Does anyone really REALLY understand the heating system?
Thread Starter
Three Wheelin'
Joined: Dec 2006
Posts: 1,506
Likes: 0
From: Texas
Does anyone really REALLY understand the heating system?
I have mentioned going no heat at all but am still wavering.
Another thought is to remove the rear blowers and bypass them with a tube. Still have some heat but may not blow as hard.
However, I have read on the 964 board about issues getting things to work correctly (front fan speed, etc.) with the rear blowers out. I think there are resistors needed to trick the system when doing the heater bypass.
I have also read about the rear blowers helping cool the car at lower speed. I kind of doubt that theory since the air is taken right after the fan which doesn't allow the air to cross over the engine before pulling it away.
I would appreciate anyones thoughts, ideas and experience.
Thanks.
RT
Another thought is to remove the rear blowers and bypass them with a tube. Still have some heat but may not blow as hard.
However, I have read on the 964 board about issues getting things to work correctly (front fan speed, etc.) with the rear blowers out. I think there are resistors needed to trick the system when doing the heater bypass.
I have also read about the rear blowers helping cool the car at lower speed. I kind of doubt that theory since the air is taken right after the fan which doesn't allow the air to cross over the engine before pulling it away.
I would appreciate anyones thoughts, ideas and experience.
Thanks.
RT
Three Wheelin'
Joined: Apr 2006
Posts: 1,977
Likes: 0
From: London, England
RT,
Sorry to be negative but apart from the myriad of electronic control boxes on the 965, the heating system is probably the most feared part and little understood (despite most garages telling you otherwise) of these cars.
Speaking from experience, the 964 heating is (too) complex. I had permanent heat, failed aircon, misdirected heat and so on. I spent loads £££ with several different garages on rebuilding and replacing. We replaced various servos, flaps, pipes, even the cabin control unit (new one from Porsche and several 2nd hand) and don't even get me started on the aircon. After all this, the scariest was when I had a discussion with one about the possibility that the 'heart' of the heating system known as the 'heater matrix' (!) which is hardly ever mentioned, might need replacing. You try to find it on the Porsche price list and just look at the price (is it still available?). AND its situated way down in the front, tank out etc. etc.
Most of the 965 guys I know have heating that doesn't work correctly, or at all.
RT, I'd say try your own fixes, you'll probably do a better job than 99% of the 'experts'.
Sorry to be negative but apart from the myriad of electronic control boxes on the 965, the heating system is probably the most feared part and little understood (despite most garages telling you otherwise) of these cars.
Speaking from experience, the 964 heating is (too) complex. I had permanent heat, failed aircon, misdirected heat and so on. I spent loads £££ with several different garages on rebuilding and replacing. We replaced various servos, flaps, pipes, even the cabin control unit (new one from Porsche and several 2nd hand) and don't even get me started on the aircon. After all this, the scariest was when I had a discussion with one about the possibility that the 'heart' of the heating system known as the 'heater matrix' (!) which is hardly ever mentioned, might need replacing. You try to find it on the Porsche price list and just look at the price (is it still available?). AND its situated way down in the front, tank out etc. etc.
Most of the 965 guys I know have heating that doesn't work correctly, or at all.
RT, I'd say try your own fixes, you'll probably do a better job than 99% of the 'experts'.
Thread Starter
Three Wheelin'
Joined: Dec 2006
Posts: 1,506
Likes: 0
From: Texas
Thanks for the response. From what I can tell the system is pretty much crap.
I am leaning more toward junking it. Being in Texas, it isn't cold that often. I'll get it working and then probably have something else break. I don't like the exhaust smell in the cabin you get with any leak (though I am replacing headers).
My biggest concerns are (in order):
A) engine cooling diminishment
B) impact on front blowers with the rears removed
C) fogging up due to humidity (though may be workable with AC)
D) loss of heat in cold
I like the idea of less weight on the *** end too.
Oh and I am the only one that touches this car...except for some specialized work such as rollbar fab, engine machining and the likes.
Thanks.
RT
I am leaning more toward junking it. Being in Texas, it isn't cold that often. I'll get it working and then probably have something else break. I don't like the exhaust smell in the cabin you get with any leak (though I am replacing headers).
