Electrical Testing

Electrical Testing

Electrical tests (to be performed on A/C Control Head -E87-) overview

Test Step 1 - 3:

Test Step 4 - 7:

Test step 1 - Voltage supply, Ground (GND) connection and illumination for A/C control head -E87-

Test Step 1.1 - 1.2:

Test Step 1.3 - 1.4:

Test Step 1.5:

Test Step 1.7:

Test Step 1.8 - 1.9:

Test step 2 (Temperature sensors/senders)

Test Step 2.1 - 2.3:

Test Step 2.4 - 2.5:

Outside temperature dependent resistance values of temperature sensors/senders in Kohms (Kilo-Ohm)

Test step 3 - Fresh air blower -V2- and Control module for fresh air blower -J126-

Test Step 3.1 - 3.2:

Test Step 3.3 - 3.4:

Test step 4 - Air conditioner positioning motors with potentiometers

Test Step 4.1 - 4.2:

NOTE:
- The resistance value of potentiometer in the positioning motors (Specification: 3.6 k Ohms to 5.7 k Ohms between terminal 1 and 3) can only be measured directly at the motor (connected in parallel).
- The resistance of the potentiometers in the positioning motors (between terminals 1 and 2 and between terminals 3 and 2) depends on the position of the positioning motor, and must always be measured with the positioning motors installed. The maximum specified value would not be obtained in test step 4.1 and 4.2. To obtain the maximum specified value, all the connectors on the other positioning motors would have to be disconnected (motors are connected in parallel).
- If the A/C Control Head -E87- detects the malfunction "Potentiometer short circuit to Ground (GND)" or "Open/short circuit to B+", check all the potentiometer (one in each of the 5 positioning motors) and the wiring.
- If the read out for the DTC memory shows that more than one of the positioning motors is malfunctioning but no DTCs are identified in the test step 4, test for short circuits in wiring to and between the individual positioning motors (e.g. between -V70- and -V71-).

Test Step 4.3 - 4.4:

Test Step 4.5 - 4.7:

Test step 5 - A/C Pressure Switch -F129-, output for "A/C compressor cut-in" and signal indicating "engine temperature too high"

Test Step 5.1:

Check for loose terminals in wiring connection to A/C pressure switch -F129- according to wiring diagram.
- Check activation of Coolant fan -V7- step 1 (See output Diagnostic Test Mode). [1][2]Output Diagnostic Test Mode (DTM) (Function 03)
- A/C pressure switch -F129- (switch between terminals 3 and 4, check activation of Coolant fan - V7- step 2) .

If no malfunctions can be determined, check pressures in refrigerant circuit.

Test Step 5.2:

- Coding (allocation) of ignition key is transmitted to the A/C control head -E87- from the instrument cluster along with the coolant temperature and the signal "engine temperature too high" when ignition is switched on for vehicles from m.y. 2000 (data message). Coding of key can only be processed by A/C control heads -E87- with part number 8D0 820 043 with index "H", "J", "K" or "L" as well from index "T" and with index "AE", "AF", "AG" and "AH". No information can be transmitted if the coolant temperature is too high.
- When ignition is switched on, A/C control head -E87- begins with the setting that was valid when the ignition was last switched off with this key (temperature, air distribution, fresh air blower RPM).
- The instrument cluster can only be transmit the coding of the ignition key on vehicles equipped with immobilizer.
- The signal from instrument cluster (data message) cannot be checked with workshop tools.

Test Step 5.3:

Test Step 5.4:

NOTE: Ground is at, for example, connector -D-, socket 14 and 15.

Test step 6 - Voltage supply for A/C clutch -N25-, activation of Coolant fan -V7- and activation of A/C clutch -N25- Activation of A/C clutch -N25-)

Test Step 6.1:

Test Step 6.2:

Test Step 6.3, Part 1:

Test Step 6.3, Part 2:

Test step 7 - Outputs and inputs for certain vehicle equipment with diesel engine/for solar sunroof (not for USA)