kkim

First off, the a/c works just fine other than this one problem.

When I first start the car and have the big snowflake pressed, so the a/c is running full blast, when I start off in first gear and accelerate, the blower fan speed gets weaker. As I let up on the gas to shift to second, the fan blows full blast again. Seems to happen only in first gear when, I suspect, vacuum draw is high. Does this indicate I might have a vacuum leak somewhere and how does this tie in with the a/c blower? Fan weakness seems directly proportional to engine speed. (engine speeds up, fan slows down) After the car warms up, the problem doesn't occur in first gear.

Car runs fine otherwise.

Any ideas on what to check?

KASH '95 993

kkim,

That sounds really strange...my car has been doing just the opposite (as the rev's increase the fan speed goes up). I assume my problem is a faulty (on its way out) alternator.

User 4221

Kelly,
Fan is electric and independent of engine vacuum. Fan speed is proportional to system voltage.

Based on your explanation, I would suspect a voltage regulator. You may only notice the behavior in 1st gear as it sweeps the RPM range fastest and makes the issue present itself more noticably.

I would do a simple voltage check at the cigarette lighter. Measure the voltage with the car in neutral while revving the engine similar to the rate of change of 1st gear.

If the voltage moves above 14.4V or below 10.8V then you need to investigate further.

Let us know what you find.

jkuniverse

Kelly, I know they have a different symptom but since they both relate to the "big snowflake" button, pulling out and cleaning the CCU might do the trick as it did on mine. Good luck to you.

https://rennlist.com/forums/993-forum/211430-a-c-blower-motor.html

kkim

Scott-I'll check out the VR.

Jason-Some of those posts may be in the right direction as it does seem to be vaccum related.

Mahalo for the tips, guys... it at least gives me somewhere to start in trying to figure out what's going on.

mlincoln

The fan is electric, of course, but the mechanical "gates" that direct the air to various combinations of vents, depending on your settings, are driven by vacuum. I had exactly your problem, until the dealer reconnected a vacuum line during an oil change.

Mike

kkim

Thanks, Mike. I must have knocked something loose when I was fumbling around when working on my car recently. Will look around this weekend and see what I can find. Relieved to hear that it is most likely not something major and others have had similar problems.

Lorenfb

"The fan is electric, of course, but the mechanical "gates" that direct the air to various combinations of vents, depending on your settings, are driven by vacuum." - mlincoln -

There's NO engine/pump vacuum used in the 964/993 CCUs. All the actuators are driven by
small electrical motors with feedback elements to determine their positions.

As mentioned previously, monitor the battery/alternator voltage.

kkim

As a follow up... I found a loose vacuum line when I was doing my SAI passage clean out. When I had changed the SAI valve a few, months ago, I inadvertently knocked a line off when I disconnected the large rubber hose from the top of the SAI valve. The DIY that I was following did warn to double check the line , but it is really hard to see/find unless you know what you are looking for. Just a word of warning.

Anyway, a/c functions like it's supposed to now. Thanks for the help.

Aussie Alan 993

Sorry guys, I just read this and amazingly knew the answer...

For anyone who wants to know more about the A/C system and airflow, search under "air by-pass flaps" you are sure to find some useful info.

Cheers
Alan

KTM

Did you notice any other symptoms from this disconnected or loose vacuum line, like rough idle?

Any pictures of where that vacuum line is?

thanks

kkim

Alan,

Yes, I had read a lot of old posts and that is what kind of pointed me in the direction of a vacuum leak somewhere as suggested in my initial post. Just thought I would follow up so the next Rennlister who has similar problems will be helped out from my solution.

kkim

One other symptom.. I was getting a P0410 CEL code due to the SAI problem I was having at the time and perhaps this code was being triggered by the disconnected hose. I also was getting a P1411 code which was telling me I had a plugged port, which is what led me to go in there the second time to discover the loose vacuum line.

Sorry, no pictures, but it is located above the SAI valve. No need to worry about his vacuum line being loose unless you went in there to play w/ that SAI valve hose. To gain access to it, you must remove your airbox.

Aussie Alan 993

That is the great thing about this board, people genuinely want to help others and many problems have already been successfully resolved and the solutions been written about.

I have had more answers from this site and others like it than from the "Experts"

Bull

Glad you found your problem! When I had a problem with the air flaps not functioning properly on my '97, it was vacuum leak related, AND the Varioram was not functionig properly either. Actually, my search for the V-ram problem led to the fix for the AC flaps as a bonus (the AC was a secondary issue to me at the time).