I've looked at the wiring diagrams, searched the threads, and spent big money and still no solution. Have a new to me 03 Discovery. Last on the list of grievances is that the AC fan motor only runs on high. I replaced the resistor pack with a budget option from Rockauto and replaced the fan motor while I was down there. I have a spare climate control head unit I also swapped in that made no difference. I read some forums that said you can just replace the transistor on the resister pack which I also did. I checked the ground visually on the passenger footwell though I still need to ohm it out. Any other ideas or is it possible that it could STILL be the resister pack?

 

With all those parts, the system could be set up and checked out on the bench. The way it is supposed to work is highest resistor in series with the motor gives low speed. No resistor, direct connection to the motor gives high speed. Intermediate resistor values in series with the motor give intermediate speeds.

 

I'm going to check to make sure it has a good ground from the resistor pack to the chassis. I assume the two wires that run to the climate control head unit output some level of voltage so I will check that as well. There is obviously continuity between the motor and resistor since it runs.

 

I had the same issue, replacing the resistor fixed it as expected. Could you have a defective resister out of the box? Especially with a cheaper one. I got mine on ebay, $33. still works fine.
https://www.ebay.com/vod/FetchOrderD...&segname=11400

 

the link doesn’t work. Anything is possible. Should have bought the Atlantic British one from the get go but saving 100.00 was too tempting. Stupid me trashed the box before installing it so now rockauto want take it back.

 

With an ohm meter, the resistors can be measured and checked.

 

Well upon further diagnoses I may have identified some issues. I removed all the components from the old resistor and at the least found that the thermal fuse was blown. I took apart the new one and the only thing I think was wrong with it was that the resistor seems to be bad on the collector side. I tried to swap components but in the process I think I over heated the capacitor as it no longer has continuity. Wiring in the truck seems to be fine. I could order all the components to rebuild the resistor but part of me just wants to spend the money and have a definitive answer.

 

It is VERY hard to overheat a capacitor. When you say "continuity", do you mean you tested it with an ohmmeter, or continuity tester? If so, you've learned nothing as a capacitor will show no continuity. That's the way they work.

 

Ohm meter but I just tested again with a continuity tester and I think it's fine. Either way I ordered a new one and relay from AB, I can always send it back if I don't trash the box this time lol

 

Well I installed a new relay and resistor from Atlantic British which did not resolve the problem. At this point I am out of ideas and guess I will just live with the fan speed being on full.