Porsche Enthusiasts Club Forum

I am in the process of changing the heating over to warm, I do this by just removing the glove-box and removing the rod to let warm air in the cabin rather than cold. I have been doing this with the car as the seasons change from hot to cold for the last few years.

I read that the system defaults to hot if the rod dislodges, mine does seem fine and I do fit the rod myself for the Summer months and remove it for Winter as I have just done, as its only a 30 minute job?

What I would like to know is what is causing this to not work as it should? I see some mention the vacuum tank in the engine bay, the vac pipes to it are fine so how do you check it is working? Also could it be the control unit in the dash or most likely the Vac tank?

Also does anyone know how does this vacuum actually works the controls, what does the vacuum activate? I was looking at what I could see today, with the control unit and glove-box removed but I can't fathom how the vacuum interacts with the heater controls? Electric connections, to vacuum to mechanical arms seems complicated?

It’s probably the vac valve not working
Down by the oil filter

I can’t grasp that you take the glove box out a few times a year to move the rod and never wondered about fixing it

There is a complete description of how it all works with test procedures on Clarke’s garage site

I had wondered about fixing it but I have so many other more important jobs on the go it was easy to overlook looking into this one for the 1 hours work a year it takes.

Unfortunately CG's site seems to be down at the moment, unsure if its been a long term issue or just recently?

I'll have a look at that valve, I didn't realise it was also part of this system?

here is a link to clarks page that seems to be back up now

http://www.clarks-garage.com/shop-manual/ts-10.htm

Perfect thanks, I'll see if I can get my head around it before I put it all back together.

I've been having a look around this today, I think all the vacuum pipes seem to be connected correctly and i can't see anything broken anywhere. I will look into changing the Vac tank soon and report back.

I think the valve that was mentioned near the oil filter just lets the flow of coolant through, correct me if I'm wrong here?

Yes it does, switched but vacuum

All the things are interconnected by electrical or vacuum

If the vac tank was broken your vac system would be not working correctly which would affect your fuel pressure regulator

They are all connected

I changed my Vac tank out today but the heater still blows hot with the rod near the glove-box disconnected and only cold with it connected.

I've been looking through the CG guide and wondered what would be next thing to change? Should the heater solenoid on the drivers side (UK) of the heater system be the next thing to change? I'll also have a good look at the vac lines behind the dash while I'm there.

Is it also possible the main control unit could be at fault, they aren't cheap, even used so I don't want to replace unless necessary?

I have a spare control unit you could try if you are willing to post it back

Thanks, that's very kind of you, I am going to be testing the solenoids under the drivers side dash today by putting power through them to see if they are working. I have them off already and still connected in the vacuum system under the dash but I ran out of time to test. I'll give you a shout back if that is unsuccessful.

If not successful, you should also check all 3 temperature sensors are at least plugged in. If one of the 3 sensors is not plugged(sometimes cars have been worked on & left disconnected for whatever reason) the HVAC will go to default, which is Heat.

I've not had chance to test the solenoids as yet the car's outside and its been very chilly but I'm also not sure I have any temp sensors as I don't have AC anyway? I know there is definitely not one behind my little round grille on the dash where one is supposed to be located?

There is one in the air box of the heater another one in the air intake by the wiper motor, and some cars have one in the bottom of the NS wing mirror

OK when I'm togged up at some point this week or the weekend (double figure temps apparently) I will also check those locations, thanks both.

The oval dash has 3 temp sensors, whether you have AC or not. These all have to be plugged & read accurately as previously mentioned.

The one you mentioned(behind small round grill) should be there, but will be further back behind glove box. A tubing is connected from the small round grill to the sensor. You should just about see the sensor & mounting by lying down in passenger foot well facing upwards to windscreen. Start with this.

Second at blower air intake under bonnet driver's side(near wiper motor as Waylander stated).

Third, behind center vents in dash.