993 Heater permantly stuck on a very long road trip
Discussion
My 993's heater has been stuck on full heat for a very long drive down from the Scottish Western Isles to London. I tried the air-con, but all that did was make the fan throw out the very hot air even faster!. Has anyone else experienced this problem?, is it a case of something simply coming loose or am I in for an expensive fix?.
Is the heat coming from both the passenger and the drivers side? If only coming from one side it is probably the motor on the hot air control valve. You can find this by removing the panel in the outside corner of the footwell. I had this and it was a relatively easy DIY to fix.
If it is a problem with both sides it could be the controller which is a bit more expensive.
Have fun
Steve
If it is a problem with both sides it could be the controller which is a bit more expensive.
Have fun
Steve
sfl993t4 said:
Is the heat coming from both the passenger and the drivers side? If only coming from one side it is probably the motor on the hot air control valve. You can find this by removing the panel in the outside corner of the footwell. I had this and it was a relatively easy DIY to fix.
If it is a problem with both sides it could be the controller which is a bit more expensive.
Have fun
Steve
Steve, (thanks for replying)If it is a problem with both sides it could be the controller which is a bit more expensive.
Have fun
Steve
It seems to be more on the drivers side. I experienced a very hot foot, but my passenger didn't. Though we both experienced the heat from the corner air vents by the respective doors. the middle vents were less so. If I turn the fan control up, it puts out hot air faster.
If it is the simpler problem, the motor, how will i know if it is not working, should it make an operational noise, or vibrate? If it is the worse of two scenarios; the controller, can I fix this myself. I have the 993 full repair manual and Pet Catalogue. one other thought, it rained constantly while in the highlands, one of my dials misted slightly, could a simple blown fuse be the cause?
I don't mind having a go with a screwdriver and manual; it's not the daily driver, so I have time on my side.
From memory, (mine was the passenger side, but I'm sure that its much the same).
There are two pipes (one on each side)that run from the rear of the car to the front carrying hot air forward. The amount of hot air on each side is controlled by a valve (so theoretically I guess that the 993 could have a split aircon system with different temps for driver and passenger if the controller was up to it).
If you take look in the footwell, there is a panel in the front outside corner which covers the valve and pipe carrying the hot air. I think that the panel is only held on by a couple of screws.
Once you've got the panel off, you can see the gate valve (big black plastic thing) and the large pipe either side. If you undo one (or both) of the hose clamps you can see the valve itself (it may simply be stuck). If you then adjust the aircon you should be able to see the valve itself move.
If not it could well be the motor that has siezed or died (I took the motor on mine apart to try to fix but ended up buying a new one).
Have fun.
Steve
There are two pipes (one on each side)that run from the rear of the car to the front carrying hot air forward. The amount of hot air on each side is controlled by a valve (so theoretically I guess that the 993 could have a split aircon system with different temps for driver and passenger if the controller was up to it).
If you take look in the footwell, there is a panel in the front outside corner which covers the valve and pipe carrying the hot air. I think that the panel is only held on by a couple of screws.
Once you've got the panel off, you can see the gate valve (big black plastic thing) and the large pipe either side. If you undo one (or both) of the hose clamps you can see the valve itself (it may simply be stuck). If you then adjust the aircon you should be able to see the valve itself move.
If not it could well be the motor that has siezed or died (I took the motor on mine apart to try to fix but ended up buying a new one).
Have fun.
Steve
sfl993t4 said:
From memory, (mine was the passenger side, but I'm sure that its much the same).
There are two pipes (one on each side)that run from the rear of the car to the front carrying hot air forward. The amount of hot air on each side is controlled by a valve (so theoretically I guess that the 993 could have a split aircon system with different temps for driver and passenger if the controller was up to it).
If you take look in the footwell, there is a panel in the front outside corner which covers the valve and pipe carrying the hot air. I think that the panel is only held on by a couple of screws.
Once you've got the panel off, you can see the gate valve (big black plastic thing) and the large pipe either side. If you undo one (or both) of the hose clamps you can see the valve itself (it may simply be stuck). If you then adjust the aircon you should be able to see the valve itself move.
