Check your radiator/condenser fan operation NOW

My engine started to run hotter than normal (until I turned on the heat full blast and even then it ran hot) and this thread helped me discover that only one fan was running - the one that runs when the AC is on. Thank you!

Both fans should always run or be off together - there should never be only one fan running.

You are welcome.

But I think you will find that you have a stuck thermostat. One fan is more than enough to remove the engine heat from our cars - but it is very marginal for the AC.

Just replaced the large fan on my 02 Golf at 218k miles slow speed was inop. Checked the other mk4's (05 TDI 217k and 03 2.slow 160k) which were both fine.
Thanks for all the info in here, made diagnosis and replacement pretty easy.

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ejallison1 said:

Decided to go with IDParts. Hopefully they have done the research and their TYC brand will hold up. Thanks.

Click to expand...

I had a tyc last about a week. It came from orilley auto parts. Luckily when I went back in and they ordered my replacement I got a VDO, which is made by continental. No issues since.

The Dorman I got at Advance died within a week but the second one (swap at the counter) has been in the car now for four years and is still fine.

DanG144 said:

I think you will find that you have a stuck thermostat. One fan is more than enough to remove the engine heat from our cars - but it is very marginal for the AC.

Click to expand...

So if I run my AC while driving the car to the shop (I can't muster the courage to try to tackle this problem myself - I know very little about repair), it should cool it sufficiently for the trip?

What are the odds that it could be the fuse ... or would neither fan run in that case?

One fuse runs both fans in slow, another fuse runs both fans in fast.

It could still be a bad connection or broken wire.

It will not cause damage running the AC and the car with one fan - it just prematurely ages the components (mainly compressor and RCV) in your AC system due to high temperatures. You might figure it ages a year for each week run with one fan in summer temps and stop and go traffic.

About the stuck thermostat. Check your fluid level before you start. Keep your windows down, AC on, and heat on full, cabin fan on fast, and your car should make it to the shop Ok. If you see the temperature gauge go to 200, shut the car off and let it cool for a while. When it reads 200 it is actually 236F - overheated. When it first leaves 190 going up, you are already at 226F - because the gauge is controlled by the computer it stays reading 190 from about 167 to about 226.

DanG144 said:

When it reads 200 it is actually 236F - overheated. When it first leaves 190 going up, you are already at 226F

Click to expand...

Interesting, and good to know. That explains why it stayed at 190° unless I was on the highway or going up hill. I found that strange. Also, coolant levels are good - is there another fluid that could be low that I should be looking for? Of course, I check oil on a regular basis.

I just meant to check the coolant reservoir level.

DanG144 said:

I just meant to check the coolant reservoir level.

Click to expand...

Oh yes, that was the first thing I checked, all is well there. Thank you for your help.

Looks like I need a replacement for the right side fan on my other '03 Wagon. Do the gasser MKIV Jettas use the same fan? (Partsgeek.com has a Febi-Bilstein for $84.48 but does not allow you to search specifically by engine. This one says OK for 1.8L, 1.9L, and 2.0L and I assume the 1.9L is the tdi.)

The one's I have seen were all the same, for gassers and diesels.

Check RM European I bought a Febi there for about $50

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The AC on my wife's 2003 ALH Jetta GL TDI quit working today. She said it worked at the beginning of the day and then just quit.

I tried to trouble shoot it, checking the fuses, but they are fine. I checked the coolant pressure and it's good.

I don't hear the AC compressor kick on, and I can't really see it without getting under the car for a better look.

The larger, driver side, fan does not spin at all whether I have the AC turned on or not.

The smaller fan spins when I turn the AC on and when the AC is off and I let the engine get warm. So, it seems to be doing all of the work to cool the engine and the condenser.

So, since the AC compressor doesn't come on and the big fan doesn't come on, what might be the cause?

First guess - over pressure and temperature from failure of the large fan. Possible it blew out Freon because of this, or just ran the components too hot and they failed.

