Fans run on slow for 5 mins after shutdown - new controller

MikeS_18

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Feb 18, 2005
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Bow, NH
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'03 Jetta Wagon, '13 Passat SE, '64 Ford Econoline
2003 Jetta 5 spd. I was having wacky performance with my fans for a while - they'd come on at weird times, would not shut down etc but my AC was inoperable so I unplugged them and didn't care.

I started to work on my AC this August and while having the front off, I replaced the fan controller with a new one from IDParts. I now have an issue with the AC clutch not engaging and not getting 12V to the compressor but a side issue is this:

Whenever I turn the car off, the fans run on slow speed for ~5 minutes even if the temp outside is 50 degrees. Again, it's a new controller and the behavior is not wacky but rather consistently running for about 5 mins after shutting engine off.

Ideas?
 

vtpsd

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Vermont
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03 jsw TDI, audi 90 AHU swap
I have the same issue with the fans. I havent had time to investigate, I just pulled the fuse. I rarely need the fans in Vermont.

I kind of assume the temperature sensor that is calling the fans on is bad. Probably not too bad to test.
 

oilhammer

Certified Volkswagen Nut & Vendor
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outside St Louis, MO
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There are just too many to list....
Your statement about the A/C is confusing. You said your A/C did not work... so what was the diagnosis there when you started to work on it? If your A/C didn't work with the old controller, then how would you know if the clutch not engaging is a new problem or not?

I would want to verify that the fans *can* work via the temp switch in the radiator first, even though it is rare the ALH ever requires this. This is easy, takes a double male ended spade jumper wire and ~2 minutes once the side shield is off. Unplug the sensor on the radiator, and with the key ON, jump the wires.... there are three (you cannot short anything), just jump two for low speed, then another two for high speed (I forget the colors).

That will at least tell us the fans both work on both speeds. Report back with what you find. You may have just had a bad temp sensor in the radiator originally causing the fans to run longer than they should have.
 

gforce1108

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A blown fuse 16 will cause the fans to run after the car is shut off. I can't remember what else that feeds though.
 

AndyBees

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Southeast Kentucky
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Silver 2003 Jetta TDI, Silver 2000 Jetta TDI (sold), '84 Vanagon with '02 ALH engine
Well, I've studied the Fan Control Module (FCM) electric schematics and associated circuits numerous times and cannot determine why a blown #16 Fuse will cause the two Fans out front to run on. It has to be something internal of the FCM that allows this phenomenon to occur. I've never seen this but have read about it in a few Threads. I guess pulling that fuse would be an easy test.

Fuse 16 gets its power from connection 501 (always hot). There is nothing else down stream from Fuse 16 other than the FCM. The circuit connects through Pin T14/4of the FCM with a 1.0mm wire. Pin T14/10 on the FCM connects to a 1.0mm wire that goes to the AC clutch with no other function. So, again, it must be something internal of the FCM that causes the two Fans out front to continue to run when Fuse 16 is blown.

But, the OP says his two fans run for about 5 minutes after the engine is shut-down.

As already suggested, I believe the problem is with the Radiator Thermo Switch (RTS).

Other than the AC system circuits and the RTS, there is no other circuit that provides current to those fans.

The info below is of a trivial nature only to the OPs problems ...just me jabbering.:D

Fan operation by the Radiator Thermo Switch (RTS)
The Low Speed circuit (2.5mm wire) from the RTS goes directly to the fans.
The High Speed circuit (1.0mm wire) goes to FCM. Thus, out of the FCM at T4a/4 is a big 6.0mm wire that splits to two 4.0mm wires to each Fan for high speed.
Summary, the Fans are operated on low speed directly through the RTS and on high speed indirectly through the FCM.

Fan operation by the AC system
The Low Speed circuit (2.5mm wire) comes from the FCM at T4a/2.
The High Speed circuit is the same one as described above.

So, I believe that the AC only turns on the Low Speed. High Speed only comes into play when the RTS demands more cooling due to hotter coolant flow*. Rationale, there is no sensor in the AC system that monitors temperature anywhere that would demand High Speed on the two fans.