My biggest concerns are (in order):
A) engine cooling diminishment
B) impact on front blowers with the rears removed
C) fogging up due to humidity (though may be workable with AC)
D) loss of heat in cold
I like the idea of less weight on the *** end too.
Oh and I am the only one that touches this car...except for some specialized work such as rollbar fab, engine machining and the likes.
Thanks.
RT
Instructor
Joined: Jul 2007
Posts: 127
Likes: 1
From: Pleasanton, CA
I "backdated" my heating a few weeks ago... permanent results pending. It was great pulling out those stupid heavy fans from the fenders and all the plumbing. The most un-fun part was cutting a hole in the rightside tin. I actually bought a used old-style tin but it didn't fit right with the other tins so I ended up cutting my original and running old-fashioned OEM piping straight to the heat exchangers.
My heat and defrost work fine, and I didn't have to put resistors on the fan plugs or anything. I've also been stuck in traffic and the motor didn't Chernobyl.
I won't advocate anyone to do as I've done as many of my mods are an ongoing experiment and I recognize the potential consequences for ignorantly or recklessly modifying an OEM system.
If this mod turns out to be acceptable for the long-term I will at some point either bypass and remove or at least disable those flow bypass flaps (described in Adrian's book) that CLANK annoyingly every time I close the door.
My heat and defrost work fine, and I didn't have to put resistors on the fan plugs or anything. I've also been stuck in traffic and the motor didn't Chernobyl.
I won't advocate anyone to do as I've done as many of my mods are an ongoing experiment and I recognize the potential consequences for ignorantly or recklessly modifying an OEM system.
If this mod turns out to be acceptable for the long-term I will at some point either bypass and remove or at least disable those flow bypass flaps (described in Adrian's book) that CLANK annoyingly every time I close the door.
Rennlist Member
Joined: Oct 2007
Posts: 2,127
Likes: 143
From: wash dc/ los angeles ca
Ryan and others....
1. your heat comes from a self contained box mounted on the header(heatexchange)
2. the engine cooling air is drawn from the outside pushed down through the cylinders and head
fins out the bottom of the car
3.any oil smell or burning is derived from engine oil or spillage onto headers etc
then pushed into interior through heated air in exchanger
4. the only fan on engine for heat is likely above and over manifold and simply
pushes air for added pressure in system
5. the 964/993 heat/ac system is heads and tails above anything porsche had
introduced in almost 15 years since the SC/Carrera days which was mostly earlier
911 archaic bits.
6. Most problems associated with this system either have to do with the control head
unit ,which can be switched out easily enough or the footwell blowers and flaps
that have a habit of failing should the car sit up or get moisture down the vents.
7. get those two items addressed and a good ac charge and you've really got a
car that can keep you comfortable,summer,spring and winter...
8 unless your really going full track assault,disabling your hvac function is just stupid,sorry....my 02 Bert
1. your heat comes from a self contained box mounted on the header(heatexchange)
2. the engine cooling air is drawn from the outside pushed down through the cylinders and head
fins out the bottom of the car
3.any oil smell or burning is derived from engine oil or spillage onto headers etc
then pushed into interior through heated air in exchanger
4. the only fan on engine for heat is likely above and over manifold and simply
pushes air for added pressure in system
5. the 964/993 heat/ac system is heads and tails above anything porsche had
introduced in almost 15 years since the SC/Carrera days which was mostly earlier
911 archaic bits.
6. Most problems associated with this system either have to do with the control head
unit ,which can be switched out easily enough or the footwell blowers and flaps
that have a habit of failing should the car sit up or get moisture down the vents.
7. get those two items addressed and a good ac charge and you've really got a
car that can keep you comfortable,summer,spring and winter...
8 unless your really going full track assault,disabling your hvac function is just stupid,sorry....my 02 Bert
Last edited by budge96; Feb 16, 2009 at 08:09 PM. Reason: correction
Rennlist Member
Joined: May 2001
Posts: 13,507
Likes: 834
From: Auckland, New Zealand.
