Check your radiator/condenser fan operation NOW

Mike,
I'm in the exact same boat you are, my friend. The fans work fine with the jumper between 1 - 2 on the thermoswitch, but nothing between 2 - 3. I replaced the FCU, like you and still no luck. I have tested both fans slow and fast and the fans are good. The ambient temp sensor is reading 0.3 ohms. Next I'll run the vag-com output tests. But it sounds like I'm having the EXACT same symptoms you are. My meter won't read duty cycle either, but my charge pressure is good. It's a stumper...
And Dan, thanks so much for the OP. Those troubleshooting steps certainly helped, now if only I can find the smoking gun....
Mike

Some basic information, numbers and safety tips

This post is not aimed at recent posters; I just placed it here after reading some other posts in other threads. Some people are doing dangerous things - adding refrigerant with only a suction (low) side pressure gauge on a can.

Remember this is for Mk IV cars.

Our cars do not have a switch or sensor on the low pressure side of the system. This is not a 95 Suburban - systems have changed a lot.


The compressor suction pressure can range as low as 17 psig per the Bentley; I see 25 to 35 most often here in South Carolina when it is warm enough for people to be checking the AC system out. But suction pressure has very little to do with how much refrigerant charge you have - almost nothing, in fact.


Our AC systems have a high pressure sensor that provides fan control and compressor interlocks.


If HIGH side pressure drops below 15 psig, the compressor turns off, when it gets above 70 psig it turns on (clutch engages) again.


If HIGH side pressure gets up to about 450 psig the compressor turns off, it turns on again at about 350 psig.


If High side pressure gets up to about 550 psig then the safety valve blows off - if this fails then something breaks - often with disastrous results.

Cycling on the high pressure interlock. This is not a healthy place to operate. For actual pressure to get this high you have either severely overcharged the system or temperatures a much too high (your fans are not working, or the condenser coils are fouled.)


If it is due to overfilling the system and your high pressure interlock delays about 100 milliseconds then you will blow off your relief valve. If that fails then in another 50 milliseconds you will explode your compressor or line - it runs about half and half.


It is DANGEROUS to fill a system with only a low pressure gauge. Those cheap kits can destroy your AC system or kill you.


The ONLY proper way to charge a system is to evacuate it, then add a known quantity of oil and refrigerant.


I think that you should either do your homework, and buy the minimum equipment to safely do the job, or leave it to experts.


You can educate yourself on basic car AC refrigeration cycle operation in a couple of hours. Our systems are the more modern systems that have Thermal expansion valves (not orifices) and high pressure sensors (not low pressure switches).


You can then study up on troubleshooting details of our systems by reading the documents linked in post #1 here. These were not written for study guides or system instruction and are poorly written even for their intended purpose - but they are the best I can point you to.

Mike and Mike,
I am sorry you are having troubles.

Have you both verified that you have over 70 lbs pressure on the high and low side with the engine and AC off?

If your fans are not kicking on in fast speed from the radiator thermoswitch with the KEY ON, then I too would have suspected the FCM. If you put 12 volts onto T14/7 and the key is on, then the fans should kick on in high speed. You know you have 12 volts at the thermoswitch, but is the wire bad to the FCM? Note that this fault will NOT prevent your AC from operating.

But the key ON signal must also get to the FCM, have you done the following steps?

7) Check for 12 volts at pin T14/9 (unplugged).
a. This voltage is a switched ignition source and will have 12 volts when the ignition is in the "on" position. (Through fuse 5.)
8) Check for 12 volts at pin T14/4 (unplugged).
a. This is a constant battery source and should read 12 volts at all times from fuse S16.

These last two faults will prevent your AC system from operating.

I would also verify that you have 12 volts right at the fan motors, by sticking a pin through T3/3 and measuring to ground, while you are jumpering from pin 2 to pin 3 in the radiator thermoswitch.

Lots of reading this has been but tons of helpful info.
My 03 1.8T Jetta has been acting up, over heating in traffic with AC on. I found this thread, did the fan test a few days ago and discovered that the driver's side fan was inoperative. So I was planning on taking it out tomorrow and possibly trying to repair it. Today I decided to try the test again and this time none of the fans worked on low speed. I started the car and the ac started blowing cold but then went warm. I took the car around the block and came back to find the passenger side fan was now on. Is there a quick way just to determine whether its in low or hi spin cycle? Its strange the past 2 times I did this test the passenger side low speed fan worked and now nothing. Looks like I got some more reading on my hands.

