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    Thread: Errors in the Wiring Diagrams for A/C Radiator Cooling Fan Harness

    1. Member Legoguy's Avatar
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      05-19-2014 12:00 AM #1
      Hey guys; been a long while since I've posted up in here. Good to see the same familiar faces kicking around.

      I recently purchased a '92 Wolfsburg Edition to eventually replace my rusting-away '88. It has all the fixin's except a power top - this includes A/C.

      The PO of the car decided they would replace the relay socket in the wiring harness for the Radiator Cooling Fan; you know, that one that's up front by the battery, on a bracket attached to the front of the fender. Not all-together a bad idea, but the execution could have been better, they could have used the proper VW part for it, etc. I didn't like it, so I set out to look at "reverting" or correctly replacing that socket with the proper part. But then I remembered... I have an '88 sitting right there, that also used to have A/C. Awesome.

      I pulled out the cooling fan harnesses of both cars for comparison, and immediately noticed one difference.



      The '92 had this extra black 1-pin connector (center of the picture), in the circuit that powers (what I thought to be at the time) the high-speed side of the fan. My first thought was that the mating connector of this was the output from the cooling fan after-run timer control unit thingy, relay 14 according to cabby-info and the Bentley. Fair enough. But what do the Bentley wiring diagrams say?

      Not much... it's connector T1k on this diagram (AC, 1990+), track 8:



      So the wiring diagram mentions it, but doesn't actually specify what it's connected to, just that it's there, located near the left headlight, and has two R/BK wires coming out of the single-pin housing. Okay, so we move on to the 1991+ Main Wiring Diagram, track 46:



      There's T1k again, I'm not sure if the different wiring diagrams share connector numbers, but this looks right. One issue with this is that the main wiring diagram here specifies that T1k is behind the fuse panel. Another is that it specifies a thicker 1.5mm (14 gauge) wire going to it. On the car, I have at most a 16 gauge wire... it's quite small...

      To make matters more confusing, the whole physical wiring harness seems to be backwards. At first glance, it looks like the high-speed side of the fan is powered by the low-temp switch, the low-speed side is powered through the relay that's triggered by the high-temp switch...wait, what's this? The Bentley diagram for A/C above says that two of the wires going to the fan are R/BK? Madness! They are clearly R/W, R/BK, and BR.

      Waaaiit a second... the pin numbers of the fan connector tell the whole story.

      On the fan connector in front of me, you have..
      1. R/W, which corresponds to high speed
      2. R/BK, which corresponds to low speed
      3. BR, Ground


      On the 2-temp radiator coolant temp switch, we have..
      1. R/BK, high temperature switch (105°C)
      2. R/W, low temperature switch (95°C)
      3. R, fused power (fuse 1, 30A)


      Ah, there we go. Well done, VW! You switched the wiring colors for the A/C car's harness, when compared to the non-A/C model. Looks like even your wiring diagram guy didn't catch it, when it came to the radiator fan!

      So it turns out that yes, T1k is in fact the output from the cooling fan after-run timer relay, and yes, the main harness that has the mating connector does have a stupidly small wire size considering the load it takes, and yes, this whole system *does* control the low-speed side as intended.

      Not intuitive at all. The correct wiring diagram should look like this:



      But I think it could have been improved overall if VW kept the wire colors the same to begin with...

      That is all.

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    3. Junior Member
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      07-19-2020 01:22 AM #2
      Thank you. Im installing a Ez wiring kit and adding a underhood relay box, this is great.

    4. Senior Member briano1234's Avatar
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      07-19-2020 12:25 PM #3
      Quote Originally Posted by MARLINKID View Post
      Thank you. Im installing a Ez wiring kit and adding a underhood relay box, this is great.
      You have to use both diagrams, the a/c and the regular one. I have been stymied for a bit, a time or two myself.

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    6. Junior Member
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      07-20-2020 01:59 AM #4
      According to cabby info.com on 1988 to 1993 cabbys the thermo switch engages the low fan speed at a pre determined temp and will run on low. They say that when the ac relay sends a signal that the high speed fan comes on....... never mentioning that regardless of the ac relays signal hi and low speeds should work if the temp is reached. 95c low 105c high

      I feel mislead..

