both radiator fans running constantly

In prepping for a 2K trip next week, there couple of quibbles I need to address.

Both cooling fans run constantly. The AC is off. Engine cold, start up, and they both run continuously. Key off, and they both stop. Not sure about the different speeds, but I venture to say it is high speed. I suspect this is not normal. However, the AC does work good! I've only been driving this for the last month, and have never noticed this before. Maybe I have overlooked it, but I am sure to a reasonable degree it is a new occurrence. Any input on troubleshooting and addressing this? Thanks.

Coolant temp sensor or fan control module.

Would you happen to know the Ohm value for the coolant temp sensor? Or any other way to troubleshoot it? Or troubleshoot the fan control module? Thx-

http://forums.tdiclub.com/showthread.php?t=242699 look at the pdfs in the first post.

I would probably unplug the HP AC switch and see what happened, then plug it back in and unplug the high temperature switch in the top radiator hose, and see what happened.

Then go through the PDFs.

Thanks all. I will troubleshoot this evening and repair as needed.

I think you'll find the source of your issue if you patiently go through Dan's excellent diagnostic procedure. I have that same PDF printed and ready to go in my paper drawer myself, and have used it quite often, because it streamlines the process.

Thanks again, Dan!

Ok, after some troubleshooting with Dan's guide I have some conclusions...and questions.

I can unplug both fans and jump them to the batt. They both run on slow / fast.

I can jump the coolant sensor and get them both to run on slow, but not on fast.

When I unplug the AC (G65?) sensor the fans stop. This was the sensor mounted up near the firewall in the discharge line going to the evaporator.

This leads me to believe it is related to the AC, not necessarily the FCM.
noticed in Dan's guide it said to check the voltage at the white wire on the G65. It should be above VDC, and change proportionately with refrigerant pressure. The wire I have on this are Blue/red, yellow/red, black/white, and black/blue. Not sure which one to test.

I may also add in all the above tests, the engine was off, and AC was in the off position. Any further help would be much appreciated!

I think you had the wrong guide. Use the one for the older cars.
Your car is old enough to use a F129, four wire double switch, not the 3 wire G65.
It should not run when unplugged.

You can safely short (jumper pin to pin on the connector) a 4 wire switch for testing.
Jumper pins 1 to pin 2 (blue/red to black/white) for normal operation.

You should be able to jumper pins 3 to 4 as well. My reference material for this switch was hazy; it is not exactly clear to me if pins 3-4 being jumpered will simulate a high or low pressure condition. Maybe you could experiment and tell me?

You cannot simply say "I jump the coolant sensor" you have to tell me which one? Are you talking about the F163 AC cutout switch in the top radiator hose? (which is what I suspect.) Then jumping that simply lets the AC clutch engage and the fans run in slow.

To test the FCM you have to jumper the switch mounted in the radiator, the F18, switch, as in the fan troubleshooting guide. For slow speed the FCM is not used (from this temperature switch) and it will work with key off or key on. For fast speed the key must be on, and the FCM must function.

It surely sounds to me as if the radiator thermoswitch is stuck in "very hot" or there is a wiring issue between the radiator thermoswitch, or the FCM high speed fan relay is stuck on.

Look for an email.

Wow Dan, you are the Fan motor king! I am scrambling to get this resolved before our trip next week. I realize this isn't the worst thing.

Yes, I do have the 4 wire switch. It is mounted up near the fire wall. To be clear, when this is unplugged, the fans both stop.

I will keep you posted as to the pins 3-4 being jumped. I was hesitant to jump any of these no knowing exactly what they are.

As for jumping the "coolant sensor," sorry, wrong nomenclature. I was referring to the radiator thermo switch. 3 wire switch mounted about half way down the radiator. This I can jump and get the fans to run slow, but not fast. Nothing happens on fast.

It seems to me, if the radiator thermo switch was stuck in "very hot," I should still be able to unplug the harness for it, and jump the pins to get both to run on high. I did check all the fuses you mentioned. All are good, and very clean. Any idea where to go from here? Troubleshoot and check the 4 wire AC switch? Thanks again for weighing in with your experience

I would do a close inspection of the wiring to the FCM and the radiator thermoswitch.

Do you still think the fans are running constantly in FAST speed after seeing the different speeds in your testing?

One thing, with the key off they should not be capable of running in fast, no matter what.
If you jump pins 1-2 of the 4 way switch (with the connector unplugged), and everything then works normally, that would mean the F129 switch is bad, I think.

