OM603.971 aux fans engage when?
 

Hey all
I was under the impression that the aux fans should engage when the AC comes on, is this correct?

My aux fans do not come on at present when I turn on the AC. I have to pull the connector to the water temp sensor (two wire) to get them to come on. When I return the connector to the sensor they stay on, even if I turn the AC off. This doesn't sound correct to me.

Any advice or testing procedure I can do? I really need these fans to operate properly now that I have functional AC.

Thanks
Steve A

Climate control turns the aux fans on in low speed mode when a pressure switch in the refrigerant is tripped. This does not happen as soon as you turn the a/c on. If the switch is defective, the fans won't turn on at all. If there is plenty of air passing through the condenser (due to the car's motion), the fans may not turn on either. My '87 300D Turbo (W124, OM603) seems to turn the fans on when the car is moving slowly (in traffic) or parked.

If the switch is defective, it must be replaced, which requires evacuating and recharging the refrigerant, unfortunately.

Jeremy

Thanks for the info, I'll see if I can test the refrigerant switch. The car never exceeds 90C temp, or hasn't yet but the fans do not come on. I wonder if the system isn't fully charged whether that affects the switch.

Evacuating the system isn't a big deal, we just did it a short time ago to install a replacement compressor, it's just annoying to do it now again after I just filled it.

Thanks
Steve A

The shops test the switch by shorting across its terminals with the car running and the a/c on. If the fan starts when the switch terminals are shorted, the switch is blamed. Low refrigerant will prevent sufficient pressure from building up in the lines to trigger the switch.

Your engine also has a switch in the water jacket to turn the electric fan on high speed when the coolant reaches 105C or thereabouts. There are four different switches with different temperature specs -- was just discussed here in another thread a couple of days ago.

Yes, it's a pain to have to recharge the system just because a switch failed. Some folks have been known to put in a manual switch as a temporary fix. The a/c is most likely to need additional air in slow or stop-and-go traffic.

Jeremy

Jeremy

Thanks for the info and advice, seems my concern was premature. The aux fans appear to be running properly and probably have been all along. I just thought they were to come on when the AC was engaged but that's not the case.

At any rate they have been coming on and going off appropriately now that our temps here have gotten higher and the engine is running hotter. They are also pretty quiet so one really never knows when they engage / disengage so at this point I think all is well.

Thanks again

Steve A