      30 amp power is supplied from fuse 1 to pin 30 of the cooling fan relay.

      30 amp power is piggy backed from cooling fan pin 30 to pin 3 of the thermo switch, supplying the the 95c and 105c switches.

      Once at 95c the low speed switch closes, 30 amp power is sent to the after run control unit then to pin 2 of cooling fan internal resistor giving low speed.

      "Yes once the ac relay is energized voltage is sent to the ac high pressure switch. Once the high pressure switch recognizes high pressure voltage is supplied to pin 86 of the cooling fan relay closing the relay and turning high speed on" BUT BUT BUT the cooling fan relay has power provided from thermo switch pin 1 (105c) to pin 86 also so if the temp reaches 105c the ac signal voltage the the cooling fan relay is irrelevant.

    7. Junior Member
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      07-20-2020 02:13 AM #5
      Being that im installing a relay box under the hood and that the ac relay is just used to send a signal to the high speed relay. Why cant i just wire from scratch and run power from pin 2 on thermo switch to pin 2 on the fan? bypassing the after run....

      both fan speeds are on of the same 30 amp fuse source. low speed has no relay just a resistor inside the fan, high speed relay would be needed still.

      So one relay, one 30 amp fuse, i feel it should work

      FYI the same 30 amp fuse is used on both " fan and ac relay" but the ac relay is only energized to send an alternative signal to the fan relay to turn high speed on for ac.

      the ac relay isnt used to energize the fan.

      MY CAR HAS NO AC ANYMORE LOL. ITS CARB CONVERSION AND REWIRE IN PROGRESS. ALL AFTERMARKET WIRING EZ WIRING. keeping it clean looking and tidy.
      Last edited by MARLINKID; 07-20-2020 at 02:16 AM.

    8. Junior Member
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      07-20-2020 03:14 AM #6
      So i should be sleeping but im hooked...

      if i run just the 95c low speed and 105c high speed switch on one relay i wonder how long the low speed fan will run once the car is shut off in the summer....

      two diagrams above i see tk1 goes to the after run module which looks like a relay of some sort.

      it looks like once 70c temp is reached it energizes the low speed fan, but when you turn the car off the low speed fan will still run until the 95c switch opens because the 95c is still energizing the fan. if 70c opens it doesn't cut power. t1k receives power from the after run 70c and the thermo switch 95c. t1k goes to low speed fan lolol

      I dont mean to sound like a know it all im just talking it out. its how i process. any info will help. will my fan run for 30 minutes if i dont use the after run module because im having to wait for the 95c to open?


      EDIT EDIT I THINK IM TIRED!! LOL THE 95C WILL OPEN BEFORE THE 70C. WAITING FOR THE 70C TO CLOSE WOULD HAVE ME WAITING FOR THE FANS TO TURN OFF! HAHA!! THIS IS FUNNY SO I WILL LEAVE IT HERE.
      Last edited by MARLINKID; 07-20-2020 at 03:23 AM.

    9. Senior Member briano1234's Avatar
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      07-20-2020 07:37 AM #7
      Quote Originally Posted by MARLINKID View Post
      So i should be sleeping but im hooked...

      if i run just the 95c low speed and 105c high speed switch on one relay i wonder how long the low speed fan will run once the car is shut off in the summer....

      two diagrams above i see tk1 goes to the after run module which looks like a relay of some sort.

      it looks like once 70c temp is reached it energizes the low speed fan, but when you turn the car off the low speed fan will still run until the 95c switch opens because the 95c is still energizing the fan. if 70c opens it doesn't cut power. t1k receives power from the after run 70c and the thermo switch 95c. t1k goes to low speed fan lolol

      I dont mean to sound like a know it all im just talking it out. its how i process. any info will help. will my fan run for 30 minutes if i dont use the after run module because im having to wait for the 95c to open?


