Cooling and condenser fans

Cooling and condenser fans

The ECM operates the two fans together at one of two speeds. Low speed is achieved by connecting the fans in series and high speed is achieved by connecting the fans in parallel. The fans operate at low speed when either the compressor clutch is engaged or the engine coolant temperature is between 92 and 99 °C (198 and 210 °F). The fans operate at high speed when either the engine temperature is in excess of 107 °C (225 °F) or the medium pressure switch in the trinary switch detects a system pressure in excess of 18 bar (261 lbf.in²). When refrigerant system pressure exceeds 18 bar (261 lbf.in²), the medium pressure switch closes and connects the UG wire, between the ECM (C0159) and the trinary switch (C0279), to earth on the B wire between the trinary switch (C0279) and the earth point (C0564 on LHD) or earth header (C0017 on RHD).

On receipt of an A/C request, the ECM (C0159) earths the US wire from the A/C relay pack (C0173) to energise cooling fan relay 2. The energised cooling fan relay 2 connects the feed from fuse 6 of the under bonnet fuse box to the PS wire between the A/C relay box (C0172) and the cooling fan motor (C0005). The feed passes through the cooling fan motor (C0005) to cooling fan relay 1 in the A/C relay pack (C0172) on the US wire, then from cooling fan relay 1 to the condenser fan relay. The condenser fan relay connects the feed to the SU wire between the A/C relay pack and (C0172) and the condenser fan (C0280). The condenser fan (C0280) is earthed on a B wire connected to an earth header (C0017). With the fans connected in series, they run at slow speed.

If the engine temperature or system pressure increases to their respective switching points, the ECM (C0159) earths the UY wire to energise cooling fan relay 1 and the condenser fan relay in the A/C relay pack (C0173). The energised cooling fan relay 1 switches the feed from the cooling fan motor to earth on the B wire between the A/C switch pack (C0172) and the earth point (C0564 on LHD) or earth header (C0017 on RHD). The energised condenser fan relay switches a feed from fuse 5 in the under bonnet fuse box to the SU wire between the A/C relay pack (C0172) and the condenser fan (C0280). With the fans connected in parallel, they run at high speed.

Recirculated air

With the fresh/ recirculated air switch in the fresh air (off) position, current flows from the fresh/ recirculated air mode motor (C0413) to the fresh/ recirculated air switch (C0750) on the Y wire and to earth on a B wire between the fresh/ recirculated air switch (C0750) and an earth header (C0017). With the fresh/ recirculated air switch in the recirculated air (on) position, current flows from the fresh/ recirculated air mode motor (C0413) to the fresh/ recirculated air switch (C0750) on the K wire and to earth on the B wire; the tell tale illumination in the fresh/ recirculated air switch is also earthed on the B wire and illuminates to indicate the position on the fresh/ recirculated air mode motor.