Slow speed

Slow speed

For the fans to operate, the ’fan relay’ output from the ECM must provide an earth on the S/U wire to energise condenser fan relay 2 and the separate cooling fan relay. When these two relays are energised, battery voltage on the P/U wire from fuse 4 in the engine compartment fuse box is switched via the closed contacts of the separate cooling fan relay to the common of condenser fan relay 2, within the air conditioning relay module on the U/P wire. Since condenser fan relay 2 is also energised, battery voltage is switched on the P/S wire to one side of the condenser fan. The other side of the condenser fan is connected on the U/S wire to the common of de-energised condenser fan relay 1, via the contacts of the de-energised cooling fan relay, to the cooling fan on the S/U and U/P wires. The circuit is completed by an earth on the B wire to the other side of the cooling fan. Both fans are now connected in series and will be operating at slow speed.

Fast speed

When the engine temperature reaches 112C the ECM ’fan relay’ output (Non-Bosch ECM) or the high temperature switch (Bosch ECM) provides an earth on the U/Y wire which energises condenser fan relay "1" and the cooling fan relay within the relay module. This switches battery supply on the N/W wire via the contacts of the cooling fan relay to the cooling fan motor on the S/U and U/P wires. Simultaneously an earth is switched via the contacts of the condenser fan relay "1" on the U/S wire to the condenser fan motor. The other side of the motor already has battery supply via the contacts of the condenser fan relay "2" on the P/S wire.

Both fans are now connected in parallel and will now be operating at fast speed.