Obviously fix the fans (double check you have low and high speeds from little fan). Second, I just had a Golf that pressures looked perfect - and I recovered 81 grams from it.

2003 probably has the pressure sensor G65 instead of pressure switch. Diagnosis of that thing is easier with a known good part (Bought one for my tool box) than to wire up and read the sensor. But with a large fan not working and sudden stop of AC, I'm leaning towards check for Freon charge (and possible loss). If it blew out then time for compressor, because once the safety valve blows, it never holds properly again.

Let us know what you find,

Jason

The pressure did read high, but I didn't think much of it. What is the best way to relieve the pressure?

if my compressor clutch doesn't engage at all and only my passenger side fan works, is there anyway that my compressor doesn't need replacing?

i've got to replace the driver fan first, ik.

benIV said:

if my compressor clutch doesn't engage at all and only my passenger side fan works, is there anyway that my compressor doesn't need replacing?

i've got to replace the driver fan first, ik.

Click to expand...

Did you read thru page 1 of this thread? Should certainly help with the fan.

yeah i went through it and have it ready to go. I was going to do the fan today but it's been raining. so maybe later this evening.

I'm still a bit confused with the compressor.

I got the impression that as long as my pressure was good and at least one fan was working, the compressor would at least engage. Since it isn't engaging at all, I have a feeling the clutch at least is shot. I guess I'm just having issues trying to determine how best to troubleshoot the compressor.

I only commented because having followed this thread some, it seems like Dan has addressed every condition of failure. It's a lot to go thru. He may yet offer comment on your post, he's been very patient and helpful.

oh i understand. he has been amazing with what he's done. it's been difficult to get through all 1700 or so posts, but i'm chugging through. lol.

I think I was missing a section when I was trying to quickly browse through some of the pdfs. I went through and reread some of the pdfs from Dan more closely and found the air conditioner control circuit issues. I think my next step should be to run the tests he describes on the G65 and then the FCM and the J293.

Part of me just wants to replace the compressor, but I'd hate to put a new one in and have the same issue because i was lazy.

The amount of work Dan and everyone has done with this thread is fantastic and i'm super grateful. You all have done some amazing work!

I relieved the pressure so it's back down to normal. The AC compressor still did not kick on. I ordered a new aftermarket fan from idparts.com that will be here sometime early next week.

Been troubleshooting my failed AC system on 2002 Golf TDI. Just thought I'd write up a report at this point... still not fixed.

When I started troubleshooting I found one of the fans was not working, so I probably had an overpressure at some point. replaced the fan. I work at a community college so I'm fortunate to have access to the automotive class to check pressures, vacuum, leak test and refill the system. I determined the compressor was not functioning. replaced it and they refilled the system and it worked for a week or two, though with some random irregularities, like no compressor engagement driving to the store and then it works fine going home. Then it stopped completely and winter came so i was less motivated. Spring arrives and I revisit the issue. Automotive class finds I have no r134a and it has leaked out of the G65 sensor. replace that. Still no compressor engaging and now the fans do not run when AC is on. troubleshooting fan circuits and FCM per Dan's excellently documented procedure. low speed fine when testing from radiator thermoswitch, but no high speed. Check fans themselves and they do have both speeds working fine. I see lots of cheap counterfeit FCMs on ebay for $20 and real OEM ones for $100. I roll the dice and spring $30 for a used one. Now signals from radiator thermorswitch operate fans properly. Incidentally, I think the low speed is switched on directly from the radiator thermoswitch, but the high speed is operated by the relays in the FCM. But still, my AC compressor is not getting the signal to engage. I'm wondering if the R134a has all leaked out again. I noticed an odor coming from the vents for a while since it was last charged after the leaking G65 was replaced, while I was waiting for the FCM to arrive. It smelled a little like hot or burning electrical insulation. sound familiar?

