doublecabmel

It's day 2 of driving my 993 in a row! Yay! It's been getting pretty warm in LA, so I decided to use the AC. I try to turn it on at least once a month to keep everything working. I hit both of the snow flakes and the air comes on strong. When I put my hand up to the 2 vents in the center; the driver's side one blows hard and the one to the right of that (pass side), is substantially weaker. Am I running low on freon? The a/c doesn't feel super ice cold. Of course I know 1997 Porsche AC isn't as good as some other cars. Thoughts?

mike cap

Double,

Two issues here.....

- Sounds like you have a problem with the servo valve in the RH side footwell. If it is partially opening that would account for the weak air flow. A common problem and easily checked and replaced. Make sure when you operate the A/C that all the dash vents are open and both sliders are all the way to the LH side. Of course the temp setting has to be fully counter-clockwise. The large snowflake button is all you need to push. This sets the A/C to MAX and RECIRC.

- The 993 A/C is adequate on most summer days. The easiest thing to do is stop at Home Depot and buy a simple probe style thermometer that the HVAC guys use. Put it in the center vent and drive the car. With the A/C on max you should see A/C cold temps close to 50 F. Anything below that is gravy. The best I ever see with a perfect system is 52 F. This applies to a typical summer day around 80 F. If it's 100 F in LA you won't see a 50 F outlet temperature. I have the factory chart for outlet temp versus ambient if you want. So look for 50 F or maybe a bit better and if you're getting that then the A/C system is giving you all it's got.

Hope this helps.

ToreB

HVAC fault finding and details here.
Cheers,
Tore

nile13

This is bloody normal. I'm not sure how many times this can or need to be repeated. It is normal to have high flow from driver's center side register and practically no flow from passenger's side. There is no problem other than with how the HVAC was designed.

Tore, I've asked you several times to simply go out to your car and check if it operates this way. I'd very much love to hear the answer.

OP, you don't need to hit both snowflakes at ones.

993/907

Yup, mine is the same way.
Just replaced some servos and the passenger side fan, and notice more AC air on driver's side than passenger.
Double, when you check the passenger side footwell servo make certain it closes completely....that duct is designed to always bring hot air into the cabin, and if partially open it will temper AC air.
Gordo

nile13

Why would anyone be checking servos before checking the simple things? Like the passenger's side register (not the center one, but the rightmost one). If that one has the same air flow as the leftmost register and driver's center register, your servos are absolutely fine.

Thank again, if a new owner wants to chase some non-existing problem to better bond with his 993... who am I to say no?

ToreB

nile13, I see your point, dont blow a fuse or something mate. All I did in this thread was to link my DIY page. I haven't been able to dig into this yet, you've asked me to do this twice. However, it's your theory, and you can't blame me for not having the time to verify it. By the way, I certainly don't disagree with you, and will try to grab my anemometer and help you as soon as possible.
Cheers,
Tore

nile13

Tore, no problem at all, I very highly respect your HVAC knowledge as well as your electrical skills.

I just want to make sure people don't chase an issue that's a non-issue. Hope you have a chance to verify the flow and put it in your excellent A/C writeups so the future owners can reference it. BTW, I don't even think you'll need any measuring device. The difference in flow from the two sides is so obvious that a hand next to each register on "3" or "4" setting or Max A/C setting will immediately verify this. I just think that most of us are surprised by this as we drive alone and never pay attention to the passenger's center register, nor any of the other car's I've ever driven have this "feature", so one simply doesn't think this could be right.

PS. Just as an FYI. I was looking at my air filter late Saturday. In talking off the filter box cover and then re-installing the clutch tube I managed to pull and disconnect a wire that is the positive signal for A/C clutch. So if you've done something around there - air box, top oil lines, power steering reservoir and suddenly your A/C is dead - verify that A/C compressor is actually turning when you press the snowflake buttons on. If not, follow the black wire down and to the right. Stupid is as stupid does, I guess. I've told myself not to do things in the dark a whole bunch of times... yet I continue to do so and it usually doesn't end all that well.

ToasterThief

Just bumping this thread in case anyone's still around to say "thank you." Earlier this year I replaced my driver's side servo. Today on a hot day I noticed that the passenger's side AC was noticeably weaker than the driver's side, but it sounds like that's normal with these cars.

os993

Really? Mine is doing this as well right now and I don't recall this being the case in the past. All vents work well, except passenger center vent. I would like to fix this.

Jbelt01

I can confirm the “passenger side” of my center vent has very weak airflow as well. It’s definitely an odd quirk, but so is everything else with this car. I have no idea if this is normal behavior or not.

Twilightblue28A

No, the condition described is not normal. The center has two (2) vents. Both should flow with equal velocity and equal temperatures. The driver side vent, under the instrument panel, and the passenger side vent, under the glove compartment, do not flow with the same velocity as the center vents.
Mike Cap gave everyone subscribed to this thread the best way to record temperatures.
​​​​​

os993

I have read many of these AC threads and I'm still not sure how to fix this. Is the right servo the culprit? The passenger side vent by the door blows perfectly. All of them do, except passenger central vent.

Twilightblue28A

This is the first time that I have read that the center vents are not discharging the same velocity. Most have written about headaches with the side vents or the vents discharging on your feet.
Mike Cap may still be on line and may provide an answer to your question. If not, Tore may respond to your question by tomorrow morning.
I'm interested in their responses.

Roman Mutlak

1995 C4 here. Similar situation. Left ( driver) and right vents blow at same velocity and temperature. Center vent, driver side has high velocity whilst right side is significantly lower. Both blower motors operate correctly at speed 4. Temperature is even across all 4 vents. Also wondering if this is the correct operation.