A/C stalls engine

[Sean Hamilton]

Every time I pull up whilst the A/c is running, the engine rev's drop..... way down and stall - engine stops.
It'll do it also whilst stationary in neutral - rev the engine A/c on and on the way down the revs drop to zero - stalled.
Turn the A/c off - starts immediately, no problem (albeit a bit rough)
Leave the A/c off - no stalling at all.
PITA in traffic!

I'm a bit annoyed as I've just spent big bucks getting the 200k service done including A/c re-gas. They haven't returned my calls and it's now way past thier knock-off time.
So, naturally thought I'd ask you blokes.

Thanks, for any advice.

[dtw]

Usually a sign of a seized AC compressor. Been down that road many times.

[Sean Hamilton]

Originally posted by dtw
Usually a sign of a seized AC compressor

Hmm, okay I'll check that out. How do I tell?

It's only two and a bit years old but it is an after market compressor that the PO installed.
Wonder if I may have buggered it up by not regularly operating the A/c during the winter? (gas always leaks out the rubber hose walls so it was useless running the A/c. Still......)

Thanks Dave, for the quick reply.

[Sean Hamilton]

Okay, I pulled the pulley belt off the compressor - pulley wheel spins and spins freely.
So the stalling is only occurring whilst the compressor clutch is engaged - A/c is on.

I recall on some older vehicles there used to be a solenoid that would trigger upon A/c clutch engagement and up the idle a wee bit to cope with the extra engine load. Is there something like that on a Porsche engine fitted with A/c? That maybe is disconnected?

Thanks.

[SeaDweller]

I had the same problem.....When I'd let off the gas (with the A/C on), the engine RPM's would drop below 500, and the engine would stall. For some reason, the deceleration valve didn't catch the fall in RPM's. Believe it or not, this was related to a mild engine surging, that I corrected with a mixture and timing adjustment. Once I had the mixture and timing set, the problem disappeared.

[Hladun]

If the compressor is seized, the pulley can still turn freely when the A/C is off. Try turning the inner part of the pulley assembly. If should be harder to turn, but you should be able to turn it. Alternatively, apply 12 volts to the compressor clutch and then turn the pulley. It should still turn quite freely.

[stormcrow]

Sounds like they may have overcharged your system. If the compressor was seized you would smell rubber burning. Take it back where the work was done and have the put their gauges on and check the pressures.

I don't know if your P-car has a selenoid on the throttle to compensate for the additonal load but if it does, then this could also be the problem.

Mine doesn't (78 Sc Targa) and I know when i overcharged the system, the idle went way down.

Steve

"A Porsche does more then just go fast in a straight line"

[Superman]

So lemme get this stright. Your A/C adds 70 lbs to your car, stalls your engine, and you're not sure what to do. Just kidding. Some folks really do need a working A/C system. I'm glad I don't.

[Sean Hamilton]

Originally posted by Superman
So lemme get this straight. Your A/C adds 70 lbs to your car, stalls your engine, and you're not sure what to do.........

Yeah yeah, I know. Even when it is working it's bloody useless! Porsche obviously had the same attitude Super! But I suspect this to be more a symptom of the actual cause itself - engine tune?

Steve:
I'll get 'em to recheck for overcharging ....... and on the invoice too!!

Hladun:
Thanks, I've now done what you said - "turning the inner part of the pulley assembly should be harder to turn, but should be able to turn it" so the compressor is working fine.

Michael:
Yes, I'm leaning toward the mixture setting.
Interestingly the car is now bunny hopping (surging) whilst slowly coasting in 1st and 2nd (A/c is off) Horrible! Like I'm an L plater? Embarrassing! Never used to do that. I suspect they've stuffed up with the idle/mix setting!

Thanks all - Porsche Centre Melb are now collecting the car to have another crack at it and re-tune it.
I'm not impressed! The $$$$ we pay these guys you'd reckon they would at least road test it before handing back the car.
I'll let you know.

[SeaDweller]

When I say Melbourne, I was going to give you a recommendation on an awesome engine tuner, but you're in the wrong (or right, depending on how you look at it ) Melbourne!!

[Hladun]

Last summer I rebuilt the A/C system on my 78 SC. I had the original evaporator. I had new hoses made up (biggest cost item), bought a deck-lid condenser and compressor bracket from Parts Heaven and got a used Sankyo compressor of a wrecked SAAB for $20. I use only the single deck-lid condenser. The most important thing I did was get a pancake fan from JC Whitney to blow more air through the condenser (search on my name for other posts on this topic). I then charged the system with R134a. I get 8C vent temperatures when it’s 35C outside. Here is the secret…..you must get more airflow through the deck-lid condenser or the system just can’t work. The problem with the Porsche A/C systems on older cars is that they can’t reject heat.

[Sean Hamilton]

Michael, you were spot on - the mixture/idle setting. Too lean.
I'm amazed at the difference! That mix/idle settings can have such an effect.
I think that they now may have gone a little too far the other way? Now, when I take my foot off the accelerator the RPM drop and then hang, up there at around 2k, then slowly drop back to 950 rpm. Maybe it was always set too lean?
Still, it certainly doesn't stall anymore and seems to be more driveable - now with the revs hanging up there between gear changes. Just gotta get used to it.
Thanks all.

Originally posted by Hladun
........had new hoses made up ......The most important thing I did was get a pancake fan from JC Whitney to blow more air through the condenser.............

Yeah, that's what I'd like to do - change the hoses, These old OEM hoses are a sieve - regassing every 6 months. I like your suggestion of a pancake fan for the decklid condenser. Was there sufficient room to fit it under there without mods?
Thanks Hladun, I'll check it out and your past threads.

[SeaDweller]

Glad you got it fixed Sean.........That "hang up" in the RPM's is likely the deceleration valve. It's designed to do just that.