So now I had a (better) working FCM and decided to hack my old one open. I found some residue on the circuit board. possibly water got in it? I cleaned the board and reflowed a couple solder joints that looked dull in color. I hooked my FCM back up and now it was working! At least as far as the tests you do from the radiator thermoswitch connector. Below are some before and after photos, I hope.

I'm going to have the auto guys check to see if it's leaked out again and try to determine where it's leaking now, if so.

https://goo.gl/photos/K5vqAps1asu5rab37

https://goo.gl/photos/UWTWutS3fXa31nhS8

Thanks,
Edward

Hey Edward. Where in NC?

as for your problem, if you're leaking still and you smell something in the cabin, perhaps there is a leak in your evaporator? I'm not sure this would make sense or not. And then IIRC, too low a pressure will keep the fans from running in slow mode. compressor might even not run if pressure is too low?

jiveabillion said:

The pressure did read high, but I didn't think much of it. What is the best way to relieve the pressure?

Click to expand...

NOOO! The high pressure is not stopping it from working. What I was saying is you lost Freon from the system and there is not enough in there for the compressor to turn on. It only takes a small percentage (say 10-15%) of Freon to cause a pressure rise on a hot day and make it look like a charged system, but a lot of the time the compressor will not turn on.

Most likely the system "over heated" because of the large fan not working and the safety pressure relief valve on the compressor vented Freon until the pressure dropped back to safe levels. After it vents enough Freon the system won't turn on, even though the pressure looks ok. Bad part is once you trigger that safety valve, you have to replace the compressor.

First replace the large fan. Second make sure the small fan works high AND low speeds. Third, evacuate and recharge the system. From there you can see if it will work. Possible, but you will probably loose Freon through that safety vent.

Jason

Hey all! First off, huge thanks to everyone here, especially Dan for all this excellent information. I've been tracking down an A/C issue for 7 years, and all this info has been incredibly helpful over the years. Sadly, I haven't been able to get it going. I'm a gasser, hopefully you all don't mind. 2003 Jetta Wolfsburg 1.8T. A/C died 7 years ago, I was told I needed a new compressor, couldn't afford it, waited a few years, replaced it, still no go. At this point nearly every component has been replaced, some components up to 4 times. Here's what I've got:

Key on, A/C on, cabin fan speed selected - no fans, no A/C

Jumper through the thermoswitch - can get both fans to run in both slow and fast speed

T4a connector:

pin 1 - 12v
pin 2 - continuity to ground. 20ohm resistance with key off, 330ohms with key on
pin 3 - 12v
pin 4 - continuity to ground. 20ohm resistance with key off, 326ohms with key on

T14 connector:

pin 1 - Irrelevant - 1.8T doesn't have after-run coolant pump
pin 2 - continuity to middle wire high pressure switch - 30% duty cycle
pin 3 - got 12v as recently as a week ago, today reads 56.6mV
pin 4 - 12v
pin 5 - continuity to wiring harness for ambient temp switch in rain tray. Duty cycle between pin 5 and pin 14 (unplugged) jumps around, but is around 6%. Was 87 degrees approximately today.
pin 6 - continuity to ground. 20ohm resistance with key off, 316ohms with key on
pin 7 - continuity to fan thermal switch
pin 8 - 12v when A/C switch is on
pin 9 - 12v when ignition on
pin 10 - continuity to A/C clutch - clutch will engage if you jumper here
(as an aside, I have seen the compressor spin when 12v is applied)
pin 11 - irrelevant as not a diesel
pin 12 - blank
pin 13 - 11.5v reference voltage, but does jump around a lot
pin 14 - continuity to wiring harness for ambient temp switch in rain tray
(as an aside, Bentley and this write-up say you can read pins 5 and 14 for continuity. I have never seen continuity between these two, and I've gone through 3 ambient temp switches. But I can read from them, as I mentioned, 6% duty cycle but jumps around)

I have 8ohms resistance through the driver side fan
14.5ohms resistance through passenger side fan

Resistance from T4a-2 and T4a-4 and T14-6 to the battery negative terminal is 0.1ohms, but when battery is connected, readings are as I mentioned above, 20ohms key off, around 320 key on.

