smddanny

I have a farily new to me 993TT and I need to make a couple of repairs. It appears that an engine cooling fan that draws cool air in thru the intercooler has a control system issue. I have heard it short cycle a couple of times and it was running last time i turned the key to ignition on and the motor was stone cold. Don't recall this behavior on my last 993 T and don't think this is correct. Does anyone have a schematic or know of a link to a schematic on a 96? Is this cooling function a centrallised control function of the ECU (woundn't think so) or is there a locallised control function with an rtd or other device hidden in the motor compartment?

Thanks in advance,

Danny
'96 993 TT
'68 soft window targa (since 76)
Lotus europa 73 TCS
BMW 3.0 CSI 72 garage queen

sold
85 930
pair of 68 911s
72 RS replica

Greg Fishman

Check http://p-car.com/diy/fan/ . Lots of info on the oil cooling fan, my guess is the ballast resistor.

smddanny

I can see from some searches that there is no simple answer to this. The fan I am refering to is located below the intercooler. This fan is controlled by the CCU in the dash (possibly?) in concert with some other controls that provide a cooling function to the motor compartment. I will experiment with the CCU contols and see if I can induce some other behavior in this fan. Any tips welcomed.

Thanks
Danny
96 993T

Jay993turbo

I believe there is a temp sensor in the hot air manifold that causes the heater blower to cycle on. This usually happens when the car is sitting after shutdown and the heatsoak causes the temps to rise in the engine compartment.

JasonAndreas

With the ignition turned off the first-stage of the rear blower fan should operate if the temperature inside the plastic ducting goes above 75'C and will then shutoff at 70'C but only for 20 minutes. After 20 minutes it should turn-off no matter what. If its not then you might have a bad transistor inside the CCU (T1 located on the lower PCB towards the rear and next to the relay). Did you notice if the small fan located behind the CCU operates continuously or does it shut-off after 20 minutes? You'll hear a buzzing from behind the ccu/dashboard if its running. Maybe the first thing you should take a look at is the NTC (negative-temperature-coefficient) sensor in the ducting and measure its resistance? I'm hoping you can do so without removing the intercooler? Otherwise you could pull out the CCU from the dashboard and measure the resistance between pin 10 and 18 on the upper (larger) connector.

0'C (32'F) 28.8 - 36.4 kOhms
25'C (77'F) 9.0 - 11.0 kOhms
50'C (122'F) 3.1 - 4.0 kOhms