hi guys got a weird one here well it is to me removed the blower & connected to a battery all good runs sweet , checked the fuses all ok connected blower up nothing checked the wiring no power ? should i just hardwire from the battery or take it to a auto electrician ?

 

Ac fan has basically 2 circuits. One is full speed , which bypasses the 'speed transistor.' The speed controlling transistor is hidden in the main outflow duct for cooling (held in by one little screw)! The second circuit is 'all other speeds,' utilizing the 'speed transistor.' Quite commonly, the power supply to the fan poops out back at some trace on the fuse box (driver side USA). A common fix is to bypass the fuse box and wire directly to battery (with appropriate in-line fuse). The wiring is easy, BUT BE SURE YOU USE THE CORRECT POWER LINE into the fan circuit and disconnect the leg coming from the fuse box. I did this after PO wired power from the cig lighter failed...nice!

The other possibility is a bad AC control unit...but this is rare...

read through the wiring guide. It is really helpful.

 

I checked all the wiring there was power there but I only think it was about 6 volts as the tester I have has 6v 12v 24v and the 6v was lighting up but with the fan connected to a 12v battery it worked fine but not with the plug plugged in ?

 

Does the blower motor run when the controller is set to the highest fan speed? As XRAD said, when set to full speed, the controller bypasses the power resistor (AKA the speed transistor; Land Rover uses the term power resistor in the workshop manual). The function of the power resistor is to lower the voltage going to the fan, thus reducing the fan's speed.

We recently had the same problem in my sons Honda CR-V. Its system works on the same principles. We replaced the power resistor and all has been well since.

 

Many automotive blower fans use the resistor method for controlling fan speed. Wherever it's called a transistor is technically incorrect. It is a resistor that modulates the voltage to the fan at lower speed settings. This is why the manual calls it a resistor. Basically I'm just reiterating what mln01 has already said.

All that technical BS aside, it's likely that if you fan works on the bench, and on high, your resistor is bad. I can't tell you where it's located on a Disco, however in my experience it's been a PITA to replace on most car blower fans I have had to do battle with.

 

True, 'technically' the little unit is called a resistor, and that's how the circuit functions, but it uses a 10$ NPN transistor controller to regulate the resistance. I have replaced this transistor on my controller, which is why I use the term 'transistor'....

BTW...there are many similar versions of this resistor unit as found in similar era jag's and other EU vehicles, and which can be had for a way cheaper price than the LR version. Some of the transistor circuit mounts are slightly different, but the guts are the same. With careful de-soldering and re-soldering, you can rebuild the original LR unit....if this is the issue...

or buy a new on for 200$....

so...if the fan works great hooked up to battery, the fan is not the issue. there are two relays mounted to the blower box (high up on pass side and in rubber mounts) sometimes one of these may crap out, but unlikely...

1) review the electrical diagrams and follow the harness connections so that you understand them completely
2) check to see if someone already rewired or bypassed anything.
3) replace the power resistor?
4) run a new main power line from battery? ( i only had to tap into one line at blower harness to get it all to work...ie: the one from the main fuse block )
5) maybe its the AC controller head unit?

 

Well, there you go. All the old euro cars I've dealt with have what really amounts to a giant copper winding/spring inside a ceramic or metal housing. Been working great for decades. Leave it to modern engineers to overcomplicate something that used to be a simple setup.

 

I checked it all again fuses and wiring when i had the ignition on it was giving me the reading of 12.1 , checked the blower fan again on the battery and it worked just when i connected it to the power it didnt work on low or high speed so it looks like a hard wire from the battery

 

On number 4) run a new main power line from battery? ( i only had to tap into one line at blower harness to get it all to work...ie: the one from the main fuse block ) you mean the red and Brown wire ?

 

I faced a similar situation a few years ago..... see my post #14 here... it was one of the two relays... rust inside the relay:

https://landroverforums.com/forum/di...r-85189/page2/