Radiator fan

[Aid24]

Hi all, first time I've posted on any forum but hope you can help. I have a 1999 1.9d that is running a bit warm. Radiator and thermostat replaced but what I have noticed is that it has two fans but only the fast one is kicking in when guage gets to three quarters. It doesn't have ac. I can't seem to find any information on relays etc anywhere. Any help greatly appreciated.

[Kieron G]

I wasn't aware there was a difference with the cooling fans. I think to start with i would check the supply to the second even with a test bulb and check motor isn't faulty when the engine is warm enough to switch them on. Then maybe a temporary supply to the motor to check how it runs and the earth isn't bad. Obviously you would have to watch your fingers

[Sol]

I've attached the drawings for the cooling circuit fan control below, seems on the M49 the fans are on relays 1508, 1509 & 1504 which are mounted on the front of the fan assembly next to each fan on the outer face near the top. Looks like they work in a mutually exclusive way, so fan one (low speed) runs alone, then when the ecu wants to switch over to high speed it takes power away from the LS fan and grounds pin 2 of the high speed so they only run one or the other, never both at the same time. 

So if the high speed one is running, then the low speed one has automatically switched off and passed control to it. I guess the LS relay (or the ground connection MC12) is perhaps flaky and when low speed should be on, it isn't running and you only become aware when it switches over to high speed.

157 looks like LS and 154 HS from the drawings. There are two Maxi fuses E and F which power the switched feed to the fans respectively.

See the attached PDF and let me know if this all makes sense. The relays are shown in their default position.

Edit: more info, 1508 is Low Speed relay, 1509 is high speed relay, and 1504 is listed as left and right hand fan series supply relay. C001 is diagnostic connector, BMF2 is the Maxi fuse unit, as is BMF1. 4040 is the coolant sensor - 8010 is the coolant temperature control unit.


  M49 Fans.pdf (Size: 1.04 MB / Downloads: 3)

[Kieron G]

Thanks for that post Zion. Good bit of information which I might need one day