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Cooling fans

DavidL

DavidL

Active member
Can someone confirm to me:
Both fans run at both speeds. Mine is a 90G turbo and I have a suspicion that the fans are not running at the slow speed.
But I'm a little confused as to whether there is one slow and one fast fan or whether both run at both speeds?
I need to do a few tests and see what happens if I switch off when the fans are running. If the slow resistor is at fault then both will go off ( I think earlier cars only ran one fan with ignition off).

Anyone confirm or correct my thinking?

 
I know this was covered on here some time ago, but can't remember the answer. I'm not sure that there was a concensus reached ...

Search may be your friend. Or the knowledgeable types who knocked it about last time may well have another bash at it.


Oli.
 
David

I did some extensive poking around and interrogation of the PET wiring diagrams on this topic last year prior to removing one of my fans and installing an additional oil cooler.

Your correct the fans operate at two speeds which should be triggered by 98c & 106c (I might have these figures slightly wrong...) temperatures at the Rad mounted switch. In essence when the coolant gets hot the fans kick in, if the temp continues to rise, the fans go faster.

The wiring is simple to the fans & rad switch - 3 wires into each. There are also two other switchs in the system:

1. The cabin based A/C switch, when you activate this to kick in the electromagnetic clutch on the compressor unit also switches the fans on at low speed.
2. Situated in the pressure feed to the A/C matrix is a pressure switch - I believe that if the A/C gas gets above a certain pressure (ie not cooled sufficiently through the matrix) then the fans also kick in a low speed.

Good luck trying to decipher the wiring diagram ! I would suspect from your symptoms that its probably the rad based switch, but check the low speed operation by hitting the A/C button.

Yours

Chris
 
If I remember correctly the temps stamped on the switch I recently replaced ('90 turbo) were 92/102°C.

Maybe it should also be added that the low speed is controlled by a resistor pack located on the right side of the blower cluster, below the windshield - if these are removed and their wires shorted, then the fans will run in high speed as soon as coolant temp reaches 92°C instead of 102°C.

Chris, are you sure about fans running in low speed when engaging A/C ?
 
Thanks for clarifying the temperatures, I couldn't remember the exact figures.

Yes, I'm sure about the A/C switch kicking in the fans, as it still works on my single fan without the A/C system connected !

If you look through the PET wiring diagram for the Turbo (very complex and time consuming) it shows the dash switch for the A/C linked into the large relay that controls the fans.

Next time you start the car up (ie engine cold), hit the A/C switch and then listen/ see the fans kicking in !
 
Sorry, I did not express myself correctly - I know the fans kick in when pushing the A/C switch, but do they really run in low speed instead of high speed?
 
Yes, they only run at low speed to start off with - I understand this is to keep the A/C coolant at temp. Typically the greatest need for cool or A/C air is when a car is at slow speed or stationary.

Should either the radiator coolant temp (102C) or the high pressure switch in the A/C coolant open the fans will then run at high speed to drop the temperature. For this to happen you'd probably have to drive at pace (motorway or trackday) then drop speed to stationary/ very slow on a very hot day - large momentum of heat to dissipate.

IIRC, I very rarely hear/see my fan at high speed, having said that, I don't have an A/C matrix in front of the radiator and have straight through cooling on the RHS of the radiator AND a large front mounted secondary oil cooler, so my car doesn't tend to build up heat. Having said that, when I do stop the single fan works for a long time to drop the radiator temperature.
 
You are right... These days the fans run in high speed so rarely on my cars that it took me some time to remember how much louder they sound when running in high speed than when cruising with the A/C switch on.
 
Cheers chaps.
Clarkes is quite useful on this but I just need to remember he is talking about lhd cars.

My ac condensor has been removed so I don't know if the wiring is still in place. If the fan runs at slow speed then I suppose the motor is ok and I should check the fan switch and resistors. If it doesn't it doesn't actually mean anything.
I've just noticed that the gauge is getting to just over the 100 mark before it starts to drop and it seems to get warm quickly in traffic - fine on the run.
Something clearly still works but I suspect something isn't quite right.
Its off to promax in a couple of weeks so if I have no joy then I'll let them sort it.
 
David, I would suggest the following procedure to begin with :
http://www.clarks-garage.com/shop-manual/cool-01.htm#laterelaytest
 
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