Slow speed

Slow speed

For the fans to operate, the ’fan relay’ output from the MEMS control unit (T-Series 2.0) or the low temperature switch (L-Series) must provide an earth on the U/Y wire to energise the cooling fan relay 2 which already has battery voltage on one side of the coil. When this energises, battery voltage on the N/G wire from fuse 28 in the engine compartment fuse box is switched via the closed contacts of cooling fan relay 2 to the cooling fan on the P/S wire. The other side of the cooling fan is connected on the U/S wire to the common of de-energised cooling fan relay 1, via the contacts of the de- energised condenser fan relay, to the condenser fan on the U/S wire. The circuit is completed by an earth on the B wire to the other side of the condenser fan. Both fans are now connected in series and will be operating at slow speed.

Fast speed

When the engine temperature reaches its predetermined value, the ’fan relay’ output (MEMS control unit) or the high temperature switch (Bosch ECM) provides an earth on the S/U wire which energises the condenser fan relay and cooling fan relay 1 within the relay module. This switches battery supply from fuse 33 on the N/U wire via the contacts of the condenser fan relay to the condenser fan motor on the U/S wire. The other side of the motor has an earth permanently connected on the B wire. Simultaneously an earth is switched via the contacts of cooling fan relay "1" on the U/S wire to the cooling fan motor. The other side of the motor already has battery supply from fuse 28 via the contacts of the cooling fan relay "2" on the P/S wire.

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