# Understanding the "Residual Heat" function



## PanEuropean (Nov 3, 2001)

I never claimed to be 'the first dog off the porch' when it comes to understanding how things work, but equally, I don't think I'm stupid, either. So, after reading the Phaeton owner's manual a few times, and spending a few evenings in the garage (after dinner) trying to figure out how all the buttons worked, I came to the conclusion that my car did not have the "Residual Heat" feature that is described on page 25 of booklet 3.1.2. The reason I concluded that the car did not have this feature was because the "Residual Heat" menu choice was always dimmed out, just like the "Solar Ventilation" choice above it. I *know* I don't have a sunroof with solar power cells in it, so I figured that if Residual Heat was also dimmed out all the time, I probably didn't have it, either.
Wrong. My car does have the residual heat circulation feature, the problem is that VW does a very poor job of explaining how to use this system in the owner manual.
The Residual Heat feature will operate a small water pump in the engine cooling system to circulate warm water through the heater core in the passenger cabin for up to 30 minutes after the car has been turned off. The idea is that this will keep your car nice and warm on those cold January nights while you are waiting in the lineup at the Blockbuster to check out your movie, and your car is sitting in the parking lot outside.
It stands to reason (well, at least, looking at it retrospectively, anyway) that if there ain't no heat in the engine to recirculate, it doesn't make much sense to offer this feature, right? What I was doing the first few days I had the car was going down to the garage to figure out all the features, bells and whistles, after the car had been parked in the garage for an hour or so. After an hour or so, there was no heat left in the engine, so, the car dimmed out this particular choice.
Today, quite by accident, I got into that same menu page on the infotainment system after pulling off the expressway, following a one hour drive (= hot engine), and "Residual Heat" was available as a menu choice.
Note that if 'Automatic Recirculation' is available as a menu choice (condition = engine running), then 'Residual Heat' will not be available. By the same token, if 'Residual Heat' is selected (active), then 'Automatic Recirculation' will be unavailable (dimmed out). The two choices are mutually exclusive. Residual Heat is only available as a menu choice when the following conditions have been met: 1) Engine is turned off, and; 2) Engine coolant has reached normal operating temperature. The two photos below illustrate this.
Hope this information is useful to others in the future. I also hope that if there are any 'lurkers' from VWoA, or Dresden who read this, that you give consideration to improving the message on the infotainment display to explain *why* residual heat is not available - e.g "Residual Heat Not Available - Engine Running", or "Residual Heat Not Available - Coolant Temperature Too Low."
PanEuropean
*Residual Heat available as a menu choice, and selected 'on'*
_*Prerequisites:* Engine off, engine coolant at normal operating temperature._








*Residual Heat not available as a menu choice*
_*Possible reasons why:* Engine is running, or coolant is not yet reached full operating temperature, or car has been turned off for a while and coolant temperature has started to decline._


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## rjlvw (May 13, 2004)

*Re: Understanding the "Residual Heat" function (PanEuropean)*

I too was under the impression that the residual heat function was not available on my V8. I think I was trying to access the function while the engine was running like I believe you could do in my Touareg. Someone else posted a while back that the trick is to shut off the car, but do not remove the key. Sure enough it works. I don't think it matters whether the engine is warm or cold for the function to be accessible - I'm pretty sure I was just trying it out with a dead cold engine in the garage. I'll have to double check for sure once the car gets back from the bodyshop. Obviously, if you activate the function when the engine has not been running for long, there won't be much residual heat to circulate.


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## Corradodrvrfnd (Feb 15, 2002)

*Re: Understanding the "Residual Heat" function (rjlvw)*

I was also confused, as in the Touareg you just hit the button after turning the car off.
Thanks for the imformative post, as always, paneuropean.


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## PanEuropean (Nov 3, 2001)

*Re: Understanding the "Residual Heat" function (rjlvw)*


_Quote, originally posted by *rjlvw* »_ ...I don't think it matters whether the engine is warm or cold for the function to be accessible...

