Self Study Programme 280 Phaeton auxiliary heater top c and top z

The Phaeton
Auxiliary heater Thermo TOP C and
supplementary heater Thermo TOP Z

Design and function

Self-study programme 280

Service.

NEW Important

Note

This self-study programme explains the design and

function of new developments.

The contents will not be updated.

Please refer to the relevant service literature for

current inspection, adjustment and repair instructions.

The use of heater units that work
independently of the engine is continually rising.
They are offered as an accessory for retrofit or as
an optional extra by the manufacturer.

The petrol engine Phaeton features an auxiliary
heater as an optional extra that heats the interior
when the engine is not running.

For diesel engines, the Phaeton is fitted as
standard with a supplementary heater that
boosts coolant heating when the engine is
running.

In this way, the operating temperature of the
engine is reached faster and is maintained
throughout operation at an equal level.

This self-study programme provides you with an
overview of the auxiliary heater and the
supplementary heater installed in the Phaeton.

S280_053

Contents

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Coolant circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

Function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

Operating stages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

Deactivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

Network . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

Functional diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

Service . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

Explanation of highlighted terms

Test yourself . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

Introduction

The auxiliary heater

The auxiliary heater is a wise choice as an
accessory. The heater and ventilation function
provides a comfortable environment in the
interior, which is available as soon as you climb
into the vehicle.

Frosted or steamed up windows inhibit all-round
view. Therefore, they are a considerable risk in
traffic situations.

Heavy winter clothing, when worn in the vehicle,
results in loose seat belts as they are no longer
comfortably taut against the body. The optimal
efficiency of the seat belt is markedly impaired.
A further disadvantage is that unsuitable
clothing restricts freedom and thereby also the
ability to react quickly to given situations.

By heating up the interior before the journey is
started, the windows are cleared.
Good all-round view is guaranteed.

Less restrictive clothing in a preheated vehicle
increases the efficiency of seat belt protection
and reaction time of the wearer.

Further, use of an auxiliary heater is financially
viable. In many regions, the temperature on
100 days of the year is less than +5 °C, which
equals a third of a year of operation.

S280_013

S280_012

The supplementary heater

The diesel engines in the Phaeton feature
a heater that works to boost heat.

When the engine is started, the coolant is heated
additionally by the supplementary heater.
This helps diesel engines to make use of their
good efficiency and reach their operating
temperature in a short space of time.

The heat generated from the combustion process
is an unavoidable side-effect. The energy stored
within is converted partly into heat instead of
power.
This has the effect of reducing the degree of
efficiency.

Direct injection diesel engines reach a high level
of efficiency thanks to their optimised combustion
process. The use of a supplementary heater
supports the high level of efficiency in the engine
by heating of the coolant. In addition,
the passenger compartment is heated
comfortably.

Activation

Operation

The auxiliary heater can be operated in a number of different ways:

●

Immediate start is carried out via the front information display and operating unit, in the sub-menu of
the air conditioning system.

●

Programming a fixed start time is done via a timer in the same sub-menu.

●

Additionally, the auxiliary heater can be started using a remote control.

Immediate start

By pressing the auxiliary heater function button, the sub-menu can be accessed
for auxiliary heater control.
The heater button allows manual activation and deactivation of the auxiliary heater.

S280_008

Heater button for immediate start

22°C

92.8 MHz TP

A/C

Other functions/Auxiliary heater

Timer (duration:10 min)

Monday

06:20

Heater

Back

Duration

Day

Departure
time

Sel-
ection

Front information display and operating unit

S280_021

When the auxiliary heater is activated at temperatures above +22 °C, auxiliary ventilation is
activated automatically.

Display: Set duration

Timer preselection

The start time for the heater can be programmed in the sub-menu. To do this, the weekday,
the start time and the desired duration should be entered using the operating elements.

When the weekday and time have been reached, auxiliary heater operation will begin. In addition, the
weekday will jump automatically to the next day.

S280_061

Display:
Weekday,
time

22°C

92.8 MHz

A/C

Other functions/Auxiliary heater

Timer (duration:10 min)

Monday

06:20

Heater

Back

Duration

Day

Departure

time

Sel-

ection

Display: Timer preselection

Tuesday

08:50

22°C

92.8 MHz

A/C

..../Auxiliary heater/Heating duration

Back

Confir-

mation

15 min

Display:
Duration

Remote start

The auxiliary heater features an additional
remote control, which is not integrated in the
vehicle key.

With this remote control, the auxiliary heater is
switched on and off remotely.

The on button serves to start the heater and the
off button is used to switch it off.

