Gentlemen:
Stranger and stranger!
Just went out to the garage and did 2 tests:
Test 1: I took the out-of-the-car BJ8 blower motor assembly to the bench
and connected the leads both ways several times - the motor ran in the
correct direction no matter how it was connected to the battery. Period.
The bulk of the air was blown out of the outlet port on the case, although
there appeared to be a bit coming from the inlet port. With the inlet hose
connected, I'm sure that the fan would move all of the air in the right
direction as it always has on the car in 20+ years of driving, regardless of
the car's polarity.
Test 2: I temporarily interchanged the heater blower leads on the
on-the-road BT7 with the whole thing in situ on the car - this is a very,
very original gold level concours BT7 top-shift tri-carb, which I have run
NEG ground for 10+ years without ever noticing a heater air delivery
problem. Result - absolutely no difference in air delivery at the outlets
either way.
Conclusions? All I know is that any Healey that I've done a polarity
conversion on has had the heater air delivery system continue to work as
before without interchanging the blower motor leads, notwithstanding the
fact that the systems were pretty anemic right out of the factory. I wasn't
aware of any polarity sensing electronics built into the blower motors
themselves, but it must be there (thanks Jim). I know for sure that there
are no diodes etc. in my tri-carb's original wiring (we won't talk about the
Pertronix ignition here, right!). I'm also pretty sure that the blower
motor spec did not change throught the 6 cyl. production, but I could be
wrong.
I strongly suspect that the original poster (sorry, I've forgotten who) that
had the air reversal problem has an almost total air blockage somewhere
beyond the blower motor.
I'd like to say that I've learned something from this thread, but if I have,
I'm not yet sure what it is - other than my Healeys don't have a problem in
that area. I would welcome more comment from any lister with more knowledge
of these things than I, who can explain these results. I can't account for
David J's results in similarly bench testing an old blower unit this
morning.
Let the flames continue!
Earl Kagna
Victoria, B.C.
BT7 tri-carb
BJ8
Subject: heater fan sucks
> I have converted at least a half dozen Healeys to NEG
> ground, including my present two, without interchanging
> the blower motor wires - they've all continued to move
> air in the right direction.
I don't doubt that for a moment . . . but the reason is not the permanent
magnet motors. Diodes in the wiring (or integral to the motor) will maintain
the polarity seen by the motor regardless of the polarity of the wiring, so
the motor will always spin in the same direction.
Jim Hill
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