I haven't had enough experience using it to be able to say with certainty whether the engine needs to be at normal operating temperature before the "residual heat" choice becomes available or not - but it makes sense to me, just from a programming and logic point of view, that the ability to enable residual heat should be dimmed out if there is not enough heat present in the engine coolant to actually do any good.
Based on what I know now (one week's experience), it seems that the engine needs to be warm enough to actually be able to supply heat to the cabin before the choice becomes enabled (i.e. not dimmed out) on the infotainment menu.
PanEuropean


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## PanEuropean (Nov 3, 2001)

*Re: Understanding the "Residual Heat" function (trekguy)*

All North American Phaetons have two batteries, one that is dedicated to cabin systems, and another that is dedicated to starting the engine. The residual heat system uses the cabin systems battery - so, assuming the car is in good working order, the residual heat function should always be available, assuming the coolant is warm enough.
PanEuropean


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## PanEuropean (Nov 3, 2001)

*Re: Understanding the "Residual Heat" function (rmg2)*

Hi All:
I finally got the residual heat feature figured out - by that I mean I now know how to turn it on without difficulty:
*1)* You need warm coolant. The car makes its own decision about whether the coolant is warm enough. The electrical system must also be in 'normal operation' mode, by this I mean no fault conditions exist that have put the car into 'automatic load shedding' mode. 
*2)* Shut off the engine, but do not open any of the doors (as long as you have not opened a door, the big central control screen - the J523 - remains powered, and you can access all the functions on it.
*3)* Press the CLIMATE button on the infotainment system, then press the 'OTHER FUNCTIONS' softkey. There should now be a little vertical bar visible in the screen beside the 'RESIDUAL HEAT' softkey. Press the 'RESIDUAL HEAT' softkey, this vertical bar will fill in with a yellow colour. The residual heat function is now enabled. The visual feedback that you get, to indicate that it is working, is that some of the temperature control lights above the infotainment screen will now illuminate - for example, if the system was in AUTO mode before you turned it off, the AUTO mode light(s) will re-illuminate.
*4)* It will run either for half an hour, or until the coolant temperature drops to the point where there is no longer any heat left to be extracted, or until the voltage level in the onboard power supply battery drops to the first load shedding threshold. 
This system uses power from the onboard power supply battery only, never from the starter battery. Therefore, no concerns about cranking power available to start the engine next time you want to use the car.
Michael


_Modified by PanEuropean at 6:00 PM 12-29-2005_


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## Razlaw (Apr 24, 2004)

thanks for the posts on residual heat did not think my card had it but tried it after letting car warm up and there it was.


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## PanEuropean (Nov 3, 2001)

*Re: (cgmb16)*

The Phaeton manages the residual heat function through the automatic mode by default. I have not checked to see if the user can 'fine tune' it by switching over to manual mode.
At first glance, it seems to me to be kind of pointless to want to manually control this function - the residual heat function is there to keep the car warm when you are not in it - if you are in it, and you want warm (or cool) air, you just start the car and operate the climate system as you wish.
If you are not in the car, then it only makes sense to have the residual heat distribution automatically controlled, so that the humidity sensor keeps the windshield clear of condensation.
Michael


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## PanEuropean (Nov 3, 2001)

*Re: (cgmb16)*

Oh, sorry, I didn't mean to sound ungrateful - I was just trying to think critically about use of the residual heat function when the car was occupied, or during the summer.
For summer cooling, we use the solar powered sunroof, it generates its own electricity to run the cabin ventilation fan, and keep the interior cool. I guess that's why using the residual heat function didn't ring any bells with me.
Michael
*Solar Cells in Phaeton Sunroof*


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## PanEuropean (Nov 3, 2001)

*Re: (PanEuropean)*

Finally had a chance to use the Residual Heat function on a really cold and snowy day today. Here's the really short and concise operating instructions:
*1)* Turn the engine off, but do not turn the ignition off (in other words, just move the key fractionally counter-clockwise until the engine stops) *OR* turn the engine off and take the key out, but do not open any door on the car until you accomplish step 2, below.
*2)* Press CLIMATE, then "Other Functions", then press "Residual Heat".
*3)* Take the key out and go do your thing.
Michael
NB: A bit of a software snag in the car - if you have "Automatic Recirculation" enabled, turning on Residual Heat will disable it, and that will persist across start cycles. So, if you want Automatic Recirculation back on again, you have to turn it on manually following each use of the residual heat function. I can comprehend why Automatic Recirculation has to be off when Residual Heat is being used, but it seems to me to be sloppy software programming to allow a one-time use of Residual Heat to cause a persistent change in the Automatic Recirculation feature.
Guess we'll all have to wait for "Phaeton Service Pack 1" to come out on CD...