For power supply of the remote control, a battery
is necessary.

The range of the remote control in open areas is
approx. 600 m.

The control lamp of the remote control lights up
green when the auxiliary heater is switched on,
and red when it is switched off.

Operation

S280_023

On button

Off button

Remote control

Control lamp

S280_066

Opening for battery replacement

The signal is sent to the auxiliary heater control
unit (J255) by pulse width modulated
transmission along a special data lead.

The radio signal from the remote control is
pikked up by an aerial, which is installed in the
upper area of the rear window, and transmitted
to a receiver located beneath the rear shelf.

The remote control must be coded to the radio receiver. A maximum of two remote controls can
be coded. The work procedure necessary is described in the electronic service information
system (ELSA).

Remote control

Aerial

Radio receiver

Auxiliary heater control unit

S280_019

Overview of associated components

Fitting locations

The components necessary for operation of the
auxiliary heater or the supplementary heater are
installed in the vehicle decentrally.

Overview

Auxiliary/supplementary heater
with control unit,
front left beneath wing

Pump valve unit,
front right in vicinity of plenum
chamber

Overview of fitting locations

Metering pump,
above rear axle,
left of centre

Radio receiver,
beneath rear shelf

S280_017

Aerial for remote start,
beneath rear window upper
trim

Coolant shutoff valve,
on left in engine compartment

The components

The auxiliary heater and the supplementary
heater consist of:

- recirculating pump V55,
- combustion air blower V6,
- control unit J255,
- burner housing,
- combustion chamber with flame pipe and

glow plug Q9 (with flame monitor) in burner
housing,

- coolant jacket.

Additional components are:

- metering pump V54 and
- coolant shutoff valve N279.

Construction

S280_002

Recirculating pump

Burner housing

Coolant jacket

Combustion air blower V6

Combustion chamber in
burner housing

Thermo Top Z/C (heater)

Control unit

The recirculating pump V55

When the engine is switched off, coolant is
circulated by a recirculating pump. This is
actuated electrically by auxiliary heater control
unit J255.

Actuation

Actuation is by the auxiliary heater control unit.

S280_057

S280_044

S280_007

Recirculating pump

Cross section

Iron core

Permanent magnet

Coil

Pump rotor

The combustion air blower V6

The air required for combustion is drawn in via
an air intake pipe with silencer by the
combustion air blower, then via the air channel
to the fuel evaporator (fleece) and further to the
combustion chamber.

Construction

S280_003

Silencer

Combustion air blower

Main view

Silencer and filter element

S280_058

Air intake

Actuation

The combustion air blower is supplied with
voltage direct from the control unit via a two pin
connector.

S280_047

Blower rotor with vanes

Blower motor

S280_059

S280_055

Housing

Air intake

Construction

Control unit

S280_004

Connector strip

The auxiliary heater control unit J255

Main view

As primary control unit, the control unit guarantees the functional sequence and monitor heater
operation.

Connection to the vehicle onboard electrical system is via a connector strip.

The supplementary heater and the auxiliary heater differ in control unit codes and connection to the
coolant circuit. In addition, the auxiliary heater has a remote start function and a coolant shutoff valve.

Temperature monitoring

Coolant temperature is monitored in the heater
and heater operation is regulated via the
temperature sender G241. At coolant
temperatures above 125 °C, the heater is
shut off and locked.

To unlock, follow the instructions on the diagno-
sis, testing and information system VAS 5051 and
the electronic service information system (ELSA).

S280_054

Control unit opened

S280_065

Temperature sender

Glow plug with flame monitor Q9

Power supply

Combustion air blower V6

Recirculating pump V55

Connector to onboard
electrical system

S280_035

The burner housing

Located on the burner housing are:

- the coolant outlet,
- the exhaust pipe,
- the coolant inlet and
- the combustion chamber.

Construction

Coolant inlet

Coolant outlet

S280_027

Further, the burner housing houses the combustion chamber and forms a unit with the coolant
jacket and the control unit.

Combustion
chamber

Burner housing

Exhaust pipe

Formation of the fuel-air mixture takes place in
the combustion chamber. This mixture is then
burnt in the flame pipe.

The glow plug with flame monitor can be found
in the combustion chamber. This ignites the
fuel-air mixture initially. During the heating
stage, the glowing walls of the combustion
chamber ignite the fuel-air mixture.

The glow plug is designed as an electrical
resistor and features a flame monitor. It monitors
the temperature of the flame during the whole
phase of heating.