If not it could well be the motor that has siezed or died (I took the motor on mine apart to try to fix but ended up buying a new one).
Have fun.
Steve
Thanks Steve,There are two pipes (one on each side)that run from the rear of the car to the front carrying hot air forward. The amount of hot air on each side is controlled by a valve (so theoretically I guess that the 993 could have a split aircon system with different temps for driver and passenger if the controller was up to it).
If you take look in the footwell, there is a panel in the front outside corner which covers the valve and pipe carrying the hot air. I think that the panel is only held on by a couple of screws.
Once you've got the panel off, you can see the gate valve (big black plastic thing) and the large pipe either side. If you undo one (or both) of the hose clamps you can see the valve itself (it may simply be stuck). If you then adjust the aircon you should be able to see the valve itself move.
If not it could well be the motor that has siezed or died (I took the motor on mine apart to try to fix but ended up buying a new one).
Have fun.
Steve
I'll take a look and come back with (hopefully) some good news.
There's also some decent info at http://www.porsche964.co.uk/technical/servos.htm
phelix said:
There's also some decent info at http://www.porsche964.co.uk/technical/servos.htm
Phelix,thanks for the link, though it's for a 964 instead of a 993 it may be useful for diagnosing the problem.
The heating and ventilating system in the 993 is identical to the 964.
The common problem with heat in the footwell is the disintegration of the corregated paper tubes in the side trim which route the heated air from the side sills up into the left and right mixing chambers.
If there are any leaks in the tubes the hot air gets directed up to the underneath of the dash and makes the footwell very uncomfortable.
To the best of my knowledge there are no fans in the footwell area - only the two fans in the HVAC unit at the rear of the luggage compartment. The air mix in the mixing chambers is controlled by the flaps operated by the servo motors - also at the back of the luggage compartment. Servos also control the flow to the dash and footwell vents. In all there are 5 servo motors and the Technical Section on John Miles web site (referenced above) also contains details on the overhaul and repair of those motors.
Regards
Dave
The common problem with heat in the footwell is the disintegration of the corregated paper tubes in the side trim which route the heated air from the side sills up into the left and right mixing chambers.
If there are any leaks in the tubes the hot air gets directed up to the underneath of the dash and makes the footwell very uncomfortable.
To the best of my knowledge there are no fans in the footwell area - only the two fans in the HVAC unit at the rear of the luggage compartment. The air mix in the mixing chambers is controlled by the flaps operated by the servo motors - also at the back of the luggage compartment. Servos also control the flow to the dash and footwell vents. In all there are 5 servo motors and the Technical Section on John Miles web site (referenced above) also contains details on the overhaul and repair of those motors.
Regards
Dave
computamedic said:
The heating and ventilating system in the 993 is identical to the 964.
The common problem with heat in the footwell is the disintegration of the corregated paper tubes in the side trim which route the heated air from the side sills up into the left and right mixing chambers.
If there are any leaks in the tubes the hot air gets directed up to the underneath of the dash and makes the footwell very uncomfortable.
To the best of my knowledge there are no fans in the footwell area - only the two fans in the HVAC unit at the rear of the luggage compartment. The air mix in the mixing chambers is controlled by the flaps operated by the servo motors - also at the back of the luggage compartment. Servos also control the flow to the dash and footwell vents. In all there are 5 servo motors and the Technical Section on John Miles web site (referenced above) also contains details on the overhaul and repair of those motors.
Regards
Dave
Dave,The common problem with heat in the footwell is the disintegration of the corregated paper tubes in the side trim which route the heated air from the side sills up into the left and right mixing chambers.
If there are any leaks in the tubes the hot air gets directed up to the underneath of the dash and makes the footwell very uncomfortable.
To the best of my knowledge there are no fans in the footwell area - only the two fans in the HVAC unit at the rear of the luggage compartment. The air mix in the mixing chambers is controlled by the flaps operated by the servo motors - also at the back of the luggage compartment. Servos also control the flow to the dash and footwell vents. In all there are 5 servo motors and the Technical Section on John Miles web site (referenced above) also contains details on the overhaul and repair of those motors.