Resistance on the compressor clutch is 5ohms

I have gone through 4 different FCMs, but I can't prove for sure that any of them work, I didn't pull them directly from a known good A/C system and put them immediately into my car.

I think that covers everything I've learned so far, but if you ask, I can dig up the information, I've been keeping pretty decent records.

I know I need to get the fans working first, but I am running out of ideas on what to do next. Help?

smomarkiv said:

Hey all! First off, huge thanks to everyone here, especially Dan for all this excellent information. I've been tracking down an A/C issue for 7 years, and all this info has been incredibly helpful over the years. Sadly, I haven't been able to get it going. I'm a gasser, hopefully you all don't mind. 2003 Jetta Wolfsburg 1.8T. A/C died 7 years ago, I was told I needed a new compressor, couldn't afford it, waited a few years, replaced it, still no go. At this point nearly every component has been replaced, some components up to 4 times. Here's what I've got:
Key on, A/C on, cabin fan speed selected - no fans, no A/C

Click to expand...

Ah, there is first problem. Even in 2003 I believe radiator fans will come on with key on, engine not running, AC switch on and blower fan on. Sounds like there is a reason code for why AC is not working in ECM MVB 50ish.

smomarkiv said:

Jumper through the thermoswitch - can get both fans to run in both slow and fast speed
T4a connector:
pin 1 - 12v

Click to expand...

Fuse S164 on the battery

smomarkiv said:

pin 2 - continuity to ground. 20ohm resistance with key off, 330ohms with key on

Click to expand...

This is radiator fan low speed and should show continuity to thermo switch pin 1 and both radiator fans pin 2

smomarkiv said:

pin 3 - 12v

Click to expand...

Fuse S180 on battery and shares power to thermo switch pin 2

smomarkiv said:

pin 4 - continuity to ground. 20ohm resistance with key off, 326ohms with key on

Click to expand...

This is radiator fan high speed and should show continuity to both fans pin 1, nothing else.

smomarkiv said:

T14 connector:
pin 1 - Irrelevant - 1.8T doesn't have after-run coolant pump

Click to expand...

BUZZZ! Wrong! I drive one and can verify 1.8T has after run coolant pump. Just about always bolted to fan shroud in front of alternator.

smomarkiv said:

pin 2 - continuity to middle wire high pressure switch - 30% duty cycle
pin 3 - got 12v as recently as a week ago, today reads 56.6mV

Click to expand...

Lucky - this is a communication wire to ECM and TCM (if automatic)

smomarkiv said:

pin 4 - 12v

Click to expand...

Fuse S16 10a

smomarkiv said:

pin 5 - continuity to wiring harness for ambient temp switch in rain tray. Duty cycle between pin 5 and pin 14 (unplugged) jumps around, but is around 6%. Was 87 degrees approximately today.

Click to expand...

Huh? see below.

smomarkiv said:

pin 6 - continuity to ground. 20ohm resistance with key off, 316ohms with key on

Click to expand...

This is ground circuit for G65 AC pressure sensor, N25 AC clutch, and both radiator fans. Ground terminates "engine compartment left". Probably under the battery. Resistance is way too high for a straight run to ground. See note below about resistance measurements.

smomarkiv said:

pin 7 - continuity to fan thermal switch
pin 8 - 12v when A/C switch is on

Click to expand...

12V from E35 AC switch - comes through blower fan and resistor pack.

smomarkiv said:

pin 9 - 12v when ignition on

Click to expand...

12v from Fuse S5

smomarkiv said:

pin 10 - continuity to A/C clutch - clutch will engage if you jumper here
(as an aside, I have seen the compressor spin when 12v is applied)
pin 11 - irrelevant as not a diesel
pin 12 - blank
pin 13 - 11.5v reference voltage, but does jump around a lot

Click to expand...

