My in-law's 2003 996 HVAC controls don't seem to like small changes in temp setting. Note that they've had this issue for a while, but now my wife (for mother's day) asked me to help them fix the freakin thing.

So here's what we have:

1. Fans work in all steps
2. AC blows cold, heater blows hot
3. But it doesn't seem to like small changes in temp setting. I.e. - If I move the HVAC from 70 to 76F, I don't necessarily feel a difference on hotness or coldness of the blower.
4. If I move to 86F (it actually says HI for hi-temp), then it gets *really* hot. If I move to full cold, it gets really cold.
5. If I move to 85 or 83, it's still hot, but barely.

So I am thinking that it's some sort of cabin temperature sensor that may be dirty or "flap" that needs lubricating or something.

Can anyone make a suggestion?

 

You have to be sure the engine is fully up to temp.

If the car has the auto climate HVAC system if you increase the heat the heat may not come from the center or dash vents.

Based on my experience it comes from the vents at the base of the windshield vents then the under the dash vents.

IOWs, the air temp and amount of air from the dash vents, the vents at the base of the windshield, and the vents under the dash is not may not be the same.

The goal is to get the cabin to the temp selected but to avoid blowing a lot of air onto the passengers. Seems this type of AC behavior is not much appreciated by Europeans (I read somewhere) and frankly I'm with the Europeans on this.

While I like the car cabin at the selected temp I do not want to feel like I'm sitting behind a 747 with its engines at full song getting ready to take off.

'course even with the auto climate control system if one dials up the temp a lot then he will get a blast of hot air even from the dash vents.

Put the system in manual mode and select each vent area in turn: dash, at the base of the windshield, and the under dash vents, and verify with the other vents disabled by the appropriate vent select button and the vent area under test enabled you get close to the same amount of air from each vent. Could be a flap is bad or going bad or there's something blocking air flow.

 

...many thanks... All valid points. I tried the above and it appears all vents are blowing correctly with respect to whichever button I press to activate them. It just seems like the temperature that's blowing out of them isn't commensurate with the temp setting I put in place. It's almost, but not quite, like an on/off switch where the heat is off for any temp other than 86F (HI). I still get heat at from 70-85. It's just that when I go from 85 to 86, there is a HUGE (unbearable heat) difference in heat coming out of the vents.

They've been living with this for a long time. They tell me that they need to make 5F degree setting changes in order to "feel any difference". So in other words, if 70F seems a little too cold, they will need to set it to 75 or 76 to make the incremental change they want (vs. setting it at 72 or so). Note that in my Boxster S or C4S, the incremental change works.

? The only thing I can think of is there must be some sort of dirt in the interior temp sensor. Where is it located anyway?

 

Mine does same thing, until the car has been run for 1/2 hr or more. On my 15 minute commute, the auto setting is useless, it will fry me in the AM in the winter and freeze me in the summer. Wish someone made a simple manual setup to replace the digital controller. Also wish the darn thing would stay OFF when I set it to off and shutdown the car, but upon restart is resets itself to on. Dislike.

 

The interior temp sensor is behind the circular grill just beneath the passenger side vent on my 2002 996 Carrera. (according to the manual, as I have not accessed it).

 

Hmmm.....if one were to normally operate with the passenger vent closed, perhaps it might get confused WRT the actual temps? Its worth checking (scribbles note to self).....

 

Two days after I bought the car my friend asked me whats that (pointing to the roughly 2" circular grill). I said I think that's the tweeter.

Well, where is the one for the driver's side? Looking for it, I spotted the little 1" grill for the telephone mic and said that must be it.

Pays to read the manual. (I just hadn't had time yet)