ventilation air being heated

I am dismayed that I cannot get fresh air ventilation that is not heated. Is this a commonplace for the 996? With the HVAC controls set to Manuell, temp Lo, center and floor vent selected (fan speed doesn't seem to have any effect), I am getting air through the vents that is distinctly hotter than the ambient temperature. I have tried running the fan on a higher speed, thinking that air idle in the ducting, e.g. while parked, could have become heated, but the condition persists indefinitely. The heating is not so high as using the heater can make it, but hot enough to make fresh air an undesireable setting on an otherwise beautiful day. I've been trying to figure out how the air is being heated. Fresh air enters the system at the trailing edge of the front hood at the base of the windshield on the right side. There is a compartment enclosing the filter element that is sealed off from the trunk proper by a weather seal. This compartment is open to the battery, the strut mounts, and such. The only thing I can come up with is that air heated by flowing over the right front brake is exiting the wheel well and being carried upward to mix with the flow across the hood. Anyone else have any experience with this problem?

It's not in the owner's manual. Try this: 1. Set temp to LO 2. Set fan speed to any manual setting 3. Turn OFF the compressor (A/C) I think you're missing #3.

It has to be as simple as ervtx says. I routinely use vents only when at the track, no AC. The air temp that comes out is the same as the ambient temp.

I really don't think that is the problem: this a factory A/C-delete car. (Anyway, in an A/C 996, if the A/C were switched on with the temp set to "Lo," wouldn't the air would be quite cold, not heated?)

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The servomotor that controls the fresh/REHEAT mix is out of calibration. It should be able to close off ALL airflow through the reheat path and apparently it is not. Some cars have the ability to completely close off the hot water flow through the heat exchanger eliminating even the reheat airflow leakage and the radiant heating effects. If nothing else you might want to have a technician add one to your car, assuming it doesn't have one already

Juan, I'll check those areas out. ervtx, an A/C delete car does not have that button. There are three rotary ***** (hot/cool; fan speed; vent selection) and a recirculate button. Since this is an unusual option, I tried to relate the problem in terms more familiar to most 996 owners. So, here it is: **** all the way to cool, fan at any speed, dash & floor vents selected, recirculate off. I can tell the difference between a hot day and heated air. (Give me a little credit.) If the answer was obvious, I'd have found it by now. That's why I ask if anyone else has had the same problem. Only sources of heat at front of car are radiators and brakes, but none are particularly near the air intake. Makes me think Juan is on to something.

This morning I spoke with my mechanic about the heated ventilation air. He acknowledged that the duct gate servos can be calibrated, but suggested that the symptoms would persist anyway. For one thing, the gates are not pressure seals, so some heated air may still be drawn past the closed gate. Secondly, and most significantly, the area of the gate will be heated by the heater core and may permit the fresh air to be warmed in passing. The radiator-like core sits upright at the back of the ventilation stack. In fact, from the battery compartment you can see the two hot water lines that serve it (supply and return). They are 1/2 inch hoses to 90 deg. elbows into the firewall a few inches apart behind the battery. On the 9x6 series cars, hot water runs to the core all the time. Whenever the engine is at normal operating temperatures, the core is going to also be heated, sitting up there behind the dash. The solution recommended by my mechanic is putting a valve in-line on the hot water supply so that water can be prevented from running to the core. It would be a mechanical valve that I would open seasonally as the weather cooled enough to warrant having cabin heat available. I think I can locate the valve within reach behind the battery. (I have a smaller, racing battery, so there should be room.)

Dogs do love trucks! Hank

Hey, there, Hank. How ya been? I took the GT3 to Barber in April and had a great time: after doing Little Talladega in March I felt much more at ease with the handling characteristics, so I could work on finer points at Barber. Are you going to Road Atlanta for the June PCA weekend? Have you realized yet that you must get a GT3, too? One of my PCA instructors suggested a little trail braking to induce some oversteer to counteract the usual initial understeer entering a turn. Does that sound right to you?

The early eighties MB 300D had an electrical, 12 volt, water flow control valve, you might want to use one of those. But were I you I would still get the air mix servomotor calibrated, and I would check and make sure something is obstructing/blocking its travel in hot flow closure mode.

M-P, I�m glad to hear that you are enjoying the car. I bought a �99 996 and am really enjoying it. I would like to buy a GT3 but it�s just not in the cards at the moment. I am probably going to the June PCA DE at RA but not 100% sure yet. Regarding trail braking, that�s not why I use that technique at some turns nor is it how I think about it, but I can see that it could be used to that effect, especially later in a session. For me, trail braking is a way to carry a little more speed into a corner without sacrificing exit speed. It is more something I can �get away with� rather than something I need to do. I would rather have my car set up to handle the turns like I want rather than having to compensate using trail braking. Having said all of that, you have to set the car up for something, either early, mid or late session conditions. I always set my car up for new tires and the early session segment. The thought being to get away from the �competition� and let them burn up their tires trying to catch me. It is not a bad strategy, however, to set the car up for mid or late session conditions and try to pressure and ultimately pass the competition when they have less grippy tires and a setup or style that doesn�t lend itself to sliding. Everyone has a style that they are comfortable with and if you can consistently trail brake a corner to maximize that segment�s speed then it is a valid use of the technique. For me, I like to be as consistent in each corner as possible, once I believe that I have maximized my speed through it. Hank

That puts the technique nicely into perspective. Thanks.

I know this is an old thread, but I just recently purchased a 01 996 w/ A/C and am having some weird problems and was hoping someone could help me. This was the closest thread I could find. When I turn on the "auto" feature and say set it to 72 degress a few problems happens.(A/C automatically turns on at this point) First: there is a discrepancy between the temp of air coming out of the front vents vs. the temp of air coming out of the windshield vent. The temp on the windshield vent is SIGNIFICANTLY hotter. To the point that I have to lower the temp to say 66 degrees and at that point when the w/s vent is at a manageable temp, the front vents are too cold. Any ideas? Second, if i switch it to manuell and put it to the front vent, there will be hot air at say 66 degrees and then if I put it to 65 degrees, it sends out super cold air. I have let it go for a while b/c originally I thought it needed time to adjust, but I don't think that's the problem. The w/s vent has the same problem, but i have to set it at a lower setting for it to get a good temp. It's weird b/c I don't think 66-67 degrees on manuell w/ the fan speed at 1 bar (lowest setting) on just the front vents should be the ONLY solution for me to have comfortable temp. The temp in WA this time of year is moderate and today was approx. 60 degrees when this happened. Thanks for reading this. Paul

cabin temperature sensor is open

wwest, I appreciate the quick response... newb question... where can I find that sensor? The manual doesn't list it (matter of fact, the manual doesn't list much of anything... are there other manuals you recommend buying?) Thanks.

The cabin temperature sensor is behind the round mesh "window" on the right side of the dash near the passenger door.