Glow plug with flame monitor

S280_005

Combustion air inlet

Combustion air inlet
into
fuel evaporator

Fuel intake

Flame pipe

The combustion chamber with flame
pipe and heater glow plug Q9 (with flame monitor)

Combustion air inlet

Flame pipe

Combustion chamber

Combustion chamber cross section

S280_056

The coolant jacket.

Construction

Coolant jacket

S280_004

Coolant inlet

Coolant outlet

Space for coolant
(transfer of heat)

Main view

Coolant jacket cross section

Space for combustion chamber

S280_060

The heat generated from combustion is conveyed to the coolant via the coolant jacket.

Coolant enters the housing via the coolant inlet of the coolant jacket (heat transmitter). The necessary
heat is then drawn for heating. Coolant leaves the housing via the coolant outlet.

The exhaust system

S280_025

Silencer

Exhaust pipe

The heater features its own exhaust system, which consists of an exhaust pipe and silencer. The exhaust
system channels the exhaust gas generated from heater combustion to the outside independently of the
vehicle exhaust system.
In order to guarantee safe operation of the heater, the prescribed length of the exhaust system should
not be altered.
The length is set to balance the combustion vibrations of the heater.

The metering pump V54

Supply of fuel from the fuel tank of the vehicle to
the heater is by metering pump. The pump is
designed as a combined supply, metering and
shutoff system. This means that fuel is metered
during operation and fuel supply is blocked
when the heater is switched off.

Fitting location

The metering pump can be found above the rear
axle. To remove the pump, the rear axle has to be
lowered. In order to ensure correct ventilation of
the pump, the prescribed fitting location must not
be changed.

Actuation

The metering pump is pulse-actuated via the
control unit based on the required heater output.

Construction

S280_014

S280_063

S280_046

Functional description

The metering pump is of the plunger type, in
which the armature is attached permanently to
the pump plunger.

Supply of fuel

The metering pump is filled with fuel when there
is no voltage.
When the coil is energised, the armature pushes
the pump plunger against the spring.
The pump plunger lifts up the ball valve and
delivers fuel from the pump chamber. At the
same time, the supply hole to the pump chamber
is closed.

Fuel suction

During this period, fuel flows in the armature
chamber. When the coil is not energised, spring
pressure forces the armature and the pump
plunger back.
The resulting vacuum draws fuel into the pump
chamber via the opened inlet holes.

This kind of operation allows a high level of
metering accuracy, high durability and low noise
generation.

S280_067

Coil

Ball valve

Armature

Pump plunger

Spring

Inlet hole

Pump chamber

Armature

chamber

S280_062

Armature

Pump plunger

Pump chamber

Inlet hole

An animated view of the function can be found on the internet at
"www.thomas-magnete.com"

Only the auxiliary heater features a coolant
shutoff valve. When the auxiliary heater is in
operation, engine coolant circulation is
separated from the heat exchangers to the
interior.
Separation is via the coolant shutoff valve.

Fitting location

The coolant shutoff valve can be found on the
left in the engine compartment.

Actuation

The auxiliary heater control unit actuates the
valve directly.

Construction

To engine

From pump valve unit

To heater

S280_016

Plug

S280_064

Coolant shutoff valve N279

S280_048

Normal operation

When there is no power, the coolant shutoff
valve connects the coolant circuit between the
pump valve unit and engine circuit.

Heater operation

The shutoff valve is actuated and the pump valve
unit is connected with the auxiliary heater.
In this way, the interior of the vehicle is
preheated and not the engine.

To engine

From pump valve unit

Plug

Coil

Valve plunger

To engine

From pump valve unit

To heater

Plug

Coil

Valve plunger

S280_050

S280_051

To heater

Coolant circuit

Connection of auxiliary heater in coolant circuit of W12 engine

If the auxiliary heater is started when the engine is switched off, the coolant shutoff valve closes.
The recirculating pump pumps coolant through the coolant jacket in the auxiliary heater to the pump
valve unit, then through the heat exchanger inside the vehicle and back to the auxiliary heater.
The vehicle interior is heated.

Gearbox oil cooler

Engine oil cooler

Alternator C

Cylinder block

Coolant circuit

Coolant shutoff valve N279

Function

When voltage is applied to the shutoff valve, coolant can flow from the pump valve unit to the heater.
When there is no voltage at the shutoff valve, coolant can flow from the pump valve unit to the engine.

Recirculating pump
V55

Auxiliary heater

Pump valve unit

Left heat exchanger

Right heat exchanger

Expansion tank

Air reservoir

Continued coolant circulation pump V51

Thermostat

Radiator

The pump valve unit is part of the
vehicle heater and is described in
SSP 271.

