Cooling fans only come on with the Ac

[20will20]

Hello I Cant seem to find a answer So I'm sorry if there is one I looked. I Have a 98 Talon TSI %100 stock an I have had it since new it has only 71000k on it. I have kept up on all maintenance. Ok so here is my problem i'm having if I drive it around town the car stays at the right temp but when I'm driving on the highway at speeds of 70/80 with the AC on or off my car wants to overheat. I've changed the t-stat , coolant an the temp sensor . But today I noticed that my cooling fans will only come on with my ac on. I'm Lost with what is going on any help ?? Thanks

 

[tomas123]

Sounds like a similar problem my dads old porsche had. I vaguely remember something about a switch.. But if you say it wants to overheat thats probably not going to be your problem

 

[20will20]

Car gets real hot but I never let it get to the point of it over heating so I really don't know if it really will overheat or not .

 

[tomas123]

Im not entirely sure how it works on dsms because i myself am pretty new so hopefully somebody with the right answer can chime in here and help you out. But in my situation regarding the porsche.. Somebody had hacked up the wiring of the cooling fan switch so the cooling fans ended up ONLY turning on when A/C was off and sometimes even when the key was in the ignition but the car was not started.. And also another problem i had with my old car was contacts corroding and causing it to nearly overheat.
Sorry i cant be much help

 

[20will20]

Its ok any info is good info thanks for the help I am going to look it tomorrow an hope I can figure it out.

 

[miguelmcv]

That's how it should be, it has to turn ON when you turn on the AC, the cooling fans will turn On when temperature sees it's target,.
Sounds like you have a clogged radiator, Try to flush it out and see what it comes out of it, also it can be your water pump, but first check your radiator.

 

[20will20]

I am going to try to flash out the radiator tomorrow an the temp gauge goes up to the top of the gauge.

 

[tomas123]

I just realized i was reading the OPs post the opposite way as described. (Facepalm) thought it was fans turned off when ac was on. On that note dont listen to me, going to sleep now. Good night and good luck! Total fail

 

[20will20]

But what I don't under stand is I can leave my car running in park and my car will get hot an my cooling fan will not kick on. so I have to turn on the ac to get the motor to cool down

 

[miguelmcv]

But what I don't under stand is I can leave my car running in park and my car will get hot an my cooling fan will not kick on. so I have to turn on the ac to get the motor to cool down

Got you.

There are 2 sensors at the thermostat housing, One is for the gauge temperature and the other one is for the fans, You might have a bad (fan) temperature sensor.

The gauge sensor has only 1 wire and the FAN sensor has 2 wires,, check that out, it might be off.

Discard what I said about the radiator.

 

[luv2rallye]

There are 2 sensors at the thermostat housing, One is for the gauge temperature and the other one is for the fans, You might have a bad (fan) temperature sensor.

The gauge sensor has only 1 wire and the FAN sensor has 2 wires,, check that out, it might be off.

^ Yes. On a 2g the ECU controls the fans based on the 2 wire temp sensor, AC switch, and vehicle speed: http://www.dsmtuners.com/forums/attachment.php?attachmentid=86862&d=1219990229

 

[miguelmcv]

http://www.dsmtuners.com/forums/attachment.php?attachmentid=86862&d=1219990229

Wow, That's identical to my Service Manual Book.

No wonder looked so Familiar.

 

[Purex2c]

Check the relay's.

 

[phunny]

Sounds like someone tried to wire it so both fans come on together and instead of using the temp sensor they wired it to the fan power.

 

[20will20]

Thanks For all the ideas. Ok so I flushed out the radiator put a new new temp sensor ,fan temperature sensor an checked all relays . Now I'm done An started up the car an let it run the fans still don't come on at all unless the ac or heat is on. In town driving temp stays good went on a back road with hills an car almost overheated had to turn the heater on to stop it. I'm so lost with the car

Sounds like someone tried to wire it so both fans come on together and instead of using the temp sensor they wired it to the fan power.

Car has been with me since new never messed with the wires to the fans it just started this 2 weeks ago.

 

[miguelmcv]

Well, we rull out the fan sensor, so next step is to check the lines from the sensor to the ECU, some times the wires get bad and doesn,t allowed the signal to get to the ECU, check the lines ti see if there is continuity on the line.

Edit,

Check line 83 (cooling temperature sensor), thats the line that goest to the thermostat sensor (fan sensor), check that the line is good.
Here the pinout from your ECU.

http://www.dsmtuners.com/forums/articles-tuning-ecu/281763-2g-turbo-ecu-pinout-w-wire-colors.html

If the wire is not good, the ecu will never cath the signal to turn the fans on.

If the fa. Relays are bad, they will never turn on, but I wouldn,t bother to check them which you stated fans are turning ON with the AC, unless you want to tr if the relays are OK before testing the wire which hecki g the relays is a peace of cake.

 

[20will20]

OK I found a wire that was split fixed it an fan now goes on An off as it should. But for some reason it still heats up at highway speeds but is fine around town. Could it be the water pump?

 

[phunny]

OK I found a wire that was split fixed it an fan now goes on An off as it should. But for some reason it still heats up at highway speeds but is fine around town. Could it be the water pump?

It could be anything from a water pump to a head gasket.