      EDIT EDIT I THINK IM TIRED!! LOL THE 95C WILL OPEN BEFORE THE 70C. WAITING FOR THE 70C TO CLOSE WOULD HAVE ME WAITING FOR THE FANS TO TURN OFF! HAHA!! THIS IS FUNNY SO I WILL LEAVE IT HERE.
      There are two separate sides of the same circuit controlled by 2 different things.

      The Radiator fan switch is for the radiator fan to turn on or off depending on how hot the coolant is when it is really hot the high side closes and turns it on fast.
      other wise it runs at low speed. It will alway run at high as when the a/c is turned on.
      The after run fan switch controls the fan to run after the car shuts off, it is located on the back side of the valve cover and looks like a big brass nut with one wire on it. It controls the fan to run after your running the car and shut it off, depending on the heat of the engine....Prevents Vapor lock.

    10. Junior Member
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      07-20-2020 06:46 PM #8
      I believe we are on the same page about how the system works

      Is there any reason why I need to include the after run and 70c switch when wiring the car from scratch.
      I have a return fuel line that I'm using with my carb so wouldnt this adress a potential vapor lock issue?

      What I want to do it just run the fan off the 95c and 105c thernoswitch. High speed is relay supplied and low speed is 30 amp fused. Basically the identical vw wiring setup with after run module bypassed.

      30amp fused to fan relay pin 30, thermoswitch power provided from relay pin 30 piggy backed to thermoswitch.

      This would make high speed run with the relay and low speed run off the same 30 amp fuse that powers the fan relay.

      I see no reason why this wouldnt work. I dont think after run is essential.

      That being said NASA thought the oring was good to go....

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      07-21-2020 09:23 AM #9
      Quote Originally Posted by MARLINKID View Post
      That being said NASA was hoping the oring was good to go....
      The switch is for cooling the engine compartment and radiator to prevent the high pressure fuel from vapor lock when the engine is shut off. What do you think would happen with your fuel at low pressure?

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      07-21-2020 08:04 PM #10
      Quote Originally Posted by Butcher View Post
      The switch is for cooling the engine compartment and radiator to prevent the high pressure fuel from vapor lock when the engine is shut off. What do you think would happen with your fuel at low pressure?
      Im lost. isn't there plenty of vehicles without after run that operate safely and dont vapor lock. like mg, any 70s vehicle with carbs?

      i do understand what you mean. boiling point increases with pressure. and im running low pressure.

      do 70s rabbits have aftercool? i feel like i would be okay with just a high and low fan speed setup without aftercool.

      i dont mean to sound rude. thanks for your input do you see what i mean though? is it a need?

    13. Senior Member briano1234's Avatar
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      07-21-2020 09:36 PM #11
      Quote Originally Posted by MARLINKID View Post
      Im lost. isn't there plenty of vehicles without after run that operate safely and dont vapor lock. like mg, any 70s vehicle with carbs?

      i do understand what you mean. boiling point increases with pressure. and im running low pressure.

      do 70s rabbits have aftercool? i feel like i would be okay with just a high and low fan speed setup without aftercool.

      i dont mean to sound rude. thanks for your input do you see what i mean though? is it a need?
      The older rabbits ie: 1981 diesel that I drove, had a 2 speed fan switch. The Radiator was powered from the battery to the Radiator fan switch low temp side, then to the fan.
      The Fan has a separate ground.

      When the Car was running a/c the Fan engaged in high speed via the hotter side of the fan switch and a relay powered by the a/c selection.
      very similar to what is now on the car.

      When you turn the car off, the radiator fan would run till the low temp side opened as it wasn't hot any more. If the temp outside exceeded the 95C threshold the fan would turn on and cool the radiator.... simple and effective, and there was no "After Run circuit" per say.

      A 90's era Cabriolet, does worry about pressures, the FPR (Fuel Pressure Regulator) operates the same as a t-stat with heat, as well as you are more worried about residual pressures. I personally have never had a 90 Vapor lock, but all mine were OEM. There is the cooling fan time control unit labeled
      31 in the fuse panel... pn 191955532A

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      07-22-2020 10:52 AM #12
      Do you need this after run portion of this fan? No. Is there a reason that VW put it in there? Yes. Most manufacturers build a car as cheap as they can so they can make money. They felt that they needed this system so they threw the additional money to make it happen. So yes, you need it.

