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Premium Member
174 Posts
Discussion Starter #1 (Edited)
I have a hydronic heater (Webasto Thermo Top C or TTC) factory installed under my van which helps speed up engine coolant on cold days, it automatically kicks in under 10C with the engine on.

I recently upgraded this heater with a kit to a "Parking Heater", which allows you to start up the TTC heater with a control panel without the engine on. Great to heat up the cabin from the vents and pre-heat the engine block in the winter.
* The upgrade comes in two versions, for climatic and for climatronic, I have the manual climatic version.

Now I wanted the option to isolate a smaller coolant circuit, just for the heat exchangers, by-passing the engine block, but still with the option to go back and include engine pre-heating. Attached the coolant diagram for the T5.1

Doing some searching I found another additional upgrade kit, the "Comfort Island Based Circuit" that can be installed afterwards the "Parking Heater" upgrade.
Cool, BUT, the documents say: climatronic only + cabin heating only

I ordered the kit anyway and now studying...

Parking Heater upgrade

Comfort Island Based Circuit upgrade

What I understand from the diagram is that 2 relays control the working of the 3-way solenoid valve [4], which flows the coolant through the engine block at 0V (A->C) or excludes the engine block (bypass) when energized at 12V (A->B)

* The (+) to the 3-way valve is made or broken by the K1 relay, the input is the working of the TTC heater.
When the heater is OFF, the (+) is broken at 87a
When the heater is ON, the K1 relay is energized and the (+) is made at 87
* The (-) to the 3-way valve is made or broken by the K2 relay, the input is the lighting switch.
When the lights are OFF, the (-) is made at 87a
When the lights are ON, the K2 relay is energized and the (-) is broken at 87

Now 3 questions....

1. I guess when the lights are OFF, the IGN should be OFF, which should mean the engine is OFF right? I think it is very important that with the engine ON I ABSOLUTELY want to make sure the coolant flows trough the engine block.
[*]What if my lightbulb(s) blow? Are there situations where I would turn the engine on and the coolant would not flow through the engine block? Could I make this better?

2. How about if I wanted to program my Webasto controller with the timer function, if I wanted to pre-heat the engine in the morning before driving of to work.
Would a simple switch - set to break so OFF - in wire [8], between the 18 pin connector of the lighting switch [St B] and the 86K2 pin, be enough? Or anywhere else, in the negatives wires maybe [6],[5],[4],[3]?
If I would use the same method but I wanted to quickly heat just the interior before driving off, I would just need to set that switch to ON and open the fan controls a bit the night before, right?

3. I am not sure about the second pin (from left) on the the 4-pin of digital timer [VWU]
The wire is black in my climatic "Parking Heater" upgrade and installed as such.
Remember that the "Comfort Island Based Circuit" upgrade should be for climatronic

The docs say: insert additional violet wire with micrometer into free socket of connector [VWU].
No clue as to what the micrometer with the violet wire would be. When looking at the climatronic electric diagram for the "Parking Heater" upgrade, indeed I see the second (black) pin is free! (the upgrade for climatronic does not have a relay, just a fuse)
So, should I just cut in my climatic black wire and splice in the green/white wire to 86K1? When the heater is ON, current will energize the K1 relay right? Just like it should energize the K3 relay from the "Parking Heater" upgrade, I hope??
Do I need a bigger diameter than 0.5mm before the splice?

Premium Member
174 Posts
Discussion Starter #2 (Edited)
I am going to finish the "Parking Heater" upgrade this weekend.
More research on the "Comfort Island Based Circuit" upgrade.

Question 1:
Turn light switch half way between off and side lights and pull. The light switch will come out and you will see the loom connected to it. In there are two thick black/yellow wires.

This is a circuit known as X relief. Comes live with ignition but drops out during engine cranking. This will prevent power being drawn from the leisure battery for starting.

Question 2:
I guess I need to insert that manual switch in the (+) blue wire [7] from the K1 relay to the 3-way valve, right?

Question 3:
I guess when the heater comes on it provides power to the K3 relais, just like it should provide power to the K1 relais?

>>> Please anybody has some thoughts or correct me if I am wrong?
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