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Heater

The car had also a very rare part: a petrol heater. it all looked pretty much beyond repair when i removed it from the car, but i decided to at least try if it could be repaired. The heater consisted of four main parts: a fuel pump, an air pump, a heat exchanger and a mechanical regulator.
In this picture you see the fuel pump on the left, and the regulator on the right, the black box with the connectors on it. This is the 'after' picture, of course. The lower hose goes to the fuel tank, the upper hose leads the fuel/air mixture to the combustion chamber.
This is a picture of the main heater parts, all neatly tucked away inside a compartment. On the right, under the black bracket, is the air pump, which sucks the fuel-air mixture into the combustion chamber (left, red). The combustion chamber has a glow plug, which ignites the mixture. A blower then transfers heat into the normal heater pipes. The exhaust fumes exit below the car, through an exhaust, which runs to the back of the car.
By the time i had everything cleaned up and ready to try, i still had to figure out the mechanical regulator. it looked like some sort of timing device, but i was unsure about it. 

 

Anyway, what is there to time? Just switch it on right? So, i tried that (fire extinguisher at hand..), and to my surprise the thing worked right away! After a few minutes (garage turned blue) i switched it off, and disaster struck. The fuel pump started leaking fuel, and not a little bit.

So, i took the pump apart but found nothing wrong. The design of the pump was such that a compartment gets filled with fuel, and only if there is air flowing some fuel drips into the air stream. Clever safeguard, but what about the leaking? As it turned out, that is what the timing device was for. When the heater is switched off, the air pump, glow spiral and blower need to be run for a few minutes longer to make sure the fuel pump is run dry. That's all..

So next thing was to think up some timer. Instant on for all groups, delayed off for glow spiral, air pump, and blower. Any electronics freak now has that magic number in his head: 555. So, i designed a simple timer, adjustable from 0 to 4 minutes, and put it in the original timer housing. 

 

This is the regulator i designed to get the timing to work properly. It is a simple, 555-based timer design, if you are interested just send me an e-mail for the schematics and PCB. The original, mechanical switch was so badly rusted that its workings were impossible to comprehend, but the box suited just fine for the new timer.

 

After adjusting the timing (about 3 minutes seemed to do the trick), the heater is working a treat. You will not believe the amount of heat this thing produces. Blows the fog off all windows in those wet and damp winters over here. A word of caution: when i sent out some messages in the porsche newsgroups, many people warned me of this device, it can easily burn your car to the ground if anything goes wrong. Quite logical actually, if the timer doesn't work properly or you run the battery down (it uses about 12 Amp when operating!) the fuel pump will spill petrol right into your car. So please be careful if you ever decide to rebuild one.

 

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