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sprinkles08
sprinkles08, ASE Certified Technician
Category: VW
Satisfied Customers: 21599
Experience:  ASE Master and Advanced level certified. Factory trained with 15 years dealership experience
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02 jetta wagon 1.9 tdi a/c does not run and radiator fans

Customer Question

02 jetta wagon 1.9 tdi a/c does not run and radiator fans run continuously while engine runnig and after shutdown even when engine is cold?
Submitted: 1 year ago.
Category: VW
Customer: replied 1 year ago.
Also ac pressure good at 85 psi, no diagnostic codes . Thermal rad switch is working properly.
Expert:  sprinkles08 replied 1 year ago.

Hello and welcome to JustAnswer!

It sounds as if the compressor may be disabled due to a coolant temperature sensor signal issue. If coolant temperature is high or the ECM has identified that the signal is implausible then it will run the cooling fan all the time for protection and can disable the a/c compressor. If the cooling fan is running with the key off though that would indicate a failure in the fan controller or a short to ground on it's control circuit.

With the engine cold use a scan tool to compare engine coolant temp to ambient and intake temp. If the temperature is incorrect then you either have a failed coolant sensor or sensor wiring/connection issue.

Customer: replied 1 year ago.
My scan tool does not read sensors can I test with vom
Customer: replied 1 year ago.
Fan module replaced ,either original or new module do same thing running after key off.
Customer: replied 1 year ago.
What do you mean by short in control circuit, in module or external.
Customer: replied 1 year ago.
I assume coolant temp sensor is a thermistor what resistance value can I expect at 70 degrees f.
Expert:  sprinkles08 replied 1 year ago.

If the fan runs after the key is off then the fan controller is bad or it's control circuit is shorted to ground. That should be separate from the a/c issue. Did the replacement do the exact same thing as the old one immediately when plugged in?

Customer: replied 1 year ago.
it did exact same thing fans on all the time.fans shutdown if module 14 pin connector is disconnected ,then fans will cycle on/off on thermal switch when car idling.
Expert:  sprinkles08 replied 1 year ago.

With the key off if you unplug the ECM will the fans shut off?

Customer: replied 1 year ago.
Do you have a temp to resistance to ck coolant sensor?
Expert:  sprinkles08 replied 1 year ago.

The correct way to check coolant temperature signal is by using a scan tool. Testing the sensor's resistance isn't that accurate and doesn't account for the wiring. At 85 degrees it should be 1500-2,000 ohms; however if the fan runs without the key on then the coolant temperature signal is no longer in question because you have a failed fan controller or shorted control circuit.

Customer: replied 1 year ago.
Ok please elaBorate on troubleshooting shorted control circuit if you can? I will rate u very highly if we can get to bottom of this nightmare. Thank you for your help
Expert:  sprinkles08 replied 1 year ago.

I asked this morning if the fan turns off if you unplug the ECM while they are running with the key off but never heard back.

Customer: replied 1 year ago.
Either way you will get good rating.i do appreciate your persiverance.
Customer: replied 1 year ago.
I was out for a bit in garage now testing fan module i/o 's
Expert:  sprinkles08 replied 1 year ago.

Does it stop running with the ECM unplugged?

Customer: replied 1 year ago.
Where is ecm located on tdi
Customer: replied 1 year ago.
I'm accessing ecm now I'll get back shortly
Expert:  sprinkles08 replied 1 year ago.

Ok.

Customer: replied 1 year ago.
After shutdown pulling ecm plugs DOES NOT SHUTOFF FANS
Expert:  sprinkles08 replied 1 year ago.

You mentioned testing the controller's inputs and outputs. What were the results there?

Customer: replied 1 year ago.
Hello .fyi ac not running and fans running continuously were caused by same issue. The ambient temp switch had 1325 ohms at 70 degrees. I jumped plug and car is fixed I appreciate your help and will pay the , 28 dollars but the fan module test procedure I found on Web found the issue
Expert:  sprinkles08 replied 1 year ago.

I'm glad you got it repaired.

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