Hi again Dan. I see a flaw in my troubleshooting from your last post.

I need to test the radiator thermo switch for fast fan speed with the IGNITION ON. I was checking this with the key in the off position.

I will then proceed to jumping pins 1-2 of the F129 switch. I will keep you posted shortly-

That 4-pin refrigerant pressure switch was a common failure on the A3 cars, and its failure mode would cause the fan to run constantly. Never seen it manifest itself in the same manner on an early A4 car, though, but that doesn't mean it couldn't happen.

I'm not sure how similar the two systems are, though. I know the early A4 car is sort of full of leftover A3 bits though, so maybe...

I saw this on a TDI last year when replacing a clutch master and diagnosing low power, which turned into fixing a botched timing belt replacement. The owner said the previous garage (who did the timing belt) said it was 'normal' for the older cars to do it.

I did some diagnosing and found two tires chafed through. Just a thought if everything else checks out.

Thanks for the tip off Abacus. Do you happen to recall where you found the chaffing in the wiring / harness? Thanks-

In the harness within a few feet of the sensor. It was hidden pretty good and I only found it by touch. Just seeing the harness isn't good enough, you need to run your hands & fingers down every inch to feel for anything weird.

Well, I must thank all for there input here on this. It looks like it was a bad 4 pin AC switch. The fans keep running on fast even with the Rad thermo switch unplugged. I unplug the AC switch and jump out pins 1-2, and the rest of the checks test out good. ( rad thermo switch of fast and slow) I have ordered a new AC switch, and also a radiator thermo switch for good measure. It seems from the long post on cooling fans this can be a troublesome failure point with disastrous consequences if not noticed. So, I will swap out as it looks original. Nice to find a good group that is very knowable and willing to weigh in with their input. Thanks again for the help with troubleshooting!

cooling fan issue

Hey i have a similar issue but a little different. I have a 2000 jetta tdi, and my cooling fans are always on even when the motor is cold as long as the ac switch is on. If i turn the ac switch to off both of the cooling fans turn off. I noticed this issue right when it got cold here in Spokane Wa and the car started taking way too long to fully warm up ( like 20 min of driving before it warms up) then i noticed the fans always staying on since i always had the ac switched on, and that the fans quit when the ac is switched off. Is this normal for these tdi's ? Any help is much appreciated.

serge777 said:

Hey i have a similar issue but a little different. I have a 2000 jetta tdi, and my cooling fans are always on even when the motor is cold as long as the ac switch is on. If i turn the ac switch to off both of the cooling fans turn off. I noticed this issue right when it got cold here in Spokane Wa and the car started taking way too long to fully warm up ( like 20 min of driving before it warms up) then i noticed the fans always staying on since i always had the ac switched on, and that the fans quit when the ac is switched off. Is this normal for these tdi's ? Any help is much appreciated.

Click to expand...

Pretty sure what you describe is normal.

serge777 said:

Hey i have a similar issue but a little different. I have a 2000 jetta tdi, and my cooling fans are always on even when the motor is cold as long as the ac switch is on. If i turn the ac switch to off both of the cooling fans turn off. I noticed this issue right when it got cold here in Spokane Wa and the car started taking way too long to fully warm up ( like 20 min of driving before it warms up) then i noticed the fans always staying on since i always had the ac switched on, and that the fans quit when the ac is switched off. Is this normal for these tdi's ? Any help is much appreciated.

Click to expand...

Absolutely normal. ANYTIME the AC is on, both fans should be on.

The fans are not increasing your time to warm the engine. The thermostat keeps the coolant from going to the radiator. Diesels warm slowly. In 25 degree weather it would take 12 miles to open the thermostat on mine, on a stop and go country drive of 55 mph or less. But I would get warm air out of the heater in a few miles - warm enough to defrost with.

If you hit the interstate, though, it only takes a couple of miles to get the Thermostat to open.

Thanks Dan. That makes sense.

Cooling fans won't stop!

Hello,

I have a 1.9 TDI 1998 Golf 4.

I recently encountered a problem with the cooling system. The car is off, but the fans won't stop. They spin until the battery dies.

Any thoughts?

Thanks

G

Fuse on top of the battery. When mine did this, I got away with simply cleaning it up, it was a corrosion mess. That was a long time ago, still working. Sometimes it will destroy the holder and/or wiring.