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low fan speed control

1K views 12 replies 3 participants last post by  .:ian:. 
#1 ·
hi all,

sat in traffic today my temp rose past 90 ( only a bit) then the fan kicked in full speed to bring it back to 90...then I noticed, I have never seen it go to low speed....

so what do I need to buy to sort that? im guessing its the green thingy stuck in the front of the fan shroud? are the two plugs on that directional? as they can fit either way and I've no idea what way they should go.

and finally...where do I buy one? :)
 
#2 ·
also, after reading some other threads...I hear the full speed very rarely kicks in...is what I am seeing and hearing the low speed? the temp gauge goes about 2mm past 90 then I hear it kick in and bring it back down to 90.

when does the low speed kick in and when does the high speed kick in?
 
#4 ·
I`m sure my fan initially cuts in just before the 90 mark and full speed just after, though given the inaccuracies in these dials, thats not much help on yours I suspect.. The green thingy is a resistor so it doesnt matter which way round it goes, if you unscrew it from the fan housing and have a look you should see if its ok or not.

If you have a multimeter, it should be almost a complete short (something like 0.3 ohms) but a visual check should be enough.

Mine had both failed, one had a crack in the resistance wire, the other melted one of the connectors. I rewired them with nichrome wire (300mm of 18swg) and 4mm bolts and various crimp connectors. Should outlast the car as the original wire crumbled away on removing it and the new stuff was hard to bend around the former!
 
#6 ·
The resistor is the only thing that provides the low speed. Basically the fan is built to operate at a single speed (the high speed) and putting a large resistor in series drops the voltage so slows the fan. If the fan is otherwise ok on high speed the resistor is almost certainly the problem.

Unless you have a multimeter the only check you can do is a basic continuity check.

Using a bulb with something like a torch battery, the bulb should light without the resistor in circuit. Put the bulb with the resistor in the line to the battery. Failure for the bulb to light will show if the resistor has blown (open circuit).
 
#7 ·
thanks,

if I were to short the two wires that connect to the resistor and run the engine, should the fan spin slow before getting to temp? if so I have just tried that and I get nothing at all??

i just took the resistor off, looks in very good condition..but then I noticed where the coil joins onto the pins one side the spot weld has come off so not connected..so I have just cleaned it up and resoldered both sides so will go out and re-test in a while.
 
#8 ·
thanks,

if I were to short the two wires that connect to the resistor and run the engine, should the fan spin slow before getting to temp? if so I have just tried that and I get nothing at all??
The fan will immediately run at high speed but only if the engine temperature is at or above normal and therefore requires cooling. If you got nothing it should be because the engine temperature was fairly cool.

i just took the resistor off, looks in very good condition..but then I noticed where the coil joins onto the pins one side the spot weld has come off so not connected..so I have just cleaned it up and resoldered both sides so will go out and re-test in a while.
.
Providing you now have a good connection it could now be ok.
 
#11 ·
Early cars had the two speeds controlled by a 2 level switch stuck in the rad that grounds either relay i99 (low speed) or i100 (fast)
Later cars the relays are controlled by the ecu.
It could be the 2 level switch, relay i99, or the wiring.
On the diagram in the workshop manual I have it also shows relay i99 taking its power from the aircon feed, via the 30amp fuse Q39, whereas the full speed fan is energised via F17.

Do you have a multimeter?
 
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