Right, lets figure this out.
I had a similar prob - blowing fuse on high speed. I think I was up to a 20amp fuse and a hot fusebox before I got fed up and decided to pinpoint the cause!
Basically (in theory) the relay circuit draws little on the primary (fusebox) side. All its doing is powering a switch (the relay) to carry current via the other two cables on the relay which are rated for the job. I'm asuming you understand how relays work. (
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My fuse kept blowing too and it shouldn't because one assumes that the relay is doing all the work right? Now, that can only change if there is (for whatever reason) resistance in the primary circuit, it will cause the circuit to get warm and blow the fuse, or cook the wires or fuseholder if the fuse rating is too high. Took me a while to isolate it but all it needed was to remove the relay, clean the contacts and re-seat it a couple of times. I also removed the relevant spades from existing fusebox and fitted an inline fuse but you may not need to do that.
If your 16amp fuse is blowing, you can bet that circuit is getting a tadge warm, and you can check connections to back of fusebox to see if they look like they have heated up. It only takes a duff connection on the relay or connections to fusebox to have this issue. Try removing relay, giving it a good clean, and pushing it back into its socket - chances are the problem will vanish. The relay could be faulty but I'd suggest its unlikely and this will be down to corroded contacts. It nearly always is.
Do
NOT fit a bigger fuse - sort the problem out or you'll have a fire. I think you're not quite grasping how the relay fits in here and drawing the wrong conclusions as a result. The wiring is in all probability correct - just dirty. The relay in particular can get just as corroded as earth crowns.
In answer to:
Shaundon wrote:
at high speed it goes back up via the red and blue wire and then connects the relay coil to ground and thus connects the other red and white wire from the fuse box via the relay contacts to the red wire that goes back down to the fan.
It doesn't. The primary circuit goes live when you switch to high speed, switching the relay on the secondary circuit and passing current to the fan via chunkier cable. If it ran from the primary circuit (like low speed), it would blow the fuse instantly. The draw from a motor can be substantial when its going some, which is why nearly all car fans and motors have to use a relay. No fusebox could cope with that.
