Heater troubles

[hoodsy]

HI folks, haven't been here for awhile, but since I was last here I finally got my 412 on the road, government safety inspected and emissions inspected. Passed with flying colors. only took me about 13 years haha. Thanks for all the help I got from you guys. Now to the heart of the matter. My heater keeps blowing the 8 amp fuse. I have changed out the high temp sensor, and it seemed to work for the first tests, and then back to the same old story. It blows the fuse almost immediately. there is no continuity across the sensor so it should be good. even if I move it out of its position it still blows the fuse. this is basically what was happening with the original sensor. It would blow after a few minutes. I have checked the ducking for blockages etc. all should be fine. I don't think it is a problem with the sensor or overheating as It will blow the fuse whether it is in position or not. anyone got any ideas? I am about to try and see if there is a bad wire somewhere, although I doubt it. could there be a problem with the dash switch or could something else be drawing too much current. also my dash fan seems to always want to pull air from outside even with the dampers closed. all the damper seems to do is stop airflow to the mid dash aft facing vents. hopefully you guys will have a bit of insight. thanks

[hoodsy]

I am also looking for the right angle duct piece for the passenger side heater tube in the engine bay, next to the aircleaner. If anyone knows a source for this part please let me know. Also I notice the california imports has some aftermarket insulated tubes for heater box to body connection. they list them as being for buses, some bugs, and type 3's. they look like they may work on the 412, does anyone know anything about these. and should I have insulated tubes from the heater boxes to the heater, as well as from the heater to the body. Or should they be just from the heater to the body. at present I have regular hoses from the heater boxes to the heater, and the insulated ones from the heater to the body, although I will be replacing one of them, as it seems at some point it got too hot and no has a hole in it.

[raygreenwood]

By high temp sensor...do you mean the small one about the size of a dime and disc shaped inside of the rubber plug on top of the unit not far from the coil? If so...is the fuse it is blowing the inline one inside of the engine compartment with the olive green wires leading to it?

If not...then it is not clear what fuse is blowing and wich safety sensor you are speaking of.

If I am correct....then you should NOT have an 8 amp fuse in that position. That is either a red 16 amp or 30 amp blue fuse that goes in that position. I will verify. Ray

[hoodsy]

HI Ray, yes the high temp sensor I am referring to is the one about the size of a dime mounted on top of the heater. The fuse that is blowing has on red wire going in one end and two red wires on the other. according to my manual I believe this is supposed to be 8 amp. the other two fuses are 16 and 30. I have a varient so all are under the backseat.

[wildthings]

The wiring diagram shows a 16amp fuse, though since it only feeds the fuel pump I don't know why it would need to be that large.

http://manuals.type4.org/ba4/ch1/ba4_11f.html

[hoodsy]

In the wiring diagram, it is part#16 ( 8 amp fuse). the overheating fuse.

[raygreenwood]

Let me check my notes. If you can definately trace the fact that the wire to the fuse in question is going to the high temp sensor.....then in my experience what i had to do was pull the rubber sensor plug out...pop the sensor plus its wires out of the rubber cover....not easy with short wires....and test the sensor itself.

What I found out happened is that when I had the sensor out before and I pushed it back into the top of the heater....I pushed too hard. The little disc has a tab on each side and if memory serves the wires are either crimped or soldered....but they have to stick straight out from the disc sides. If they are rolled or bent...the body or disc of the sensor becomes a conduit to the wire on teh other side.
I beleive the disc is assembled as a two-sided device....one side has a tab for + wire and another for the negative. The bi-metallic switch and spring inside connects them together and shorts to ground blowing the fuse.

So if either wire tab is bent at all and contacting either the edge of the disc body or the chassis of the heater...it will short. This is how I ripped the rubber outer sheath...yet another part I need to recast.

By the way...sorry for the delay in casting the parts in question. Lost of false starts when I have been away from this for a while. I just found a platinum cured silicone that will do the job and is affordable.....the last one I selected by the list of its ultimate qualitiesfrom one of my suppliers.....turned out to be $1,245 a gram... ..WTF!
Next...the vacuum plate on my Bell jar crapped out...hello E-bay!. I will have these done before Christmas. Should be quite cheap actually.
They will be 30-35 durometer and good to a constant 500F. Ray