Are there any relays in the control head unit? I ask because a problem in my turbocharger control unit was caused by a broken relay. I wonder how many boxes are swapped out for want of a $10 part.
Last edited by John McM; Feb 6, 2009 at 08:43 AM.
Rennlist Member
Joined: Oct 2007
Posts: 2,127
Likes: 143
From: wash dc/ los angeles ca
John, hats off to you, I read your post on that neat bit of surgery you did on the
turbo control unit...
I'd have to say your likely correct a lot of this technology is 15 or more years old and
the internal relays could easily have seen better days.
as you said many components switched out for want of a $10 part...I will say most of us don't have aircraft electronic level skill set when it comes to this sort of repair,
understanding it is difficult journey enough....Bert
turbo control unit...
I'd have to say your likely correct a lot of this technology is 15 or more years old and
the internal relays could easily have seen better days.
as you said many components switched out for want of a $10 part...I will say most of us don't have aircraft electronic level skill set when it comes to this sort of repair,
understanding it is difficult journey enough....Bert
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Thread Starter
Three Wheelin'
Joined: Dec 2006
Posts: 1,506
Likes: 0
From: Texas
I "backdated" my heating a few weeks ago... permanent results pending. It was great pulling out those stupid heavy fans from the fenders and all the plumbing. The most un-fun part was cutting a hole in the rightside tin. I actually bought a used old-style tin but it didn't fit right with the other tins so I ended up cutting my original and running old-fashioned OEM piping straight to the heat exchangers.
My heat and defrost work fine, and I didn't have to put resistors on the fan plugs or anything. I've also been stuck in traffic and the motor didn't Chernobyl.
I won't advocate anyone to do as I've done as many of my mods are an ongoing experiment and I recognize the potential consequences for ignorantly or recklessly modifying an OEM system.
If this mod turns out to be acceptable for the long-term I will at some point either bypass and remove or at least disable those flow bypass flaps (described in Adrian's book) that CLANK annoyingly every time I close the door.
My heat and defrost work fine, and I didn't have to put resistors on the fan plugs or anything. I've also been stuck in traffic and the motor didn't Chernobyl.
I won't advocate anyone to do as I've done as many of my mods are an ongoing experiment and I recognize the potential consequences for ignorantly or recklessly modifying an OEM system.
If this mod turns out to be acceptable for the long-term I will at some point either bypass and remove or at least disable those flow bypass flaps (described in Adrian's book) that CLANK annoyingly every time I close the door.
My new idea is to pull the air from the eingine compartment through a filter rather than from the air that passes directly by the engine. This might cut down a bit of the oil/fuel smells in the cabin.
Any idea on a filter that might work for this task?
Cheers.
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Thread Starter
Three Wheelin'
Joined: Dec 2006
Posts: 1,506
Likes: 0
From: Texas
Rennlist Member
Joined: Oct 2007
Posts: 2,127
Likes: 143
From: wash dc/ los angeles ca
Their are filters in the pathway of the heat you receive in cabin already..
Most of any fuel or oil smell is attributed to burnt oil /unburnt fuel(ie; rich)
remaining in your headers and going into the heatexchange boxes.
Best thing would be to check your header gaskets and and pooling of excess
fule or oil onto headers. no matter how small.
Also a rich as opposed to lean condition maybe caused by non functioning 02
sensors can create the same symptoms..
Most of any fuel or oil smell is attributed to burnt oil /unburnt fuel(ie; rich)
remaining in your headers and going into the heatexchange boxes.
Best thing would be to check your header gaskets and and pooling of excess
fule or oil onto headers. no matter how small.
Also a rich as opposed to lean condition maybe caused by non functioning 02
sensors can create the same symptoms..
