996 Heater Problem

[type-r]

I have a problem with the heating on my 2000MY 996 C2. The heating comes on but then gradually loses heat until it is only blowing mild air out. Is it likely that it has a faulty blower or heating matrix or something else?

[petop]

I remember someone going on about the valve going to the heater matrix can sometimes be vacuum operated. Do a Google search on it, may throw something up. If you loose the vacuum or its not as "vacuum'y" as it should be the valve can stick or fail. See if you can find an online parts diagram of the cooling/heating system?

[Rockster]

type-r said:

I have a problem with the heating on my 2000MY 996 C2. The heating comes on but then gradually loses heat until it is only blowing mild air out. Is it likely that it has a faulty blower or heating matrix or something else?

Both of my cars have auto climate control, but what I have noticed is that even though I do not have the A/C on as long as there is no Manuel [sic] on the fan speed LCD the system has some automatic climate control functionality.

The system will attempt to bring the cabin to the temp selected (my preference is 70F to 72F) and maintain this temp.

Now what I have noticed is that upon starting out cold the system will as the engine heats up blow warm air and the fan speed automatically selects a higher cabin fan speed.

However, as the cabin temp gets closer to and eventually reaches the desired temperature the fan speed drops and the temperature of the air coming from the center vents becomes rather cool.

What the system does as the cabin temp gets closer to and eventually reaches the desired temp is it directs more hot air to the vents under the windshield which works to keep the glass clear of fog and the cabin temp just right with little direct air blowing out of the center vents into the face of the driver and his passenger.

If you have an auto climate control system in your car, even if it is not in 'Auto' mode, even if the A/C is off (the snowflake symbol is dark) you may be experiencing the system doing its job. (I think it is a fine system and have become spoiled with its performance.)

If you do not have the auto climate control system and assuming it has no auto climate control ability whatsoever what may be happening is the flap that controls the amount of air routed through the heater core may be moving out of position and directing less incoming air through the heater core and as a result as you drive and this flap moves out of position and of course the air temp gets cooler.

I do not know if this flap is controlled/positioned and held in position by a vacuum motor -- I believe it is vacuum controlled in the auto climate systems -- or if the connection to the heat control setting is mechanical.

With the engine hot can you adjust the temp between max (hottest) and min (coldest) and does the air temp follow the setting you select? Does the fan speed stay constant? Does the amount of air and the temp of the air coming through the other vents (under the dash near the floor/tunnel and at the leading edge of the dash under the windshield) remain unaffected?

Sincerely,

Rockster.

[monthefish]

Rockster said:

but what I have noticed is that even though I do not have the A/C on as long as there is no Manuel [sic] on the fan speed LCD the system has some automatic climate control functionality.

This was my first thought.

OP - is it doing what you describe even in 'Manuel' mode?

[type-r]

Thanks for your replies, especially your very detailed response Rockster.

I do indeed have auto climate control, however I run it in 'manuel' mode on first start up. I raise the temp to say something like 22 degrees and then gradually increase it up to 25 degrees as I felt the air temp was fairly mild.

I will be taking it out for a long journey tomorrow morning so i will be in a better position to provide a more detailed analysis but as you said, it may actually just be functioning correctly based on inside cabin temp.

I'll be back in a couple of days and provide some feedback.

[Rockster]

monthefish said:

This was my first thought.

OP - is it doing what you describe even in 'Manuel' mode?

BTW, I made a mistake: it is spelled "Manuell".

Sincerely,

Rockster.

[monthefish]

Rockster said:

monthefish said:

This was my first thought.

OP - is it doing what you describe even in 'Manuel' mode?

BTW, I made a mistake: it is spelled "Manuell".

Sincerely,

Rockster.

Que?

[type-r]

Ok, so I took the car out for a good long journey this weekend and it indeed it seems to be doing what you suggest - seems to maintain the inside cabin temp (possibly blowing warm air out of the vents below the windscreen) and blowing mild air out of the front dashboard vents. The cabin temp was good for the whole journey. So looks like it is a non-issue

[monthefish]

Excellent. Thanks for the update.