This is the communication wire to cluster.

smomarkiv said:

pin 14 - continuity to wiring harness for ambient temp switch in rain tray
(as an aside, Bentley and this write-up say you can read pins 5 and 14 for continuity. I have never seen continuity between these two, and I've gone through 3 ambient temp switches. But I can read from them, as I mentioned, 6% duty cycle but jumps around)

Click to expand...

What the heck are we doing reading duty cycle at a thermo switch? Disconnect the J293 FCM and the ambient temperature switch. Jump the terminals at the ambient temp switch with a paper clip, read the resistance at T14 between 5 and 14. Read ohms on the ambient temp switch, toss in freezer for a while and recheck.

smomarkiv said:

I have 8ohms resistance through the driver side fan
14.5ohms resistance through passenger side fan
Resistance from T4a-2 and T4a-4 and T14-6 to the battery negative terminal is 0.1ohms, but when battery is connected, readings are as I mentioned above, 20ohms key off, around 320 key on.
Resistance on the compressor clutch is 5ohms
I have gone through 4 different FCMs, but I can't prove for sure that any of them work, I didn't pull them directly from a known good A/C system and put them immediately into my car.
I think that covers everything I've learned so far, but if you ask, I can dig up the information, I've been keeping pretty decent records.
I know I need to get the fans working first, but I am running out of ideas on what to do next. Help?

Click to expand...

Just a note on resistance measurements - they are performed on an ISOLATED circuit with no power applied. Checking resistance to ground or a sensor is done with everything else on that circuit disconnected, or you will read resistance base on the sum of the circuits. If a ground is shared then you will read resistance through EVERYTHING that shares that ground.
This is why I do voltage drops - I can read the resistance in a live circuit. Some resistance problems only show up under load.

I'm reading a wiring diagram as I read your post and type answers - I looks like there is open or partially open ground between FCM and ground under battery. Easiest would be to take the battery out and clean all the grounds right there.

Jason

Hey, thanks for the quick response!

Yes, there is definitely a reason that the fans and A/C clutch are not coming on when the key is on and the A/C switch is on, that's what I'm trying to figure out. I've dug around in it with VAG-COM, but there are no information blocks for HVAC for a MkIV with manual A/C, so I really can't get any answers there. I'll get someone to run it again and look around MVB 50, but I have yet to see anything related to HVAC in there.

I'm not sure what to say about the after-run coolant pump, I have the Bentley and several wiring diagrams of the A/C system, they specifically say that the after-run coolant pump is the 2.8 only. I'm not home but I'm happy to snap pics of those diagrams later.

Cleaning out the grounds under the battery tray is actually the most recent thing I've done. Unbolted, sprayed with contact cleaner, wire brushed, cleaned posts to bare metal, reassembled with dielectric grease. Resistance between each one of those grounds and the negative terminal of the battery is 0.1ohms, perfect. Doesn't seem to be an open ground anywhere in that circuit. But I find it strange how high the resistance jumps when I key on. I'm far from an electrical expert, I'm hoping someone more knowledgeable can clue me in on if this is an issue or not.

I can check resistance on the ambient temp switch later and report back. This is the third one I've put it, so while all three could be bad, I have a hard time believing that is the issue. But at this point I'll believe anything.

SilverGhost said:

