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Thread: Thermo fan bypass

  1. #1
    Join Date
    Mar 2009
    Location
    Melton West, Victoria
    Posts
    363

    Thermo fan bypass

    Here's a few photo's showing how to wire up some bypass switches to your thermo fans. As noted by many people the thermo fans come on way too late on the P38 and by the time they come on you are already running very hot. If you know your temp is climbing you're better off switching the fans on early.

    The fans have two speeds - I'll call them low and high speeds. High is quite loud. I turn mine on when I'm doing low range hill climbs and crawling in traffic in middle of hot summer with aircon etc on.

    Wiring is easy - there's two connectors located near the lower left corner of the radiator. Both connectors are connected to part of the aircon system. Simply tap into both these (or one or the other if you only want one speed switch). Personally I ran a piece of 5 core trailer wire through the firewall to the area as it's tidier and easier to work with - 2 wires to each connector. I go through the firewall where Ron has suggested in another post (below the radiator expansion tank)


    I forget which switch is low speed and which is high...
    Photo's were taken with bumper off.

    2 wires go to each connector. The connector on the right (photo's right) only has two wires so that's easy. Yellow and brown wires are my switch wires to this switch.
    Bypass connectors.jpg

    Connector on (photo's) left has four wires - connect to the black and the black/blue wires. Red and green wires are my switch wires to this switch.
    Bypass connectors - Closeup left.jpg

    Switchs mounted inside the ashtray - ashtray removed and bent bit of aluminium in place. Yellow switch is low speed, red is high speed. Knob is subwoofer control. HEVAC waiting for replacement to arrive ...
    Bypass switches.jpg

    That's about it.

    edit: One thing to note is that the 'low' speed won't activate unless the aircon is on. High speed works regardless.

  2. #2
    Join Date
    Aug 2007
    Location
    Brisbane
    Posts
    3,106
    Quote Originally Posted by Junosi View Post
    Here's a few photo's showing how to wire up some bypass switches to your thermo fans. As noted by many people the thermo fans come on way too late on the P38 and by the time they come on you are already running very hot. If you know your temp is climbing you're better off switching the fans on early.

    The fans have two speeds - I'll call them low and high speeds. High is quite loud. I turn mine on when I'm doing low range hill climbs and crawling in traffic in middle of hot summer with aircon etc on.

    Wiring is easy - there's two connectors located near the lower left corner of the radiator. Both connectors are connected to part of the aircon system. Simply tap into both these (or one or the other if you only want one speed switch). Personally I ran a piece of 5 core trailer wire through the firewall to the area as it's tidier and easier to work with - 2 wires to each connector. I go through the firewall where Ron has suggested in another post (below the radiator expansion tank)


    I forget which switch is low speed and which is high...
    Photo's were taken with bumper off.

    2 wires go to each connector. The connector on the right (photo's right) only has two wires so that's easy. Yellow and brown wires are my switch wires to this switch.
    Bypass connectors.jpg

    Connector on (photo's) left has four wires - connect to the black and the black/blue wires. Red and green wires are my switch wires to this switch.
    Bypass connectors - Closeup left.jpg

    Switchs mounted inside the ashtray - ashtray removed and bent bit of aluminium in place. Yellow switch is low speed, red is high speed. Knob is subwoofer control. HEVAC waiting for replacement to arrive ...
    Bypass switches.jpg

    That's about it.

    edit: One thing to note is that the 'low' speed won't activate unless the aircon is on. High speed works regardless.

    For several years I had a V6 Calibra (a b-e-a-u-t-i-f-u-l car ) and the thermo fan arrangement was such that when the car was parked on a hot day, the fans kept running to reduce the effects of heat sink...your wiring gives me an idea ...thank you!!!

  3. #3
    Join Date
    Mar 2008
    Location
    Coogee, South of Fremantle, WA
    Posts
    1,550
    Thanks for the How to, looks very simple. Just wondering if I just make a permanent connection across the 2 wire switch so the fans come on with the aircon will the fans be on low or high speed.

  4. #4
    Join Date
    Mar 2009
    Location
    Melton West, Victoria
    Posts
    363
    Quote Originally Posted by wayneg View Post
    will the fans be on low or high speed.
    If you put the short on the correct switch it will be low speed.
    Last edited by Junosi; 4th November 2010 at 02:31 PM. Reason: Misread

  5. #5
    Join Date
    Mar 2008
    Location
    Coogee, South of Fremantle, WA
    Posts
    1,550
    D.one in 5 mins, easy peasy..... Driving the Holland Track starting tomorrow so extra cooling is there if required

  6. #6
    Join Date
    Feb 2010
    Location
    Townsville, QLD
    Posts
    2,547
    Just looking at this post, does anyone know which of the wires here are for the high speed of the fans? Iím tinkering at the moment and want to play around with manually switching the fans on high speed, but I donít have access to the wiring diagram. I donít want to just go cutting wires for the sake of it unless I absolutely have to.

    From reading this post, it appears that the fan power supply is normally closed (that is, when the circuit is live the fans are told not to run), but when the earth/negative is removed the fans will be triggered to run.

    If youíre super keen to get an idea of why Iím doing it, check out this video series:

    Thermofan Installation Series - YouTube

    Cheers
    Keithy

    2002 P38 Range Rover HSE

    Sequential LPG - Ctek Charger - TPMS - Rear Ashcroft Locker
    Wheel Carrier - Bullbar & Spotlights - 285/75/16 BFG KM3ís
    On Board Solar - Stainless Snorkel - 2Ē Suspension Lift

  7. #7
    Join Date
    Jan 2016
    Location
    Netherlands
    Posts
    561
    I would have to look that up, don't know from the top of my head. However, I remember your thermofan project. Did you ever revisit your original post on here? I updated it a while back with some power experiments: Thermofan over Viscous?

    Wonder what you are thinking

    Cheers,
    -P

  8. #8
    Join Date
    Feb 2010
    Location
    Townsville, QLD
    Posts
    2,547
    Cheers mate, I did a bit of research playing around with the factory A/C thermo fans yesterday afternoon and worked out that theyíre negative switched, and normally open (so applying a negative/earth activates the relays).

    Watch this space!

    Ill go and re-visit the post now! I completely forgot about it!

    Cheers
    Keithy

    2002 P38 Range Rover HSE

    Sequential LPG - Ctek Charger - TPMS - Rear Ashcroft Locker
    Wheel Carrier - Bullbar & Spotlights - 285/75/16 BFG KM3ís
    On Board Solar - Stainless Snorkel - 2Ē Suspension Lift

  9. #9
    Join Date
    Feb 2010
    Location
    Townsville, QLD
    Posts
    2,547
    Itís easier to explain the outcome via video than over typing, so here it is!

    Operation extra-cool with a TWIST - Can I enlist a helper to back up the Range Rover thermofan? - YouTube

    Cheers
    Keithy

    2002 P38 Range Rover HSE

    Sequential LPG - Ctek Charger - TPMS - Rear Ashcroft Locker
    Wheel Carrier - Bullbar & Spotlights - 285/75/16 BFG KM3ís
    On Board Solar - Stainless Snorkel - 2Ē Suspension Lift

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