*However, since there are two circuits in the AC system, that go to the ECU, the ECU may be responsible for high speed during AC operation. Or, monitoring engine temp, the ECU may cut-out the AC during an over heat situation ...... dunno .. maybe more experienced guru can chime in.
 

oilhammer

Certified Volkswagen Nut & Vendor
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outside St Louis, MO
TDI
There are just too many to list....
The ECU always has an override option for clutch engagement. Coolant overtemp (via the green CTS), full load demand (when you plant your right foot down), idle drops too low (like you flubbed the clutch on take off... hard to do on an ALH, but possible).

The fan controller uses two inputs, the temp sensor on the radiator, and the refrigerant pressure switch on the A/C high side line near the expansion valve. Either of those can cause the fans to come on, but the refrigerant sensor is only for high speed request, as the fans run on low ANY time the A/C is switched on.
 

AndyBees

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Silver 2003 Jetta TDI, Silver 2000 Jetta TDI (sold), '84 Vanagon with '02 ALH engine
Thanks Oilhammer ....

So, the high pressure switch kicks-off the AC Clutch if pressure is too high. Considering there would be lots of heat involved, you'd have to assume that the Fans would continue to blow. Right?

Also, there is one other input, ambient air temp sensor. If too cold out, no AC function. Or, if a critter chews the wires on that sensor, no AC either (happened to my 2000 Jetta).

Back in late July, I installed a new/used AC compressor on a Jetta. After vacuum completed, started the engine and turned on the AC and fans come on. While charging, the compressor kicked-in and then off... did that a couple of times real close together and then stayed on. So, question is, does the pressure switch also monitor low pressure?? Or, was the plug connector at the AC compressor just not making good contact? I never gave that a thought at the time....... just charged it up and away it went doing it's thing.
 

oilhammer

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outside St Louis, MO
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There are just too many to list....
The pressure sensor does both. Low inhibit (as in if there was no refrigerant) and high which kicks the fans on high, then if necessary high side inhibit.

Remember, and this is important, the G65 is a SENSOR, not a switch. ;)

3 wires, power, ground, then signal to the ECU, which in turn sends data to the fan controller.
 

MikeS_18

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'03 Jetta Wagon, '13 Passat SE, '64 Ford Econoline
Let me add more color on my situation before I read all those helpful responses.

I had a leak in the condenser. I replaced that and did the fan controller while I had the front end off. I charged the AC system and the compressor clutch did not engage.

Tested the magnet and it was bad - replaced the magnet.

Compressor still did not engage. Charge was holding after 2+ weeks so I have pressure in the system.

Pulled the connector to the compressor and I am only getting 5-6V on that wire. Not sure what's up with that but waiting on Nuts&Bolts (Rich T) to help debug that one. Going to put direct 12V on that wire just to see if clutch engages.

Meanwhile, this fan issue so I thought I'd ask on that one.
I'll check fuse #16.
 
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oilhammer

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outside St Louis, MO
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There are just too many to list....
The clutch gets a voltage "spike" that settles back to around 7v IIRC. It takes less current to hold the clutch engage than it does to get it to engage initially.
 

MikeS_18

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Does replacing the pressure sensor require the system to be evacuated?
 

AndyBees

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Silver 2003 Jetta TDI, Silver 2000 Jetta TDI (sold), '84 Vanagon with '02 ALH engine
If the AC clutch wasn't operating, how did you charge the system? I've never been able to get a whole can in even with a deep vacuum without the compressor pulling it in.

Seems I read somewhere that the Sensor can be changed without evacuating the system.

Changing the AC High Pressure Sensor on an MKIV

https://www.youtube.com/watch?v=uptAtVhWiFc
 
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AndyBees

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Silver 2003 Jetta TDI, Silver 2000 Jetta TDI (sold), '84 Vanagon with '02 ALH engine
You need to invest in a set manifold gauges.

Without the AC compressor being in operation, the pressure will be the same on both the high and low side. A set of manifold gauges will show you what you need to know about your system.
 

oilhammer

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outside St Louis, MO
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There are just too many to list....
If the AC clutch wasn't operating, how did you charge the system? I've never been able to get a whole can in even with a deep vacuum without the compressor pulling it in.