S280_015

Coolant circuit

Connection of auxiliary heater in coolant circuit of V10 TDI engine

On the supplementary heater there is no coolant shutoff valve. The heater is permanently connected to
the engine coolant circuit.

Coolant circuit

Low temperature cooler for
alternator and fuel cooling

Radiator

Fuel cooling pump V166

Continued coolant circulation pump
V51

Check valve

Expansion tank

Right heat exchanger

Left heat exchanger

Pump valve unit

Supplementary heater

S280_052

Recirculating pump
V55

Air supply

The air required for combustion is drawn via the
combustion air intake from the combustion air
blower and passed through the combustion air
channel to the combustion chamber.

Function

Combustion air blower V6

Coolant outlet

Combustion air inlet

Fuel channel

Coolant inlet

Metering pump V54

Combustion air channel

Heater glow plug Q9
(with flame monitor)

Fuel evaporator

Exhaust pipe

Recirculating pump V55

The fuel supply

Fuel is supplied through the fuel channel. In the
fuel evaporator (fleece), fuel is mixed with the
combustion air, forming a combustible fuel-air
mixture.

The glow plug with flame monitor ignites the
mixture in the combustion chamber at the start.

Once operation has begun, ignition occurs at the
flame front in the flame pipe.

During operation of the heater, the glow plug Q9
is supplied with only a small amount of energy
from the control unit.
The electrical resistance of the glow plug can
thus be used as a flame monitor.

The coolant

Coolant enters through the coolant inlet in the
coolant jacket. Here, it is heated. The heated
coolant flows out the coolant outlet into the
coolant circuit.

S280_010

Coolant jacket

Flame pipe

Combustion chamber
in burner housing

The auxiliary heater

Start phase

The auxiliary heater is started either:

- immediately,
- via the timer or
- using the remote control.

The combustion air blower and the recirculating
pump are actuated.
The glow plug starts to glow and the combustion
air blower pumps air into the burner insert.
After about 30 seconds, the metering pump
starts to deliver fuel and the combustion air
blower is switched off for about 5 seconds until
a rich mixture has built up.

The output of the combustion air blower is
increased in stages to full load and the fuel-air
mixture is delivered to the combustion chamber.
Combustion begins.

If no flame is formed or the flame dies, restart is
initiated automatically. After a total of
90 seconds of fuel delivery without flame
formation, the system is switched off until the
ignition is switched on again (terminal 15).

Metering pump TL

Operating stages

Glow plug

Recirculating pump

Combustion air blower TL

Combustion air blower VL

Fresh air blower

Metering pump VL

Flame monitor interrogation

Temperature in °C

Time in seconds

Sta

com

stio

Ful

l l

oad oper

ion

Fre

r blower

load

Ful

l load

rt l

Sta

rt o

f ru

End

run-

S280_036

low

Heating phase/regulated phase

When the coolant reaches a temperature of
87 °C, the heater is switched from full load to
part load. This reduces the combustion air
blower output and the metering pump delivers
less fuel. If the coolant temperature drops to
approx. 83 °C, full load is activated again.

At a coolant temperature of approx. 89 °C,
heating is interrupted. When the coolant
temperature drops to approx. 85 °C, heating is
initiated once again.

Temperature in °C

S280_037

Sta

t o

f co

stio

ll l

oad

oper

ion

h ai

r blow

load

Ful

l l

oad

uto

rt l

t o

f ru

d of

Metering pump TL

Glow plug

Recirculating pump

Combustion air blower TL

Combustion air blower VL

Fresh air blower

Metering pump VL

Flame monitor interrogation

Run-on phase

The auxiliary heater is deactivated by:

- switching off the engine,
- switching off the auxiliary heater or
- expiration of the automatic heating duration

(max. 60 minutes).

The metering pump is switched off, combustion
stops, the combustion air blower and the
recirculating pump run-on to cool down and are
then switched off automatically.

Run-on time depends on the type of heater and
can be between 100 and 175 seconds.

The run-on time for petrol-driven heaters is:

●

168 seconds when switched off from full load

●

157 seconds when switched off from part load

The run-on time for diesel-driven heaters is:

●

175 seconds when switched off from full load

●

100 seconds when switched off from part load

There may be slight deviations in the given
figures depending on the development of the
software.

