Auxiliary Cabin Heater: Testing and Inspection
Auxiliary Heater Heating Element (Z35), Testing
• Currently, certain gasoline engines (for example, vehicles that can use bioethanol "Flex Fuel Vehicle" from MY 10 and on high voltage vehicles) have an electric auxiliary heater. Refer to the Audi Sales Program. The air is supplied with heat energy after leaving the heater core if there is a request from the Climatronic Control module (J255).
• The air is supplied with heat energy via the auxiliary heater heating element after it has left the A/C heater core.
• Vehicles without an auxiliary heater heating element have a honey comb installed inside the A/C System in place of the auxiliary heater heating element (Z35). Refer to => [ Auxiliary Air Heater Heating Element (Z35)/Honey Comb ] Service and Repair.
• The respective engine control module activates the electrical auxiliary heater (the auxiliary heater heating element) (the control modules exchange information about this via the data bus system). Refer to the Vehicle diagnostic tester in "Guided Fault Finding".
• The activation of the electric auxiliary heater (the auxiliary heater heating element) occurs for vehicles with a gasoline engine from the Climatronic control module (J255) control head via the local Data bus (controlled using the same outlet and also using the fresh air blower control module (J126) ) on the auxiliary air heater control module (J604). The auxiliary air heater control module (J604) activates the low heat output relay (J359) and the high heat output relay (J360) and these send the electricity to the auxiliary heater heating element (Z35). Refer to the Vehicle diagnostic tester in "Guided Fault Finding".
• The request to turn on the electric auxiliary heater being sent to the respective engine control module / auxiliary air heater control module (J604) appears in the measured values block for the Climatronic control module. Refer to the Vehicle diagnostic tester in "Guided Fault Finding".
• The auxiliary air heater control module (J604) installed on vehicles with a certain gasoline engines is currently not Vehicle Diagnosis, Testing and Information System VAS 5051 in "Guided Fault Finding" diagnostic-capable. Refer to the Vehicle diagnostic tester in "Guided Fault Finding" to verify.
• The test for the activation of the auxiliary heater heating element is found in Guided Fault Finding for the A/C system. Refer to the Vehicle diagnostic tester in "Guided Fault Finding".
• In MY 2009, as a running change, a new version of the auxiliary heater heating element is being installed (the heating element is a bit more narrow); be sure to use the correct version and note the allocation. Refer to Electronic Parts Catalog (ETKA).
• From MY 2010, this vehicle has a Start/Stop System for specific engines as optional equipment. On vehicles with the Start/Stop System. the auxiliary heater heating element is switched off when the Stop function is active (to protect the battery (A) ). After the engine is started with the Start function, the auxiliary heater heating element is switched on again. Refer to the Vehicle diagnostic tester in "Guided Fault Finding".
• Check resistance value of auxiliary heater heating element using the Vehicle diagnostic tester in "Guided Fault Finding".
Auxiliary air heater heating element (Z35) design and functionality
• The auxiliary heater heating element is comprised of several layers of resistance elements - E - and - F -. These can achieve a heating output of approximately 1000 W via all 3 - A - through - C -. These resistance elements have a positive temperature coefficient (the resistance increases with the temperature and current pick and the heating output decrease).
• The resistance heating elements (- E - and - F -) are activated via the cables - A - through - C -; the current flows through the ground connection - D -.
• The auxiliary heater heating element is designed so that a current greater the 35 A can flow via the contacts - A - through - C - when switched on. Immediately after switching on, the resistance on the resistance heating elements - E - and - F - increases and the current goes down.
• To reach the maximum heating output of approximately 1000 W (3 x 333 W), the resistance heating elements temperature must be low and the generator (C) must deliver enough current.
• Wire - A - provides the voltage to the resistance heating elements - F - via the low heat output relay (J359).
• Wires - B - and - C - provide the voltage to the resistance heating elements - E - via the high heat output relay (J360).
• The resistance of the heating elements depends on the temperature; the resistance is approximately 0. 2 to 5 ohms (measured between the connections - A -, - B - and - C - (in the connector) and the ground connection - D -
• To measure the resistances and to check the activation of the auxiliary heater heating element disconnect the connector on the A/C => [ Auxiliary Air Heater Heating Element (Z35)/Honey Comb ] Service and Repair
• Since resistances smaller than 10 ohms cannot be measured with sufficient exactness using workshop tools, a short circuit in the auxiliary heater heating element cannot be determined.
• Activate the preheating coolant, low heat output relay (J359) and the preheating coolant, high heat output relay (J360) in order to check the function, for example, "control diagnosis" of each engine control module and when doing so, measure the voltages between the contacts in the counter terminal to the terminal on the auxiliary heater heating element and the ground using the Vehicle diagnostic tester in "Guided Fault Finding".
• The engine control module / auxiliary air heater control module (J604) activates the auxiliary heater heating element in 3 stages. Contacts - A -, - B - and - C - are supplied with voltage as follows. Refer to the wiring diagram.
- For stage "1" the voltage from the Preheating Coolant, Low Heat Output Relay (J359) is switched to the contact - A -
- For stage "2" , stage "1" is switched off and the voltage is switched via the Preheating Coolant, High Heat Output Relay (J360) to contacts - B - and - C -.
- For stage 3 "3", stage "2" and stage "1" are switched on. Check using the Vehicle diagnostic tester in "Guided Fault Finding".
• The control module constantly monitors the generator (C) load. The next stage is selected if the load remains under a certain limit. If the load exceeds a specified limit, then the stage is switched down.
Switch-on criteria for electric auxiliary heater activation
• The switch on conditions in the Climatronic control module must be met so that the request can be sent to the respective engine control module.
- The Climatronic control module sends a request to switch on the auxiliary heater to the engine control module as long as the following requirements are fulfilled:
• Engine is running for a minimum of 8 seconds and engine speed is greater than 500 RPM.
• Engine temperature is less than 75 °C (167 °F).
• The calculated outside air temperature is lower than 8 °C (46 °F).
• Vehicle voltage supply is greater than 12.2 volts and no request that forbids the switch-on is sent by Vehicle Electrical System Control Module (J519).
• No DTCs are stored in Climatronic control module.
• No DTC is stored in Engine Control Module (ECM) and Generator (GEN) (C) load is less than 30 to 77% (depending on engine speed).
• Based on the setting and the measured temperatures, the Climatronic control module has calculated that additional heat output is necessary to reach the intended passenger compartment temperature.
• The Climatronic control module has calculated that more than 90% of the air will be guided through the heater core.
• The engine control module / auxiliary air heater control module (J604) activates the auxiliary heater heating element (3-stage) via both auxiliary heating relays ( low heat output relay (J359) and preheating coolant, high heat output relay (J360) ), so that the load on the generator (C) does not exceed 95%. Refer to the Vehicle diagnostic tester in "Guided Fault Finding" for the A/C control module and to. Thus the next stage is switched on only in the event generator load is less than 30 to 77%, depending on engine speed.
Switch-off criteria for electric auxiliary heater activation
• The activation is switched off as soon as a switch on requirement is no longer filled in the Climatronic control module or respective engine control module or one of the switch off criteria has been detected.
- The Climatronic control module switches off the request to switch on the electrical auxiliary heater.
• When one of the switch-on requirements is no longer met.
• The calculated outside air temperature is higher than 11 °C (52 °F).
• Generator load is greater than 95%.
• The Climatronic control module has calculated that less than 60% of the air will be guided through the heater core (position of temperature doors)