Thread Starter
Three Wheelin'
Joined: Dec 2006
Posts: 1,506
Likes: 0
From: Texas
Instructor
Joined: Jul 2007
Posts: 127
Likes: 1
From: Pleasanton, CA
The air for the heating system originates from the engine compartment. Air is drawn in by the engine cooling fan and part of it is blown out the heater hose scoops on the sides of the fan. In the old days this air was directed straight down to the heater boxes, and the driver and passenger each had a lever adjacent the handbrake to operate valves that allowed this air to be routed to the cabin or exhausted to the wheelwells. Newer models simply appended this function with "helper" fan or fans in the back of the car to push heated airflow to the cabin when the engine fan is not moving a lot of air at low revs. All I did was remove this feature, and have found I get plenty of heated air anyway. There are no filters I'm aware of between the heater boxes and cabin. Secondly, since the air originates in the engine compartment you can smell a manifold boost leak or other fuel leak, as the cooling fan will draw these fumes and push them through the heater boxes and into the cabin.
Thread Starter
Three Wheelin'
Joined: Dec 2006
Posts: 1,506
Likes: 0
From: Texas
The air for the heating system originates from the engine compartment. Air is drawn in by the engine cooling fan and part of it is blown out the heater hose scoops on the sides of the fan. In the old days this air was directed straight down to the heater boxes, and the driver and passenger each had a lever adjacent the handbrake to operate valves that allowed this air to be routed to the cabin or exhausted to the wheelwells. Newer models simply appended this function with "helper" fan or fans in the back of the car to push heated airflow to the cabin when the engine fan is not moving a lot of air at low revs. All I did was remove this feature, and have found I get plenty of heated air anyway. There are no filters I'm aware of between the heater boxes and cabin. Secondly, since the air originates in the engine compartment you can smell a manifold boost leak or other fuel leak, as the cooling fan will draw these fumes and push them through the heater boxes and into the cabin.
I am having my buddy in automation look at the valve and see if we can rig up a small motor to control from the cabin via switch. I don't want any heat 95% of the time and the old-days system would have been a better choice for my needs (heat-wise).
Does the engine fan create much airflow through the heater tube scoops when there is no additional blower pulling? What do you think about pulling the air in from above the engine rather than the air coming through the fan/shroud and rely only on the front blowers to pull in the hot air?
Currently my engine has some decent oil on it that makes the fumes pretty noxious when it gets warm. I guess it can be used as an indicator of something working improperly back there.
My problem is that in 90 deg + Houston, any additional heating of the cabin is a bad thing.
RT
Instructor
Joined: Jul 2007
Posts: 127
Likes: 1
From: Pleasanton, CA
To my understanding, when you have the heat off, or in our case the t-stat **** is dialed to cooler temp than cabin temp, the ducts from the heaterboxes to the cabin are closed. In this case the air blown through the heaterboxes is simply dumped into the wheelwells and you are not getting any of it in the cabin.
That said, there IS a suplemental engine cooling function in this system. There is always air being blown through the heaterboxes, and it is designed as such to aide cooling the engine and exhaust manifold. I would NOT disable the air ducting from the fan shroud to the heater boxes unless you were going non-heat headers.
That said, there IS a suplemental engine cooling function in this system. There is always air being blown through the heaterboxes, and it is designed as such to aide cooling the engine and exhaust manifold. I would NOT disable the air ducting from the fan shroud to the heater boxes unless you were going non-heat headers.
Thread Starter
Three Wheelin'
Joined: Dec 2006
Posts: 1,506
Likes: 0
From: Texas
To my understanding, when you have the heat off, or in our case the t-stat **** is dialed to cooler temp than cabin temp, the ducts from the heaterboxes to the cabin are closed. In this case the air blown through the heaterboxes is simply dumped into the wheelwells and you are not getting any of it in the cabin.
That said, there IS a suplemental engine cooling function in this system. There is always air being blown through the heaterboxes, and it is designed as such to aide cooling the engine and exhaust manifold. I would NOT disable the air ducting from the fan shroud to the heater boxes unless you were going non-heat headers.
That said, there IS a suplemental engine cooling function in this system. There is always air being blown through the heaterboxes, and it is designed as such to aide cooling the engine and exhaust manifold. I would NOT disable the air ducting from the fan shroud to the heater boxes unless you were going non-heat headers.
My thought around the supplemental engine cooling is that it isn't doing much. The air comes in from the fan and immediately routed to the blower/heat exchanger. If the duct was on the other end of the engine, I would definitely think so.
