Audi Q7 2007 Repair Manual page 95

Note
Since resistances smaller than 10 ohm cannot be measured
♦
with sufficient precision using workshop tools, a short circuit in
the Auxiliary Heater Heating Element - Z35- cannot be deter‐
mined.
The current that flows via the Auxiliary Heater Heating Ele‐
♦
ment - Z35- is routed to the vehicle body via the ground point
-C- and the instrument panel crossmember. If there is a con‐
tact resistance between the instrument panel crossmember
and the body, the function of the Auxiliary Heater Heating El‐
ement - Z35- will be compromised. Refer to Wiring diagrams,
Troubleshooting and Component locations.
The resistance elements are activated via the relevant engine
♦
control module in three stages (example of an auxiliary heater
heating element -Z35- with 1200 W: stage 1, approximately
400 W via contact "1" inside the connector -B-; stage 2, ap‐
proximately 800 W via the contact "2" inside the connector
-B-; and stage 3, approximately 1200 W via both contacts in‐
side the connector -B-).
When the temperature of the Auxiliary Heater Heating Ele‐
♦
ment - Z35- reaches 20° C (68° F) , the resistance between
the contact "1" inside the connector -B- and the ground point
-C- will be approximately 0.6 ohms. Between the contact "2"
inside the connector -B- and the ground point -C- it will be ap‐
proximately 0.3 ohms. If the heating element was activated,
the electrical resistance increases (if the component temper‐
ature reaches approximately 60° C (140° F), it is already
greater than 2 or 2 ohms).
The resistance elements are activated via the engine control
♦
module and the different relays (for example, the Low Heat
Output Relay - J359- and the High Heat Output Relay - J360- )
in three stages (stage "1" approximately 400 W via the -J359- ,
stage "2" approximately 800 W via the -J360- and stage "3"
approximately 1200 W via both relays). Depending on the ver‐
sion, the activation of stage "2" can also occur via two separate
relays. Refer to Wiring diagrams, Troubleshooting and Com‐
ponent locations.
The Auxiliary Heater Heating Element - Z35- is designed so
♦
that, when switched on, no current greater than 40 A /45 A
flows via the contact "1" inside the connector -B- and no cur‐
rent great than 80 A/90 A flows via the contact "2" inside the
connector -B- (the resistance increases and the current de‐
creases immediately after the switching on).
The Auxiliary Heater Heating Element - Z35- is comprised of
♦
several layers of resistance elements that collectively achieve
a heating output of approximately 1200 W/1500 W (when ac‐
tivating both stages "1" and "2" at the same time). These
resistance elements have a positive temperature coefficient
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permitted unless authorised by AUDI AG. AUDI AG does not guarantee or accept any liability
(their resistance increases with the temperature and the cur‐
with respect to the correctness of information in this document. Copyright by AUDI AG.
rent consumption decreases), so that the nominal output is
achieved only at a low component temperature.
Conditions for Activating the Auxiliary Heater Heating Element -
Z35-
The following conditions must be met in order for the engine con‐
trol module to activate the Auxiliary Heater Heating Element -
Z35- . Use the Vehicle Diagnostic Tester via the "Guided Fault
Finding" function:
♦ The engine speed is greater than 500 RPM
♦ The ambient temperature is below 10° C (50° F).
Heating, Ventilation and Air Conditioning - Edition 04.2013
8. Components Actuated by A/C System, Electrical Test
Audi Q7 2007 ➤
89