Thanks everyone for all the info thus far

Brandon

The only way to tell fan speeds is by experienced ear, or by a Strobotach to measure speed.
If you do the radiator thermoswitch test (fan test pdf in post #1), you can gain experience for your ear.

Thanks Dan.

Is it a common symptom for one of the fans to work intermittently during the low speed fan test?
I guess I was hoping it was as easy as a fan replacement/repair but now neither come on for the low speed test :/

It is common for slow speed fans to be intermittent.
Tap the back of it, and it will often work for a while.

Alright -- I started off with only the small fan would do high speed - So I replaced the large fan and the FCM and both fans come on slow with key on and AC on ... Now I start the car and the clutch will not engage. I have replaced the high pressure sensor and all so the fan thermal switch. At the clutch I have 3.8 ohms and my pressures are perfect and so is refrigerent level. I am at a loss -- I have checked all my power and grounds and even cleaned my grounds. Any suggestions?? I checked continuity from the compressor to the 14 pin connector as well as ground ALL ok .. PLease help

Hi guys, just stumbled into here whilst trying to research an ac issue.
Been driving vws about 12 years but this is my first tdi.
2002 jetta with poor ac function.
Thanks to this great threadI figured out that one of my fans was dead.
Replaced that, but still poor ac.
Compressor runs, LP and HP pressures look fine.
Followed the instructions on the first post and discovered neither fan ran in high speed.
Unplugged the thermoswitch and jumped pin 2 & 3 . Fans ran at high speed with no issues.
Am I correct in assuming this points to the thermoswitch being shot?
Also, any links to the part online. Local dealership wants $65 and tax. This seems steep.
Thanksin advance.

Magnet,
The fans run in high speed when:
1) The AC system pressure is higher than normal.
2) The thermoswitch calls for them to run.

The only fast speed fan test I recall is the one you just ran and passed. When are your fast speed fans failing to run in fast?

If you have normal high and low pressure refrigerant pressure then the most likely failure is your temperature mixing doors. Either the cable that operates the door has come off or the foam has disintegrated that covered the wire mesh temperature door.

Thanks alot for the great work & writeups.
My A/C died yesterday - totally my fault as I knew I had a bad fan on the driver's side. I had some wiring for my fog lights that became entangled in the blades of the fan and it burned out very quickly about 2 months ago. I work so much am so busy I left it, now I'm eating sand for not taking care of it sooner. The A/C still worked well, till yesterday when I had been up all night making Jam, had to work dayshift and had a nap in the car with it running, the A/C on. I know its not good to let your car idle that long, but desperate times... Right at the end of my 'nap' I smelled something burning, noticed all of a sudden the A/C was blowing warm. Definitely an electrical burning smell when it happened. I have a spare compressor at home, so I figured easiest thing to do is to try changing out the compressor clutch, which I did - glad I did because my original looked horrible, with tons of small cracks throughout.
Made no difference though, its not engaging. Tomorrow am buying a parts car, will use the fan from it to replace mine. What I'd like to know is, what likely burnt out to cause that smell?? The compressor itself? The fan control module?
I believe the pass. fan still operates, wouldn't likely be the FCM if that is the case no? Just trying to narrow it down some. I will be bringing it in if it does being the compressor, I don't have the skill/tools to evacuate the system responsibly, or to recharge it. Any and all advice appreciated.

You are correct that if your remaining fan works in slow then the FCM is sending power out of the contact that supplies both fans in slow.

Was the smell stronger in the cabin or outside?

What was very likely is that the remaining fan(s) was(were) rapidly cycling off and on in fast speed. This often results in overheating and damage to the fuse panel on top of the battery.
Everything in the fast speed ciruit will get hot when they start cycling. Fan motors, wiring, FCM fast speed relay, fuses - all gets challenged and can fail.

But usually the weak link is the wiring to the fuse panel, the connections inside the fuse panel.

