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  #1  
Old December 14th, 2004, 05:07 PM
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Doug Walker
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Custom wiring question

I want to install a switch that allows me to turn on my AC condenser fans by bypassing the thermostat trigger. I want to route the hot wire from a completely different source. My question is, if the thermostat switch is open, sending power to the fans, and my new switch is also on, will that mean that too much current will be going to the fans? How do I do this properly? (I want this bypass because the circuit to the fans failed off-road this past weekend at the NVTR. I want to be able to apply juice to the fans by an independent means.)

Thanks,

Doug W.
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  #2  
Old December 14th, 2004, 05:18 PM
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You can't send too much current to the fan. You can run a 0 guage wire direct from the battery and the fan will run the same as it does now. A bad fan can pull too much current and burn a wire or fuse. The only concern I would have is does the ECU on your 90 run the fan or is it a simple switch and relay circuit? If the ECU isn't involved, it should work fine.
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Old December 14th, 2004, 06:15 PM
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The wiring diagram shows the power coming to the fans via a relay, which looks like it's partially controlled by the ecu. The fans are turned on either by the AC switch or by a coolant temp sensor. Problem is that that coolant sensor only triggers at 215 degrees and i'd like to get it in gear a bit earlier than that.
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Old December 14th, 2004, 06:35 PM
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Disclaimer I am not an electrical engineer nor have I played one on T.V..

You should be able to run a switched powered circuit to the relay and turn on the fan without any troubles. If you have a week or so before you dive into this project I have a friend who is a LR mechanic at the local dealer. I am pretty sure he has done something like this to a customers 90. What year 90 are you doing this on? I might want to follow your lead as long as I am not going to create a real expensive project.
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Old December 14th, 2004, 06:46 PM
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Well it's a 110, 1993. Different AC than the 90s but probably the ecu connections are similar. Probably if I just run power to the relay trigger circuit, that ought to do it, no?

During the event we bypassed ecu, relay, fuses, everything - just ran hot juice straight from an available ignition circuit directly to the fans, no relay, fuses nothing. Had to get cool -- we were climbing a steep snow covered shelf road in the Trinity mountains after a lot of hard high speed running through mud and whoops. Lost power to a set of lights and all FOUR fans -- ac and aftermarket flexalites both. Temp went to 235 and I shut her down for an on-the-fly re-wire. Saved the engine and completed the 12 hour rally -- no podium this time tho.

DW
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Old December 15th, 2004, 08:04 AM
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Hey Doug, why don't do as in the FAQ sort of and replace that thermostat switch so the AC fans come on allot sooner? Adding a switch as you said will work fine. Both your switch and ECU get power from the same spot (the battery) so there will be no backwards current paths through the ECU. But I like the new T-stat idea as you don't have too do anything and the fans come on, so if you are outside of the vehicle winching and it starts to heat up the fans come on. Anyway just an idea.

Quote:
Originally Posted by F.A.Q.
FINALY! I found the thermostat switch I've been looking for my FL-210 fans. It's the exact same dimensions as the AC cut-off switch that screws into the thermostat housing. I had taken the AC switch to an auto parts store before and found a fan switch off a Porsche that looked right only to find when I got home that the threads were slightly off. This time, I took the thermostat housing with me as well as the AC switch and hit a different store. The guy there was really into what I was doing and helped try a bunch of fan switches until we found one from a Volkswagen that was perfect. $15 complete with gasket. I like it a lot better than the bourdon tube deal that comes with the fans. It's marked in Celsius as 92/87C which is 198/189F. The thermostat is 88C or 190.4F so it should work perfectly and is a much cleaner installation. If it works out. This is a mod anyone can make to their 90 even if they have AC since you really don't need the AC switch. It's just a switch that is normally closed and will open to prevent the AC compressor from running if your engine is overheating. I cleaned off the AC switch so I could see the numbers on the side. It looks like it's set to open at 109C or 228F. So, your rig would have to really be cooking before it kept your AC form running. Oh yeah, the fan switch is Beck/Arnley Worldparts Corp. part no 201-0809

Chuque Henry added: FYI Pep Boys helped me look up the part (Beck/Arnley 201-0809) and found it's the fan switch for the following Volkswagen's:
75-84 Rabbit
80-83 Jetta
74-80 Dasher

and now, back to garage,
Rob :-)
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Old December 15th, 2004, 02:36 PM
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Mike, many thanks for digging that out for me. Sounds like a great solution. There is a coolant sensor for the EFI as well, how do you know which one is which -- AC vs. EFI?

DW
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Old December 15th, 2004, 02:43 PM
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The AC one has 2 wires and is on the T-stat housing. Then the other one in that area is for the Temp gauge and only has one wire. You want to chang the AC one
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