Rad fans not turning on.

[Sam1212]

Hi everyone was trying to get the ac working In my 2001 Jetta tdi with 285k.
I know that If the radiator fans won’t turn on the ac will not work so I read the thread on here about troubleshooting the radiator and condenser fans and I’ve ran into a dead end.
1st issue
When I press the AC button no light turns on, would that have something to do with the burnt out resistor that controls the fan speed, before my fan speeds stopped working the ac button would at-least light up obviously no ac though.
2nd issue
Since I can’t do the trick with turning the ac button on and seeing if the fans turn on I went to jumping the fans directly from the battery, big fan nothing little fan turns on with direct power but not in normal operation, after a drive where engine got up to temp I hooked up a meter to the output to the fans from the control module (with car still running) and nothing was reading from either one of them. Big or small.

What would the next step be? Trying to fix the first issue or replacing the control module and seeing what happens? Or something completely different. I’ve already checked the green fuses on top the battery as well and they look alright not sure if there’s a different way to tell if they are burnt out? Obviously know I need to replace the big radiator fan.

 

[Warthog]

Hi Sam. I was looking for info on a problem with MY A/C being intermittent and saw your post on radiator fans.
I have a 2000 Jetta, TDI, with 312K miles. Runs fine, BTW.
So far I have replaced the temp sensor on the engine head (G2+G62), The temperature sensor at the bottom of the radiator (F-18), the fan control module $$! and finally the switches in the dash...the fan switch was faulty.
Still, when I switch the A/C "ON" with the dash switch, the radiator fans do not come on...some of the time, maybe 20%. If I start driving, the A/C might start after a couple of miles. USUALLY after about 5 miles I will stop at the store and go in for 30 minutes. When I return to the car, the A/C will operate.
Sometimes the A/C runs from the cold start but later on, it decides to stop for a while. This is NOT in heavy city stop and go traffic.

I wouldn't replace the control module on a guess. It ain't cheap.

I hope someone will point us in the right direction on this. there are only 2 other sensors that I find on the schematics that provide input to the A/C and fan module: the Ambient temperature sensor (F38) and the A/C High Pressure Sensor (G65). I would sure like to know how the HP sensor can stop the fans for the A/C if it's not running at all...does it fail like this? But it ought not stop the radiator fans...

 

[BobnOH]

I'd suspect the G65. Could just be wiring/connects. I can tell you I ran mine with intermittent fans, killed the compressor after a couple years.

 

[ToxicDoc]

I chased a similar problem for 6 years. My guru finally found it by accident. There was a wire break at the temp sensor that would intermittently have contact then lose it. Look carefully at the wiring near all the harness plugs.

 

[Warthog]

OK TD. I had trouble with the connector on the MAF from corrosion....maybe THAT is the answer. Cleaned and used some special "grease" on it and no more trouble.
Will try and report back!

Logically, fan failure should stop the A/C but A/C problems should not stop the fans. Wish I had the logic inside the fan control module shown somewhere.