WoW hats off on the response time, you should be charging for this.
The smell was inside only, I didn't even lift the hood after it happened. I hate wiring, its like chasing a squirrel on acid. I like wrenching...
I had a look at the fuse panel on top the battery tonight after changing the clutch, nothing burnt or crispy looking. I'll do some easy testing as per your writeup tomorrow, I'm thinking the compressor cooked its electrical stuff, the resistance test will determine that I suppose. 4 ohms across the 2 posts correct?

Guess I'm glad am getting a whole parts car, probably end up replacing alot of electrical stuff on the car.

This is a bit of a follow up to my previous post.

I came here originally to determine an overheating problem on my 2003 Jetta 1.8T Automatic (TIP)..so I'll post up some info in case other 1.8t people wonder over.

I did the fan test and none of my fans were spinning at low speed but if i 'helped' the passenger side small fan it begin to turn. I decided to replace the fans.

Now I'm not sure about the automatic TDIs (my TDI is manual), but the 1.8T autos have clearance issues and therefore require a slimmer fan and shroud. These fans turned out to be considerably more then the regular manual fans. I took apart the old fan motors and decided I could get away with cleaning up the small passenger side fan and reuse it. I purchased a new larger driver side fan.

To install them it's fairly easy.
Jack up the front of the car and support it with jack stands. Both the fans come out in the should. The shroud is held in by 4 torx screws on each corner. Un-clip the 2 fan connectors at the bottom of the shroud and remove the 2 bolts holding the afterrun coolent pump in on the top of the shroud. Now you'll be able to work it around a couple coolant hoses and out the bottom.

I replaced the larger fan and cleaned up the smaller one and to my delight.. success!

Big thanks to DanG and all the others in this thread

DanG144 said:

Magnet,
The fans run in high speed when:
1) The AC system pressure is higher than normal.
2) The thermoswitch calls for them to run.

The only fast speed fan test I recall is the one you just ran and passed. When are your fast speed fans failing to run in fast?

If you have normal high and low pressure refrigerant pressure then the most likely failure is your temperature mixing doors. Either the cable that operates the door has come off or the foam has disintegrated that covered the wire mesh temperature door.

Click to expand...

Thanks for the fast reply, wow you guys are good.

But now you have me thinking. I mentioned the fan speeds because they never go to high speed. 100 deg f outside, ac full on and the fans only ever run at the lower speed. It was a surprise to see how fast they actually went once I jumped the thermoswitch.
But, you mention the foam, have noticed foam blowing out of the vents on occasion. Is this something we can investigate further? I have adreaded thought that this is going to involve removing the dash.

Thanks again for the advice.

When all is normal, you never see the fast speed fans run. At least I never do. If the fans ever cycle to fast, something is usually wrong.

If you have foam blowing out the vents, and normal pressures on your AC, you do not need to investigate further. You need to fix the doors.

Thanks for the advice. We will look into it.

DanG144 said:

Yes, that would seem to indicate a problem in that wire set. That resistance check from t14/10 to ground should be done with the AC compressor two wire connector plugged in.

Just to second check, was your clutch coil resistance ok when checked at the two pin connector local to the compressor? but when you plug this back in and try to read from t14/10 to ground it was open?

To check the wiring continuity you can check backwards from this two pin connector to the T-14 connector - one side should be grounded and the other should go to t14/10.

Click to expand...

Finally had a chance to get under the car and double check this. There is continuity between one side of the pin and t14/10, and the ground on the other side was good. Looks like the clutch coil resistance isn't ok, seems the circuit is open. So looks like there are two problems. No power at the two-pin connector and an open circuit across the clutch coil. I took it to a mechanic and he confirmed this was the case (he unsuccessfully tried jumping the compressor, and noted there was no voltage going to the plug at the compressor).

Two questions: I assume this means the whole compressor needs replaced, or is it possible to replace the clutch coil? Any thoughts on the separate issue of no voltage going to the compressor? Perhaps a bad FCM?

Many people have simply replaced the clutch with either a new one or used one.

Have you been through the troubleshooting guide in post #1 for the AC system?

Yeah, everything seems to check out. I see at the very end it says if I'm still not getting voltage then it is a bad fan control module. Thanks for all your help!

