Sam Woodson wrote:
I had the AC fixed, now that the AC is fixed, after running it awhile, the fuse #17 a 25 amp will start to Melt, then blow.
My mechanic has looked at it all morning. He said he shows a 10 amp current draw across through the fuse/circuit.
He checked out the blower motor, the control unit, etc. Everything seems to be fine.
He is taking it to another guy this afternoon that just deals with electrical car issues. Just thought I'd check with the list first for any pointers.
Having the fuses "melt" isn't unusual. The connection between the fuse and the fingers will get corroded (or just lightly oxidized) and that
creates resistance. The fuse then gets hot, gets soft and starts to compress.
The solution is to clean the fuse holder well and the ends of the fuse. Also, using fuses that have a ceramic body will stop it from melting.
Dirty contacts for the fuse -- acting like little heaters so that even though the current isn't enough to blow the fuse, it still heats up.
The fresh air blower takes the power from the the resister assembly in the air duct, and that is fed by the blower switch. From there on it connects to the blower relay and finally to the main 12v supply. The circuit is pretty simple.
Since the relay, blower switch and the resistor assembly don't have a ground connection you can rule those out from creating an overload. It is unlikely but a wire insulation failure could be causing a short circuit.
But most likely the blower motor spins badly and has a tendancy to get stuck. In that case it takes a bit of time for the blower resistor to overheat or the temp overload in the blower itself to kick in. This might cause an overload on the fuse and burn it. So my advice is to carefully check the freely running of the blower. See if the problem still occurs when the blower is disconnected at the blower plug (likely not, so insulation is ok)
I've seen blowers make funny noises when turning, indicating a dry or bad bearing. An owner in Germany made a hole in the blower motor top of the case and dripped some oil in. No, it is not designed to lubricate externally :) Plugged with a rubber pin. Was perfectly ever after.
1992 928gts Midnight Blue
1988 928s4 Cherry Red (Sold in 2006)