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Martin,
Get ready to hear all the flack about rehashing a
problem that has already been solved. That aside, I always enjoy a good
engineering challenge. Switching the fans on sequentially is a good thing,
but some will argue that it isn't necessary if the power to the fans is pulled
from another source (such as directly from the battery.) This is the way
that John Hervey made his FanFix. I'm not sure if he still makes themthis
way, though. Despite the simplicity of his design, I prefer the
engineering expertise of the FanZilla. For state-of-the-art fan
sequencing, I suggest a circuit that will toggle between the fans, so that the
first one to come on alternates between right & left. That way both
fans get used evenly and the heat load & cooling on the radiator is more
balanced over time. In addition to switching on sequentially, the FanZilla
also switches them off sequentially. I've never had the FanZilla apart,
but I could unmistakably hear the relays clicking inside. The case onmine
has melted a bit too. I'm not sure if this is from the module internally
or if it is because it has been pushing against a warm wire from the a/c blower
breaker. The FanZilla's fuse holders are still underrated for the duty
cycle they are put through. I suggest something one size larger (in duty
cycle, not amperage.)
You might say that my idea
of alternating/sequential switching of the fans doesn't isolate the
circuits like you want, but with some good engineering practices, this won't be
a problem. Besides, if you wanted it totally separate, then you wouldalso
need separate fan fail lights. One other bug to fix that the FanZillahas
is to shut the fans off immediately with the ignition. Otherwise the fans
run for a few seconds after you shut the car off. When people ask what
this is about, I just say that the flux capacitor is winding down.
:-) I would also wire the fans to not come on while the ignition switch is
in the first position. Otherwise when you are sitting in the car without
the engine running but playing the radio, the low pressure in the a/c
system will tell the radiator fans to come on. Sure, you can stop
this by shutting the a/c off, but if you are only going to be sitting for afew
minutes, it is annoying for the fans to be running 100% duty cycle while the
engine is off. (This might also be the case if the otterstat activates the
fans.)
Another problem with the FanZilla is that it is too
much plug-n-play. It uses the standard relay sockets to run everything
from, but still these spade lug terminals are not very well suited for the duty
cycle that the circuit requires. It either needs larger spade lugs or
(better yet) screw lug terminals. But this would involve cutting wires
& crimping connectors which is definitely not plug-n-play. But what
the hell, if you aren't technically minded enough to cut wires then you don't
belong in the relay compartment anyway.
Walt Tampa,
Florida
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