagnostic article I wrote over on p-car.com here --> http://p-car.com/diy/acdiag.html

993_Pilot

+1 on the Vacuum leak, I had the same experience.

urban_alchemist

Thanks guys... as the DIY is equivalent to reading Chinese (actually, I think my Chinese is better), how long should a vacuum leak take to fix?

Cheers...

BS911

Chinese? Ok, thanks.

Could be 10 minutes, could be hours. Depends on where the leak is. You have vacuum pressure but not enough. When you hit A/C, the system goes into recirc mode. The electric servo closes outside air and relays vacuum pressure to a flap behind your stereo/CCU to open up the inside air inlet. When you accellerate and the engine is under load, your vacuum pressure is reduced and the vacuum line can not fully hold the air flap open against its closing spring, so it pulls shut. When that happens, air flow stops as the fans can no longer get any air to blow. Once you let off the throttle, vacuum pressure returns and the inside air is opened again and you get the cooling sensation of an arctic breeze blowing through your hair.

I would start under the dash - looking for the vacuum line. A very small diameter, hard plastic hose connected to a rubber 90 degree elbow. If you have had any stereo work or anything under the dash, it could very well be loose in there. Make sure that connection is snug. If that is good, go to the solenoid under the front hood. (More info in the Chinese document.) Make sure that both connections on that are good. This is where you go from 10 minutes to a couple hours... if those are good, that line source comes from the engine area. There are a bunch of places to lose vacuum pressure. It could be a cracked vacuum canister, loose elbow, anything. I'm not sure what the best way to track vacuum leaks there is, maybe someone else could have further info on that part.

chet

I seem to remember reading about a connection piece back in the engine compartment that can sort of lose it's structural integrity and collapse (sort of like sucking too hard on a straw). It's supposed to be back behind some stuff, and may not be easy to see. If your vacuum problem isn't up front, that piece might be the culprit.