i have also done the same on a few cars now, i run a three relay set up now that has one for each fan switched by the thermo control switch such as a davis craig or ice one and the third relay is switched by the a/c clutch wire so when you turn on the a/c it pulls one fan on only. the car runs cool, the a/c runs cool and the whole set up cost $150 for the fans, $60 for the thermo switch and $24 for the relays and some connecters. took about 3 hours to put in and wire up including getting rid of the god awful clutch fan.

Yobboford, would you happen to have a wiring diagram (sketch) how you wired up the relays, as that sounds alot cheaper than the $300 BPT harness? The BPT looks llike a great setup but the cheaper I can get out of it the better.

Theres a doco here on Fordmods which details how the relays operate

Sounds like your fans are cutting in at the same time and drawing a large load by doing this. With two switches you can stage the fans and therefore have less shock load on your charging system.

Alternatively have one hooked to the thermal switch and one hooked to the A/C compressor.

just thought I'd give you a quick update.

today I've

-removed the clutchfan
tried for about 1/2 and hour using conventonal spanners and only
succeded in removing skin from knuckles so I bit the bullet and made
the spanner in the workhop manual +1hour more
-trimmed the the new thermos to fit
jayair el fans didn't quite fit but I do have a 3core radiator. radiator
came marked eb so should be the same as yours.
-mounted the davis craig temp switch and relay
using diode to draw input from the air-con clutch wire without
activating the compressor everytime the thermo's fire (this saves
using 3 relays).

tomorrow I hope to
-feed main power
am about to go searching for an ignition switched wire to power
the fan's up and calibrate it.
-black box
hope to make an electronic controler taking the air'con and davis-craig inputs and incorperating a timer circuit so when the temp switches one fan comes on and if the temp stays high for a set time (yet to be confirmed ~7sec) the second fan comes in also need to alow the air-con to use single fan operation unless temp timer kicks in. would also like to change which fan kicks in first so they get even usage. am also considering trying to get an input from the speedo to stop air-con switching fan at highway speeds but that will be a bit harder.

sorry update was not so quick

Several good ideas there, but why don't you just put another thermal switch in. Set it a bit higher than the first and wire it independently of the A/C line to the second fan?

This way if fan one activates but fan two doesn't then you know that one fan is sufficent. If you wire up a "time delay of 7secs" you will only result in both fans switching on and off constantly, causing excess wear tot he fans. (Electrical stuff likes to turn on and stay on! Constant on/off operation can cause shock to the components).

As for the speed thing....a good idea, but I will be interested to find out how you are going to do it!

Wire another relay in to allow independent operation of the A/C. Cheap and easy!

Your ignition power source (not constant or actual supply power) should be from the fuel pump relay.

the main reason for trying to do it electronicly and not using 2 termal switches is not that their ugly (they are, and due to the length of the copper probe difficult to hide). but I want to set it up so the fan which start's first alternates am also mulling over a soft start for the fans.

time delay was just an idea for a temp setup untill the electronis are fully sussed but ive just got both fans working simultaniously (pops 25A fuse on startup)

am looking at termocouples as I do want to use temperature triggering, also I have some tc wire lying around, unfortunatly it has braided insulation (not water tiight)

as for the speed sensor i'm thinking of taping the neutral safety switch and tacho feed. If I know it's not in neutral or park and doing over 1000rpm i'm not going to need a fan for the aircon.

fail safe I intend to have the davis craig as a fail safe switch set a bit higher than the electronic triggers and maybe put that in the bottom hose. that will alow me to conceal it much better. and make it easier to seal the hoses.

main thing slowing me down at the moment is electronic knowledge am going back over my notes on transistor theory much rustyer than i'd hoped could take a while

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