Hi folks, this is my first time on the site. My ac quit working the other day. Everything was fine and then all of a sudden it started blowing hot air. I looked and the compressor clutch doesn't engage anymore. I checked the pressures and they're fine. I checked the fans for low speed operation when the ac turns on and they work fine. I unplugged the compressor and checked for twelve volts with a test light and it only flashes once every four seconds on pin 1. I also checked the compressor coil for resistance and it's infinite. I just can't make any sense of it. It's like the compressor gets juice for a quick second and then something shuts it off real quick. Any suggestions? Thanks

If the compressor coil has infinite resistance, then it is bad. It should be 4 ohms or so.

I would verify that even when I put 12 volts on the coil, it does not engage - just to verify what you read with your meter.

Load the circuit with a resistor of about 4 to 10 ohms (or a good clutch coil) and then check the voltage on the loaded circuit. There are active components in the circuit trying to maintain voltage at about 9.5 volts or so. Perhaps the resistance of your test light is such that the circuit cannot work properly.

Another TDI dead A/C (clutch not engaging) .... made it to section A - #2 .... no voltage on pin t10b/5.

Moving to Section B > fuse 25 is good, and I have 12v at fuse panel.

If I pull the connector off F129, the condenser fans go off, so I'm assuming (maybe wrong) that switch to be good.

I have about 90psi on both sides of gauges with A/C off so I'm assuming that's within spec at least to engage clutch.

That brings me to F38 the Ambient Temp Switch, which I can't find. It's supposed to be behind d/s headlight, but I don't see it.

Also, F163 doesn't appear to be where the manual says it is. There are three coolant looking switches together at the rear of head. Is one of them F163?

Can someone point me in the right direction?

Thanks,
Mike

I think you are in the wrong troubleshooting section.
Your car was almost certainly built after 5/99 and so it does not have an F129 (4 wires), it has a G65 (3 wires) in the same place. You can read your month of manufacture on the placard in the driver's door.
Your car's ambient temperature sensor is under the windshield plenum. Remove the wipers, remove the black plastic grill, you should see it near the left side of the car.

Have you measured your clutch coil resistance? It should be about 3.8 ohms or so.

Thanks Dan,

Strange, I got in the car this morning to go to church, the A/C is working again.....go figure.

I must have jiggled some wires or something....I have no idea.

Mike

Alright, I will try to make this as short, but as detailed as possible. This past Thursday/Friday morning AC worked fine. On way home from work (105 F outside) I noticed the AC was not working. Went to the internet, found this post and did the following:
- Key on, AC on, Fan Speed 1 - PS Fan Fine; DS Fan No Spin
- Same as above but gave DS fan a "push" and it rotated but not well
- Tried blowing compressed air in the motor per one of the posts but no change

So now my question is the following; I have read through the troubleshooting guide and the fan repair guide, but it seems to me that since PS runs and the DS doesn't that the motor on the DS needs to be fixed. Is this right or do I still need to go through the different jumpers/checks as well?

If this is correct I plan on removing and attempting to repair the fan tonight after I get off work. Just in case the repair doesn't work are there any suggestions as to where to buy a replacement motor?

I appreciate any tips I can get.

For the fans, just go ahead and fix the one that does not turn.

One fan not turning would not totally disable the system. It might not run quite as cool, but it would run.

Is your AC compressor clutch latching?

You are correct, the system was still running and the air was marginally cool but after I got off the interstate and started driving in the city it was noticably hotter. I think the ambient air temp for the day was around 112 and with humidity I know it felt hotter. I did check it while driving that afternoon by turning the AC off and then on and it did get hotter when off and cooler when I turned it back on so I assumed that the clutch/compressor was still running fine. I will try and tear the motor out this evening and clean up the brushes as noted. 6.5 years isn't bad especially considering I run it 360 (+/-5) days a year.

Thanks alot for this post, you have easily saved TDIers thousands of dollars.

Alright, I have pulled the fan/motor and removed the back cover plate and pulled out the brush plate per the instructions. Unfortunately the pic shows what my brush holders look like and to me they look alot like the ones in your repair guide. So do you think these are repairable or will I need to replace the brush holder. Also in the repair guide you mentioned that all you needed were some spare parts to make that one working and I wanted to see if you could point me in the right direction.

https://picasaweb.google.com/lh/photo/YdgfhSUh4_GXovcmreQPDQ?feat=directlink

Thanks

I had a spare fan laying around with another problem. So I robbed from it. I do not know of a source to buy spare parts.