Seems I read somewhere that the Sensor can be changed without evacuating the system.

Changing the AC High Pressure Sensor on an MKIV

https://www.youtube.com/watch?v=uptAtVhWiFc
I charge cars up every day with a machine no problem, never an issue, never need to start the car. How do you think they do it at the factory? :p
 

AndyBees

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Silver 2003 Jetta TDI, Silver 2000 Jetta TDI (sold), '84 Vanagon with '02 ALH engine
Actually, I had never given it any thought as to how the factory charged the AC system. But considering the manufacturing processes, sure, I can imagine charging the AC system to be a very automated procedure.

Well, I was under the impression that the OP did the re-charge himself, especially when he referenced having pressure on the low side and no mention of the high side! Hmm.
 

MikeS_18

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The OP's ASE certified TDI guru (nutsnbolts) did the low side charge. I simply can't remember what the high side said.

I swapped out fuse 16, no change in the 5 min fan run after engine shut off. Curious.

Still need to do Oilhammer's sensor test. Tomorrow.
 

KyleMillione

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Yaphank, New York
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02 Jetta, 03 Jetta
As for that voltage issue on the ac clutch, there’s a 4 wire flat connector under the battery, attached over the starter, that corrodes. I’d check there if all the wires are connected still. Mine weren’t and I had a alternator light no one could figure out. 2 wires are for the alternator and 2 are for the AC if I remember properly.
 
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MikeS_18

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'03 Jetta Wagon, '13 Passat SE, '64 Ford Econoline
As for that voltage issue on the ac clutch, there’s a 4 wire flat connector under the battery, attached over the starter, that corrodes. I’d check there if all the wires are connected still. Mine weren’t and I had a alternator light no one could figure out. 2 wires are for the alternator and 2 are for the AC if I remember properly.
Thanks! odd behavior certainly can be explained by corroded wiring. I'll check it out
 

runonbeer

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'00 Golf 02M, '10 Golf 02E, '02 UTE 02M
You have a clutch coil that ohms ok and 6v supplied but it’s not engaging?

Have you downloaded and printed off Dan’s truly great AC troubleshooting guide?
 
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MikeS_18

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'03 Jetta Wagon, '13 Passat SE, '64 Ford Econoline
So I spent the morning with Rich (nutsnbolts) and found that I fubared the electromagnet install and it let loose, broke it's wiring and was rattling around under the belt wheel. dumbass, but at least it wasn't something rattling around in the engine making that God awful noise. Ordered a new one and will let Rich install it.

Now back to the fans - turn the key ON and OFF and they start running on high for 10 minutes - almost exactly ten minutes.

Remove fuse 8 on top of the battery and they stop. Put fuse back and they stay off until you turn the key to ON again. Checked ECM and it says engine temp was 90F so it wasn't thinking it was so hot as to turn on fans. Check coolant sensor on block and on radiator and both had normal operation. Checked high side AC sensor and normal operation.

Stumped Rich (nuts&bolts) and I was no help. So we're wondering if the new fan controller is bad out of the box. Bought this product: https://www.idparts.com/fan-control-relay-module-a4-late-p-1819.html. I hope not. I'll be swapping in my old sketchy one to see if the behavior changes. This ten minute consistent run cycle is really curious.

Any new ideas?
 
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ToxicDoc

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Mar 1, 2018
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Virginia, US
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2001 Jetta, S7, .216
Fuse 16 powers the AC coil I believe and when the fuse is blow the fan stays on. Maybe some type of feedback to your controller from your coil?
 

MikeS_18

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Feb 18, 2005
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Bow, NH
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'03 Jetta Wagon, '13 Passat SE, '64 Ford Econoline
Checked/swapped fuse 16.

Replaced new fan control unit with old sketchy control unit - exact same results. Runs 10mins, give or take, when key is switched on. (sketchy FCU was initially replaced because fans would run intermittently for no reason)

Now we're really stumped.
 
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