PTC heater retrofit guide

A

a-zwo

Well-Known Member
I thought it would be a good challenge to fit the PTC heater to a petrol and that I might as well make a guide as I go along :)
1736112986951.jpeg

PTC?
Is an electric heating element that was fitted to late diesel A2’s sold in cold climates, and some earlier A2’s. It directly heats the cabin air, compared to a Webasto that heats coolant. They were never fitted to petrol vehicles as they were “not required”
They are available in 900 watt and 1500 watt variants and both can be fitted using this guide.
When the outside temperature is below a threshold, ECON is off, the battery voltage is stable and the alternator load is below a threshold, the PTC turns on to heat up the cabin air faster.

For the 900 watt version, at 0 degrees ambient, you have 20+ degree air coming from the vents within 2 minutes, so it is very effective.

Control
On diesel vehicles, the PTC and Webasto are controlled by the ECU. As they were never an option for petrols, there is no provision for control on the petrol ECU’s.
So there are 3 options for control:
- Add a aftermarket switch to the dash
- Intercept the heater signal with an additional CAN bus module (Color MFA, etc.)
- Add custom code to the ECU to control the heater

I will be doing option 3 but I will include instructions for the other 2 options too. Option 3 will only work for 1.4 petrols with Climatronic, it could be made to work on FSI’s and non-climatronic cars too if there was considerable interest.

Cost & Difficulty
Most of the parts can be had second hand for a very low cost, the PTC, relay holders and connectors were used across the VAG range for many years.
It is not very difficult, but it’s time consuming. The centre console and lower dash pieces in the footwell have to be removed, the ESP sensors and some of the lower dash structure.

More coming soon :)
 
After some more research, I have 2 found more PTC variants.

These are used on the 6Y Fabia and the 6R Polo.

There are no official wattage figures for these, but based on some measurements, I know the Fabia part to be around 500/600 Watts, probably peaking at 700 Watts in very cold conditions.

These are the part numbers. I am 99% sure the Fabia part and the 900 watt A2 part are the same, but the Fabia part is cheaper and more available.

I think the Fabia and Polo parts are also the same power, but the Polo part has extra mesh to force more air through the element.

A2 900 Watt: 8Z0819011
A2 1500 Watt: 8Z0819011A
Fabia: 6Q0963235B
Polo: 6R0963235
 
a-zwo said:
After some more research, I have 2 found more PTC variants.

These are used on the 6Y Fabia and the 6R Polo.

There are no official wattage figures for these, but based on some measurements, I know the Fabia part to be around 500/600 Watts, probably peaking at 700 Watts in very cold conditions.

These are the part numbers. I am 99% sure the Fabia part and the 900 watt A2 part are the same, but the Fabia part is cheaper and more available.

I think the Fabia and Polo parts are also the same power, but the Polo part has extra mesh to force more air through the element.

A2 900 Watt: 8Z0819011
A2 1500 Watt: 8Z0819011A
Fabia: 6Q0963235B
Polo: 6R0963235
Click to expand...
Might these be more suitable for cars with smaller alternators than the Tdi 140A (ie, the 110A 1.6 alternator that can be exchanged onto the 1.4i with a 90A alternator to begin with?) - bearing in mind issues encountered with "brown outs" on tired alternators (ie various ECU fault codes and steering drop out just after starting when battery not 100%) I suspect that the 90A one on our 1.4i would be at crisis point with the bigger ones, and possibly even these slightly lighter loads. Certainly interesting, though.
 
Well what is the point of it on gasoline when within 2 minutes there is warm air coming from the heater when idling? 🤔

I was thinking yesterday about PTC heater on my TDI and I would be glad if it did bypass heater matrix until coolant temp reaches 70-80°C. Currently it blows through the cold heater matrix further cooling down the engine. In ideal world it would help warm up the engine (not taking any heat from coolant during cold start) and blow warm air into the cabin.
 
Because it’s still faster, you get the heat level in less than 2 minutes that would take between 5 and 10 minutes without.
So it makes quite a large difference to the defrosting speed.

Plus, I just like to see what’s possible! :D

That would be good, but I think the PTC was probably a bit of an afterthought anyway
 
The current cold snap had me thinking along these lines for the petrol A2s.
Living 700ft above sea level in Scotland it seems like a worthwhile option.
My 2 litre diesel daily driver has a similar toaster style element in the heater box and has been invaluable in our current -3.5 mornings.
As a screen defroster to help remove the inch of frozen snow encasing the wipers without taking any heat from the engine it works very well.
Also helps clear the ice off the inside of the windscreen🥶

With regard to the battery drain, we have a portable cool box that incorporates a voltage sensor so it will not deplete the battery below a set level if you inadvertently left it connected.
Had also thought about a simple version with a timed switch similar to the rear defroster switch on my daily which seems to switch itself off after a set period as one A2 is the basic no aircon model.
 
I can only say the webasto heater is fabulous.
Just need some heated seats (heated steering wheel would also be nice....Tom?) also and perfect for winter..
 
I did check warm up time compared to petrol. The Webasto for cabin warmth is the quickest.
The Petrols with good thermostats are actually quite good also...no complaints on those.
Our Tdi with no additional heater is soooooo slooooow to warm up..
 
donp38 said:
Just need some heated seats (heated steering wheel would also be nice....Tom?) also and perfect for winter
Click to expand...
Evening Brian,

Agree that a heated steering wheel really is a nice thing, so far I’ve not taken the alcantara covering off the A4 B9 FBMFSW, just not brave enough as I’d hate to ruin the fabric. If I ever find a bargain equivalent though then I’ll happily take it apart and add the heating element to it.

Kind regards,

Tom
 
Yes that is why they weren’t fitted from the factory, they are quite good compared to the diesel but it can if course be faster :)

And battery drain will not be an issue with this, because the software will monitor the battery voltage and alternator load so that the elements are only turned on if there is enough energy.
 
Now I have confirmed the ECU control is possible, there are two spare outputs available on the ECU.

1736857401600.jpeg


This picture shows inside a 4MV, the highlighted chips are the input/output drivers.

Most of these parts are custom so there is no public information about them. Instead, I used a multimeter to check continuity between all of the external ECU pins and the pins of these drivers. Many of the pins are entirely unconnected, and the rest of them have functions that are described in the wiring diagram.

There are however 2 pins that are not assigned, connected to the yellow chip. I do not know what they were originally for, but they are available on both 4LV and 4MV ECU’s. I will use these pins to control the heater. You could also use them for Turbo control if you wrote the code for it.

There are also several other pins available that can be used as inputs.
 
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