Regards
Dave
After reading a contribution on rennlist I thought the 993 had just 3 servos.
"(There are 3 servos on a 993, one to open/close footwell output, one to open close windshield output, one to open close fresh air input.) 964's have 2 more to control temp mixers. 993 temp mixer servos are in cabin under door sill trim area."
However, your comments on the corrugated paper tubes sounds like my problem, though it is difficult to pin it down exactly as we were trying to concentrate on getting home without passing out from heat overload... it's a little confusing pinning down the problem exactly because of the various slider control and vent permutations, it seemed like we had hot air blasting out just about everywhere, though the drivers foot well was most definitely hotter than my passenger's side. we had to devise an intricate door window/sunroof configuration that created a dyson-like vacuum effect expelling hot air out of the cabin faster than the wonky vents could breathe it out. your post has given me more hope that the problem will be straightforward to rectify, once I work out what the central cause is.
thanks.
Edited by Police State on Monday 20th August 21:27
Well, I managed to seperate the corrugated tube and the temperature mixing valve, and can now see that the mixing valve is stuck open which is allowing the exchanged heat from the exhaust to toast the cabin area, and no amount of messing with the heater controls/or AC will make it close. My question is, does anyone know which one of the 3 servos in the luggage compartment control the motor for this flap, or if indeed it is likely to be the servo, or something else?
ADDLED said:
Couldnt you just take the fuse out to stop the heater motor?
I can turn the heater motor on/off with the rotary controller. The problem is that the air duct that feeds the cabin (from the rear heat exchangers) still dumps very hot air into the cabin because the main ducting flap is stuck open. I actually want to fix the problem (as opposed to just stopping it), and wanted to isolate which part has given up. The servo controller in the bonnet area or the motor attached to the flap in the footwell recess.
smtk said:
I found turning on the recirculation stopped the air from coming in
sounds interesting... though on 2nd thoughts I'm not sure that will make a difference because the temperature mixing valve that sits between the hose in (from heat exhangers) and hose up (that feeds the plumbing behind the dash) is stuck on open.Police State said:
ADDLED said:
Couldnt you just take the fuse out to stop the heater motor?
I can turn the heater motor on/off with the rotary controller. The problem is that the air duct that feeds the cabin (from the rear heat exchangers) still dumps very hot air into the cabin because the main ducting flap is stuck open. I actually want to fix the problem (as opposed to just stopping it), and wanted to isolate which part has given up. The servo controller in the bonnet area or the motor attached to the flap in the footwell recess.
regds
ADDLED said:
Police State said:
ADDLED said:
Couldnt you just take the fuse out to stop the heater motor?
I can turn the heater motor on/off with the rotary controller. The problem is that the air duct that feeds the cabin (from the rear heat exchangers) still dumps very hot air into the cabin because the main ducting flap is stuck open. I actually want to fix the problem (as opposed to just stopping it), and wanted to isolate which part has given up. The servo controller in the bonnet area or the motor attached to the flap in the footwell recess.
regds
Looking at http://www.porsche964.co.uk/technical/servos.htm it looks like servo 2 or 4 is no longer functioning as it should. Not sure if they're different left and right; can you swap them round and see if the problem switches sides? If it switches that suggests it's the servo; if it doesn't switch that suggests it's the controlling circuit or something else.
Edited by phelix on Sunday 9th September 15:17
phelix said:
Looking at http://www.porsche964.co.uk/technical/servos.htm it looks like servo 2 or 4 is no longer functioning as it should. Not sure if they're differnt left and right; cab you swap them round and see if the problem switches sides? If it switches that suggests it's the servo; if it doesn't switch that suggests it the controlling circuit or something else.
Phelix, I like that idea. I'll give it a try... thing is though, the 993 has only 3 servos in the luggage bulkhead, i believe the other two are in the engine bay. So i will still have to figure out which does what. I have the 993 repair manual and the PET catalogue on CD, but it makes no mention of the servos in either publication. Does anyone know what each servo in the 993 luggage area does?
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