ScubaJKD

Need some help guys. When I accelerate with the AC on it will quit blowing then when I let off the gas it will start blowing again. Any ideas? Thanks in advance for any thoughts.

Terry Adams

Like most modern cars, it's meant to do this. To get more power to the wheels when you need it.

BS911

Vacuum leak most likely. Search over for the diy or hit p-car.com for the same to diagnose.

ToreB

I'm also having this issue.
My serviceman has changed my A/C evaporator due to refrigerant leaks. That's working OK now.
But, when accelerating I get a "phophhhh" + wheezing sound an the air stops flowing.

I have done some fault finding based on p-car.com and Brians DIY. (thanks!) Fresh air servo is OK, and there seem to be a vacuum leak somewhere.
Max A/C or Recirc buttons turned on operate the vacuum solenoid under the windshield, and the Inside Air Source flap operate. I can see this when I remove the CCU. But, the flap is not always fully opened, and fluctuates/moves when I hit the accellerator. (flap closes when revving up)
That, combined with maximum fan setting is creating the "phophhhh" sound.
Elbow tube is connected to flap operator OK, and all vacuum connections around the solenoid are OK.
I can feel the vacuum in the black solenoid feed hose but cannot determine if it's OK or too weak.
I suspect there is some leak in the front somewhere since all components in there has been removed due to the A/C evaporator change. But I cannot rule out a leak in the engine area.
Question 1: Where is the black vacuum feed routed from the solenoid and back to the engine? Where in engine bay is the other end?
Question 2: I have no vacuum gauges, is it possible to measure or test the vacuum in the feed hose? Should my finger stick hard to the hose end ?

This could help me isolating and finding the leak.
Regards,
Tore Bergvill
Oslo

Marlon

I have the same problem.

jackb911

So do I...I'm pretty sure a vacuum hose has become disconnected, but I have no idea where to look.

ToreB

I'm still working on this.
It seems that only A/C Max setting produce my problem. I have watched the Inside Air Source flap when experimenting with different settings.

Max Fan, Recirc on, upper and lower slide setting to minimum and A/C normal on: Inside Air Source flap smacks open and stays there. Normal air flow.
If I then hit A/C Max button the flaps become "saggy" and throttle dependant. Air flow depend on flap opening.
I also have ruled out vacuum solenoid valve fault, the same happens if I bypass the valve. (connect the black feed directly to the white line routed to the flap)

I'll say, strange behaviour... What does Max A/C setting do besides the manual ones I've described above? Maybe some leaky vacuum line is connected via a valve in the engine room?
Any tips will be highly appreciated.
Regards,
Tore

Marlon

There's a small section in the Streather book to test the 993 system vacum for the '95 cars and 96 & later cars. Will look at it this evening.

farmerjohn

Isn't there a resister on the fan circuit that, when failing, causes erratic fan speeds?

ToreB

We're not discussing the outside condenser fan placed in the left front wing, but the inside air flow. Fan speeds are all OK in my car.
By the way, I have changed both my resistors/ballasts on both the A/C and oil cooler fan.
Regards,
Tore

Marlon

It's not electrical - it is a vacum issue. A vacum leak in our a/c ducting controls is causing the problem. I can say that when I experienced the problem in my black 95' 993, I was found a disconnected vacum line in the area in front of the dashboard in the trunk. I simply reconnected the line and wa-la, no more problem. In looking at my red 95' 993 however, those lines are connected, but I have the same problem. Have not really looked at it hard yet.

ToreB

Still digging in this in the garage. I really am confused now.
I've tested more combinations of the CCU controls and my problem also relates to the temperature setting.
Low temp setting, A/C low on = Flap opens, but sags throttle dependant
Same result with no A/C and Recirc on
High temp setting, no A/C, Recirc on: flap opens and stays there.

This makes me wonder, should A/C on, low or high actuate the recirc solenoid and flap at all?

I've also checked all visible vacuum hoses and couplings in the engine compartment. They're all OK.
This is really getting on my nerves now...
Regards,
Tore

Marlon

Bugging me too - since I can't find any 'leaks', I'm thinking it might be related to the CCU itself???

ToreB

I have found out that my CCU fan is failing. (the small fan at the back of the CCU) Maybe that's fooling the CCU to do this to me. We'll see, I have already ordered a new fan. It'll be some days for delivery.
I can't believe this is my problem though, but I will ease down on the job until I at least rule out that one.
Regards,
Tore

PDriver

Remember: if any of the vacuum actuators is perforated, the vaccum system is cutting out if the fault vacuum actuator is activated.
If the vacuum system is not working, your car loses performance because the resonance/varioram flap is out of order...

Check this points:
for the 272hp engine
- for vacuum reservoir look at your engine bay under the left air intake pipe (black plastik piece)
- check all your vacuum actuators: heater flap, resonance flap, aircon flap for leaks (try to apply a vaccum to check if the actuator is perforated)

for the 285hp engine
- for the vaccum reservoir look at your engine bay at left of the firewall (plastic bubbles
- check all your vacuum actuators: heater flap, resonance flap/varioram flap, aircon flap for leaks (try to apply a vaccum to check if the actuator is perforated)

On my car one actuator was perforated and some porsche mechanic disconnected the vaccum line from the reservoir when he changed the generator.

PDriver