Operating phases

Temperature in °C

Time in seconds

100 - 175

S280_038

Metering pump TL

Glow plug

Recirculating pump

Combustion air blower TL

Combustion air blower VL

Fresh air blower

Metering pump VL

Flame monitor interrogation

t of

com

sti

load oper

Fre

rt l

Ful

l l

oad

load

Sta

End of

The supplementary heater
(diesel engines)

Start phase

When the engine is started, the heater is made
ready.
When the coolant temperature is below 60 °C,
ambient temperature is below + 5 °C and the
control unit has received an engine speed signal,
start is initiated.

Heating phase

If the coolant reaches 78 °C, operation is
interrupted. When the coolant temperature
reaches 76 °C, full load operation is switched to
part load. The transition from part load to full
load comes at 70 °C and to part load at 65 °C.

Run-on phase

When the engine is switched off, the
supplementary heater is stopped.
Combustion is stopped and run-on begins.

The supplementary heater run-on time is:

●

175 seconds when switched off from full-load

●

100 seconds when switched off from part-load

There may be slight deviations in the given
figures depending on the software version.

Temperature in °C

Time in seconds

S280_020

Sta

t o

f co

stio

ll l

oad

oper

ion

h ai

r blow

load

Ful

l l

oad

Shut

off

rt l

t of

d of

Metering pump TL

Glow plug

Recirculating pump

Combustion air blower TL

Combustion air blower VL

Fresh air blower

Metering pump VL

Flame monitor interrogation

100 - 175

Deactivation

The auxiliary heater and the supplementary
heater are switched off for reasons of safety
under certain conditions.

Vehicle-specific deactivation

The auxiliary heater is switched off when:

- the tank flap is opened,
- the fuel level is low,
- the onboard electrical system is placed under

heavy load by the onboard electrical system
control unit,

- an airbag is triggered by an accident
- heater output is sufficient during normal

driving.

Temperature related deactivation

If the coolant temperature rises above 105 °C
during heater operation, fuel supply is
interrupted.

In this instance, the heater will run-on for
approx. 120 seconds. If there is a fault in the
combustion air blower, there will be no run-on.

S280_028

Deactivation conditions

S280_024

Heater operation

Deactivation

Deactivation due to excessive or insufficient
voltage

In addition to monitoring of the onboard
electrical system voltage by the onboard
electrical system control unit, the auxiliary heater
control unit also deactivates the heater if
excessive or insufficient voltage is detected.

Fixed deactivation due to insufficient voltage

If the battery voltage drops to below 9.5 volts for
longer than 6 seconds, the heater is deactivated
with a run-on time of 120 seconds.

Deactivation due to excessive voltage

If the battery voltage exceeds 15.5 volts for more
than 60 seconds, the auxiliary heater is
deactivated.

S280_029

Heater operation

Deactivation

The auxiliary heater control unit is connected
with the other control units in the vehicle via the
infotainment CAN data bus and the diagnosis
data bus interface in the dash panel. All the
necessary information can be exchanged with
other control units via this data network.

Networking

Control unit for front informa-
tion display and operating
unit

Communication via CAN data bus

Roof electronics control unit
J528

Climatronic/air conditioning control unit
J301

Onboard electrical supply control unit J519

Entry and start authorisation control unit J518

Door control unit, driver side
J386

Climatronic operating and control unit
E265

Auxiliary heater control unit
J255

Drive train CAN data bus

Convenience CAN data bus

Infotainment CAN data bus

S280_034

Data bus diagnosis interface

Control unit for front information
display and control unit
J523

Data bus diagnosis interface
J533
in dash panel

The data bus messages

A) Function

B) Message

Auxiliary heater messages received from remote
commands and from modes of operation

Activation via remote control
Activation of blower
Activation of control LED

Commands and information to auxiliary heater control
unit

Activation of auxiliary heater
Tank warning on
Convenience CAN data bus messages

Terminal information

Ignition on

Auxiliary heater operation

Operating commands
e.g. auxiliary ventilation
e.g. immediate start

Auxiliary heater operation

Auxiliary heater operating mode
Heating duration

Programming of auxiliary heater

Start time

Actuation of auxiliary heater

Auxiliary heater operating mode

Auxiliary heater duration information

Auxiliary heater duration

Heater deactivation

Tank flap opened

Heater deactivation

Onboard electrical system critical battery level

Heater deactivation

Crash impact signal

Status information

Engine speed
Ambient temperature
Engine type

Networking

C) Sender

D) Receiver

Auxiliary heater control unit

Control unit with display unit in dash panel insert
Climatronic/air conditioning control unit
Roof electronics control unit
Entry and start authorisation control unit
Onboard electrical supply control unit
Control unit for front information display and
operating unit
Climatronic/air conditioning
operating and display unit