Ah, there is first problem. Even in 2003 I believe radiator fans will come on with key on, engine not running, AC switch on and blower fan on. Sounds like there is a reason code for why AC is not working in ECM MVB 50ish.
Fuse S164 on the battery
This is radiator fan low speed and should show continuity to thermo switch pin 1 and both radiator fans pin 2
Fuse S180 on battery and shares power to thermo switch pin 2
This is radiator fan high speed and should show continuity to both fans pin 1, nothing else.
BUZZZ! Wrong! I drive one and can verify 1.8T has after run coolant pump. Just about always bolted to fan shroud in front of alternator.
Lucky - this is a communication wire to ECM and TCM (if automatic)
Fuse S16 10a
Huh? see below.
This is ground circuit for G65 AC pressure sensor, N25 AC clutch, and both radiator fans. Ground terminates "engine compartment left". Probably under the battery. Resistance is way too high for a straight run to ground. See note below about resistance measurements.
12V from E35 AC switch - comes through blower fan and resistor pack.
12v from Fuse S5
This is the communication wire to cluster.
What the heck are we doing reading duty cycle at a thermo switch? Disconnect the J293 FCM and the ambient temperature switch. Jump the terminals at the ambient temp switch with a paper clip, read the resistance at T14 between 5 and 14. Read ohms on the ambient temp switch, toss in freezer for a while and recheck.
Just a note on resistance measurements - they are performed on an ISOLATED circuit with no power applied. Checking resistance to ground or a sensor is done with everything else on that circuit disconnected, or you will read resistance base on the sum of the circuits. If a ground is shared then you will read resistance through EVERYTHING that shares that ground.
This is why I do voltage drops - I can read the resistance in a live circuit. Some resistance problems only show up under load.
I'm reading a wiring diagram as I read your post and type answers - I looks like there is open or partially open ground between FCM and ground under battery. Easiest would be to take the battery out and clean all the grounds right there.
Jason

Click to expand...

Yeah, I was looking at that Bentley wiring diagram as I typed - It has a note saying (VR6) only for the after run coolant pump. I walked out and looked at my 2002 and coworker's 2005 1.8T - both have that pump bolted to the fan shroud.

You need to double check the ground circuit from T14/6. This should be 0.1 ohm to ground. Also you should NOT be checking this with power in the circuit (no key on checking). I suggest you disconnect G65 (AC pressure sensor), N25 (AC clutch), and both fans, then check resistance to ground. From what other people have posted you may find there is a break in the wire near T14 (@FCM) because its under the batter and acid/corrosion.

If you still have a problem, then disconnect the 4 pin plug that should be clipped onto holder on starter. Two of those wires go to AC clutch. Check resistance between T14/6 and that connector. Also check resistance between both radiator fans and T14/6.

If there is still a problem then check between fans and ground, G65 and ground, N25 and ground. If they all check out good (0.1 ohms or about that) then easiest solution may be just bypass that wire by running a new one from T14/6 to ground or to fans ground circuit. But if you peal that harness open, I bet you find the wire near T14/6 is damaged.

Jason

SilverGhost said:

Yeah, I was looking at that Bentley wiring diagram as I typed - It has a note saying (VR6) only for the after run coolant pump. I walked out and looked at my 2002 and coworker's 2005 1.8T - both have that pump bolted to the fan shroud.

You need to double check the ground circuit from T14/6. This should be 0.1 ohm to ground. Also you should NOT be checking this with power in the circuit (no key on checking). I suggest you disconnect G65 (AC pressure sensor), N25 (AC clutch), and both fans, then check resistance to ground. From what other people have posted you may find there is a break in the wire near T14 (@FCM) because its under the batter and acid/corrosion.

If you still have a problem, then disconnect the 4 pin plug that should be clipped onto holder on starter. Two of those wires go to AC clutch. Check resistance between T14/6 and that connector. Also check resistance between both radiator fans and T14/6.

If there is still a problem then check between fans and ground, G65 and ground, N25 and ground. If they all check out good (0.1 ohms or about that) then easiest solution may be just bypass that wire by running a new one from T14/6 to ground or to fans ground circuit. But if you peal that harness open, I bet you find the wire near T14/6 is damaged.

Jason

Click to expand...

Between T14-6 and negative terminal of the battery is 0.1ohms, 20ohms if the battery is fully connected. The rest I'll get out and check in the next couple days, including checking resistance on the ambient temp sensor. Work has been keeping me busy, but I'll check all that Sunday, probably. Thanks!

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