GF83.70-D-0009H PTC Heater Booster, Function

GF83.70-D-0009H PTC Heater Booster, Function

- with CODE (HH2) Electric warm air auxiliary heater

Due to the use of engine OM642 and engine OM646, the waste heat produced by the engines for vehicle heating is decreasing more and more. Therefore, to meet the legal requirements (deicing of windshield) and to ensure adequate heating comfort, a "PTC heater booster" with a heat output of 1.8 kW is integrated in the vehicle heating system. The PTC heater booster system consists of the following two components:
- Electric PTC heater booster (N33/4)
- PTC heater booster

The Electric PTC heater booster regulates the PTC heater booster cyclically via a pulse width modulation (PWM) signal from 0 to 100 % (frequency per stage f = 50 Hz). In the process, the charge signal of the alternator (G2/7) (IF signal) is constantly being monitored. The PTC heater booster is regulated depending on the IF signal up to 95 %.

The electric PTC heater booster is connected to the Controller Area Network bus class B (interior) (CAN-B) and uses it to read in the following status and the following messages:
- Status circuit 61
- "LL_STBL (idle is stable)"
- "T_MOT (engine coolant temperature)"
- "T_AUSSEN_K (instrument cluster filtered outside temperature (A1) "

The specification of the PTC heater booster's heat output depends on the following two variants:
- Heater, except CODE (HH9) Regulated air conditioning (Tempmatic)
- Tempmatic (TM), with code (HH9) Regulated air conditioning (Tempmatic)

Specification of heat output with heater variant, except code (HH9) Regulated air conditioning (Tempmatic)
Function requirements:
- Terminal 61 ON
- Stable idle mode
- Coolant temperature < 80 °C
- outside temperature < 13 °C

With the heater variant, the electric PTC heater booster independently regulates its output depending on the coolant temperature and on the outside temperature according to a stored performance map.
The electric PTC heater booster receives the coolant temperature information from the coolant temperature sensor (B11/4) and the outside temperature information from the outside air temperature sensor (B14) via CAN-B.

Specification of heat output with TM variant, with code (HH9) Regulated air conditioning (Tempmatic)
Function requirements:
- Terminal 61 ON
- Stable idle mode
- Coolant temperature < 80 °C
- outside temperature < 10 °C

With the Tempmatic variant, the electric PTC heater booster is regulated depending on the temperature set via the temperature selection switch (S98s14) integrated in the KLA control and operating unit (S98). The electric PTC heater booster reads in this specified value from the KLA control and operating unit via CAN-B. The electric PTC heater booster receives the coolant temperature information from the coolant temperature sensor and the outside temperature information from the outside air temperature sensor via CAN-B also. The KLA control and operating unit specifies a specified output value in the range of 0 to 100 % (10 % increments) for the electric PTC heater booster via CAN-B.

When the specified temperature in the vehicle interior set on the KLA control and operating unit has been reached, it is cut off in 10-% steps.

Shutoff requirements for immediately cutting off the PTC heater booster (shutoff time < 100 ms)
If a fault is detected at the outputs of the electric PTC heater booster, the affected outputs are shut off as quickly as possible. When there are no more errors present, the deactivated outputs are switched on again immediately with the currently valid cycle ratio (PWM signal).

Shutoff requirements for quickly cutting off the PTC heater booster (approx. 10 % per second)
If the electric PTC heater booster detects a faulty message, the PTC heater booster is switched off.

Shutoff requirements for directly switching off the PTC heater booster (approx. 100 % per second)
The electric PTC heater booster cuts off the PTC heater booster directly, if one of the following conditions is present:
- Circuit 61 OFF
- Idle is unstable
- "KOMP_NOTAUS (refrigerant compressor (A9) emergency off)"
- "KOMP_BAUS (switch refrigerant compressor off, acceleration)"

The message "KOMP_NOTAUS (refrigerant compressor emergency off)" and the message "KOMP_BAUS (switch refrigerant compressor off, acceleration)" are placed on the CAN-B via the EIS control unit (N73) by the CDI control unit (N3/20), with engine OM642, or by the CDI control unit (N3/21), with engine OM646.

Temperature shutoff of PTC heater booster
When the temperature of the electric PTC heater booster's printed circuit board is > 105 °C, the outputs are switched off.
Reactivation takes place after the temperature has dropped to < 85 °C and a waiting time of t = 30 s (after shout off) has elapsed.

Shutoff requirements for normal cutting-off of the PTC heater booster (approx. 4 % per second)
The electric PTC heater booster cuts off the PTC heater booster, if one of the following conditions is present:
- Coolant temperature > 80 °C
- Outside temperature > 13 °C with the heater variant , except code (HH9) Regulated air conditioning (Tempmatic)
- Outside temperature > 10 °C with the TM variant, with code (HH9) Regulated air conditioning (Tempmatic)

Undervoltage and overvoltage shutoff of the PTC heater booster
The electric PTC heater booster shuts off the PTC heater booster, when the following undervoltage or overvoltage values are present:
- Undervoltage
Switch-off threshold = U < 7 V
Switch-on threshold = U > 7.8 V

- Overvoltage
Switch-off threshold = U > 17 V
Switch-on threshold = U < 16.2 V