      Some manufacturers decide to put a turbo in their models. VW did not. So just because one manufacturer decides to do something, does not mean all of them will follow.

      The emissions systems were much different back in the 70's and it's possible that the after run system was helping to reduce the load on the evap portion of that system [the vapor needs to go somewhere and that means, the charcoal canister]. Since the emissions system are more strict in the 90's, it's possible that is another reason why they put in this after run system.

      There are a lot of opinions and many times, there is no right/wrong one. You seem to grasp the idea why they put this after run system in. Do as you wish, but if it was my car, I would invest the time/money to get it working. If I lived in Alaska, maybe I would not but I would wonder why I live there.

      BTW, I'm sorry to hear you owned a MG. I'm puzzled why you would compare a MG to a VW. If you were a pig, a MG is like a house of straw.
      Last edited by Butcher; 07-22-2020 at 10:56 AM.

    15. Junior Member
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      07-22-2020 12:23 PM #13
      Haha no i never owned a MG it just came to mind.

    16. Junior Member
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      07-22-2020 12:29 PM #14
      Thanks for the info. I appreciate it.

    17. Member kamzcab86's Avatar
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      07-28-2020 04:30 PM #15
      Quote Originally Posted by MARLINKID View Post
      do 70s rabbits have aftercool? i feel like i would be okay with just a high and low fan speed setup without aftercool.
      I can tell you this: All VWs have an after-run system; they simply differ in their implementation. The 1980-1987 Cabriolets all came with one-speed fans and no after-run thermoswitch. After engine shutdown, the cooling fan will run based on coolant temperature at the radiator fan switch.

      From 1988 to 1993, VW installed a 2-speed fan and after-run thermoswitch. After engine shutdown, the cooling fan will run based on engine bay temperature at the cylinder head after-run switch.

      If you want to ditch the later, more complicated after-run system, simply wire the car like the 1983-1987 cars.
      Cabby-Info.com -- Your online guide to VW Cabriolets/Rabbit Convertibles
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      07-29-2020 09:43 AM #16
      The early Rabbits/Cabriolets did not have an after-run system.

      The radiator fan came on if the coolant temperature switch was activated. Since this system was wired to circuit 30, so in simple terms, the system is on all the time. If the stagnant coolant gets hot enough to activate the switch, the radiator fan will come one, it's just the way it works and should not be confused with the after-run system on the later models. They could of wired the system to circuit 15, but everyone knows the engine temperature rises when the hot engine is shut off. That would not have been a good idea.

      As under hood temperatures rose and the emissions tests got more strict, I suspect they had to keep these temperatures in check. That is why they added the switch and modified the system they already had vs coming up with something completely new. It's cheaper to modify an existing system vs coming up with a completely new way of accomplishing their goal.

      Don't be confused that they all had an after-run system, because they did not.

      If I was going to rebuild an older car, I would do my best to install the after-run temp switch. It's probably harder to find the parts vs making it work.

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      07-29-2020 11:02 AM #17
      I think the distinction was made adequately that the early cars' fan could come on after the engine was run, just by virtue of having the thermostat wired "hot", i.e., not dependant on the ignition switch being in "on" position. That makes it technically an after run system, although admittedly not in the sense we've come to understand on later cars.

      I want to reassure everyone that keeping things simple causes no harm, based on our experience: we have a 2.0 liter 16V running an early (small) radiator with incorporated overflow tank, no oil cooler, and with the radiator fan's high speed side wired directly to 12V with only the fan thermostat and the circuit's OEM fuse. When we stop the engine, the fan sometimes runs for a bit. Most important to this discussion, the absence of all the additional cooling features that were present on the donor Passat has produced no ill-effects in the 8 years we've been running it this way. Interestingly, hard driving produces enough air flow that the fan never runs after shut down. It only runs after shut down if we were just stuck in traffic with no air being pushed through the grill.

      Correct is best, but I just wanted to let folks know that the crude option does work well.
      It's hard for me to know exactly what these things cost me. I'm guessing a LOT, but I like them, so that's that.

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