_Modified by PanEuropean at 6:01 PM 12-29-2005_


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## dadler (May 14, 2005)

*Re: Residual Heat Option or standard? (PanEuropean)*

Well it works! Residual heat works. I am surprised that this is not an option to "leave on" but must be reset everytime the car is turned off. As I understand the function Ii must remember to put on residual heat everytime I want to have the car keep the temperature at the preset level. Why not make this an option that stays on until summer when i would turn it off?


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## dadler (May 14, 2005)

Short trips on cold days is exactly the nice time to have residual heat in the car. Think those smart engineers could keep a battery alive with a shutoff on low power. Maybe link the blower to the solar power?


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## PanEuropean (Nov 3, 2001)

*Re: (dadler)*


_Quote, originally posted by *dadler* »_Maybe link the blower to the solar power?

Good idea, David, but the residual heat function requires a lot more electrical power than the solar powered ventilation function - which is a totally different option.
For solar powered ventilation, the only electrical consumer is the blower motor. There is no problem if it shuts on and off, for example, as a cloud passes overhead. Plus, this system is designed to get rid of heat buildup as a result of solar heating - so if it is a cloudy day, meaning not enough sunlight to power the panels, there is also not enough sunlight to heat up the cabin, so no problem.
For residual heat, you need to power quite a few other components - the blower motor (at a steady speed), the run-on electrical coolant circulation pump, some coolant valves, and the coolant temperature monitoring system. I don't think the solar panels in the solar sunroof would generate enough electricity to do this.
The two systems operate separately from each other - one can be installed, and the other not.
The very best solution would be the Webasto Auxiliary Stand-Heating System, which is available as a factory installed option outside of North America. This little furnace uses fuel from the vehicle tank - about half a liter, or 1/8th of a gallon an hour - to heat the coolant for both the engine and cabin heating. You can program it to come on at a certain time (like a coffeemaker) from the Central Control Screen on the Phaeton, or, you can control it with a remote on your key fob from up to 500 meters (yards) away. It does require electricity from the car, about the same amount as residual heat, but it will run for longer than the 30 minutes allowed for residual heat, and it can be used to heat a stone-cold car up to a nice temperature before you get into it.
It is not offered in North America out of fear that drivers would turn it on while the car is in an indoor garage, thus creating a great risk of carbon monoxide poisoning. It is very popular in Northern Europe (Scandinavia).
Michael


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## PanEuropean (Nov 3, 2001)

*Re: Understanding the "Residual Heat" function (PanEuropean)*

Photos re-hosted (just in time for the cold snap...)








Michael


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## unclepugh (Nov 7, 2008)

*Re: Understanding the "Residual Heat" function (PanEuropean)*

ok, having read all of the above, I still can't can't get it to work on my car. Was it standard or an option. Is there any way to tell if one has it other than it's working or not?
My car is an '06 with C&C and tech.
Thanks
Rick


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## HunterST (Dec 11, 2008)

*Re: Understanding the "Residual Heat" function (unclepugh)*

I believe it is part of the cold weather package.


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## HunterST (Dec 11, 2008)

*Re: Understanding the "Residual Heat" function (unclepugh)*

I believe it is part of the cold weather package.


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## derrickonline (Feb 9, 2008)

*Re: Understanding the "Residual Heat" function (PanEuropean)*

I'm really digging this residual heat feature. Ever since car_guy posted about it....I've been using it. Niiiiiiic. Now I can leave my guest in the car warm while I run into the store and not have to worry about leaving my car running or leaving the keys in the car.


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## unclepugh (Nov 7, 2008)

*Re: Understanding the "Residual Heat" function (HunterST)*

but I have the cold and comfort package and it still doesn't work. Is residual heat on everybody's screen (climate/other functions) or only if installed?


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## derrickonline (Feb 9, 2008)

*Re: Understanding the "Residual Heat" function (unclepugh)*

I'm not positive, I thought everyone had it. I do know I have the hot/cold package so you should have it... here's what to do.
Click Climate
Click Other options (I'm working off memory)
Bottom right of the screen should be residual heat.
The car must be in the off positon I believe. Once the car is off (and the car is aready warm) put on the residual heat, take your keys out and get out of the car (if you want).


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## unclepugh (Nov 7, 2008)

*Re: Understanding the "Residual Heat" function (derrickonline)*

AH HAH it works now


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## PanEuropean (Nov 3, 2001)

Photos re-hosted (just in time for winter!).

Michael


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## nshirazi1 (Sep 20, 2012)

Just ran accross this thread today and was very delighted to find out about the residual heat feature. I never really tried to figure it out before but now that I know I have it, I'm sure ill give it a shot. 
Thank you for the posts. Very informative. 
Nick


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## PanEuropean (Nov 3, 2001)

Hi Nick:

Glad to hear that the information is of use to you. In fact, in Overland Park, it will probably be of use to you for at least 6 months of the year... 

It's interesting to note that the greater Kansas City area was the second largest market for Phaetons in the USA, second only to Chicago. I remember going to quite a few Phaeton owner Get-Togethers in the KC area - specifically, Olathe and Overland Park.

Michael


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## nshirazi1 (Sep 20, 2012)

PanEuropean said:


> Hi Nick:
> 
> Glad to hear that the information is of use to you. In fact, in Overland Park, it will probably be of use to you for at least 6 months of the year...
> 
> ...


Youre not kidding, its already getting cold here. i just sat in my garage tested the feature which was very nice.
I would have never guessed the KC market being the second largest. I would love to meet up with other owners but haven't seen one here at all. Do you know if people meet up any more? I'm a fairly new owner and am sold for life. Would love to find out if there are any more get-togethers. 

Thanks again, 
Nick


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## n968412L (Apr 23, 2009)

Been an enthusiastic user of this facility for three winters now.
Be interested in others' experiences. I find it only runs for about 20 minutes from a hot engine. I suppose it could be the battery... but LH batteries in my fleet are scrupulously maintained - some of them by experts (H!). Most of my experience is with the V6 as that is the winter car of the fleet...... but now I've bought another set of wheels and winter tyres for the V10... I'll report on that one too.

And not sure it's coolant temperature decline, because when I come to restart the coolant often has only dropped 10°C to about 80°C.

So - I'd be interested to see how long others manage to enjoy residual heat for.

Regards

M


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## PanEuropean (Nov 3, 2001)

n968412L said:


> I find it only runs for about 20 minutes from a hot engine.


That's more or less my experience as well - in my case, with the W12 engine, it runs for about 30 minutes.

I kind of suspect that the design intent of the system is to prevent snow from building up on the windows, or to prevent condensation from forming on the inside of the glass while the driver is running a short errand - ducking into the local grocery store, filling the fuel tank, etc.

For any longer periods of time, there is an independent supplemental heater option (the Webasto supplemental heater). That option was not offered in North America.

Michael


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## Gabs08PHTN (Jan 6, 2011)

Hi all,
My previous car, a Volvo XC 70 featured likewise the supplementary heater and the residual heat function. Funny enough the residual heat lasted for 20 minutes too.
So I wonder if it has something to do with a preset program within the supplementary heater control unit that runs the pump for 20 minutes regardless of the car model or manufacturer.
Cheers.

Gabriel


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## n968412L (Apr 23, 2009)

PanEuropean said:


> For any longer periods of time, there is an independent supplemental heater option (the Webasto supplemental heater). That option was not offered in North America.


Oh yes - one of the few advantages of being in Europe - I think all the diesel GP0 and GP1 have them.

Lovely!

M


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## ERphaeton (Jan 30, 2016)

*Warm air with AC Off*

Hi PanEuropean and guys 

I'm experiencing a strange phenomenon. Air Conditioning is set to OFF in the car (2007 Phaeton V6 3.0 TDI) but strangely the car gets warm. After I inspected I realized the warm air is coming from the upper air flows (just under the windshield). The flow is quite light but warm. The outside temperature was 9 degrees Celcius, but the car was getting really warm without switching on the A/C. 
Have you ever experienced something like this. 
All the functionalities of the AC are perfect, so it warms in cold weather and it cools in hot weather perfectly. 
Please advice... Thank you in advance! 




PanEuropean said:


> _Quote, originally posted by *rjlvw* »_ ...I don't think it matters whether the engine is warm or cold for the function to be accessible...
> 
> I haven't had enough experience using it to be able to say with certainty whether the engine needs to be at normal operating temperature before the "residual heat" choice becomes available or not - but it makes sense to me, just from a programming and logic point of view, that the ability to enable residual heat should be dimmed out if there is not enough heat present in the engine coolant to actually do any good.
> Based on what I know now (one week's experience), it seems that the engine needs to be warm enough to actually be able to supply heat to the cabin before the choice becomes enabled (i.e. not dimmed out) on the infotainment menu.
> PanEuropean


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