How to add a fan to AC on a 92 740?

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geronimo - 23 Oct 2006 17:40 GMT

The original two speed fan fried, and we don't want to spend the big
bucks for an OEM fan. I installed a engine fan out of my defunct
Mercedes 300. We have another fan, a smaller one, and want to put it
on/in front of the AC condenser, and wire it in so it comes on
whenever the AC is turned on. THe big round Mercedes fan is positioned
on the other side of the radiator, so it is not drawing air directly
over the AC condenser. It its simple enough to find the fuse for the
AC compressor, and tap off power BEFORE the fuse to an new fuse for
the AC fan. I think when I measured the current it draws about 7 or 8
amps. Question is, I need to know whether the circuit that switches
the AC compressor clutch on can handle another 8 amps. Or should I to
be safe only power the fan through a booster relay?

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Roadie - 23 Oct 2006 20:31 GMT

> The original two speed fan fried, and we don't want to spend the big
> bucks for an OEM fan.

Did you look for a used one from the boneyard?

> I installed a engine fan out of my defunct
> Mercedes 300.

Does it work and keep the engine within operating temperature??
It bolted up to the shroud ok?

>We have another fan, a smaller one, and want to put it
> on/in front of the AC condenser, and wire it in so it comes on
> whenever the AC is turned on.

Why do you want to add yet another fan. Sounds like something isn't
installation working properly and you are trying to override it with
yet another fan.

So you will have one smaller fan in front of the bigger fan? Is the
bigger fan also triggered by the AC system? I would worry about the
smaller presumably lower volume fan actually being an impediment to
airflow of the larger fan.

> THe big round Mercedes fan is positioned
> on the other side of the radiator, so it is not drawing air directly
> over the AC condenser.

It should be pulling air over both the AC coils and the radiator coils
if it is correctly installed.

> It its simple enough to find the fuse for the
> AC compressor, and tap off power BEFORE the fuse to an new fuse for
> the AC fan. I think when I measured the current it draws about 7 or 8
> amps. Question is, I need to know whether the circuit that switches
> the AC compressor clutch on can handle another 8 amps. Or should I to
> be safe only power the fan through a booster relay?

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James Sweet - 24 Oct 2006 00:10 GMT

> The original two speed fan fried, and we don't want to spend the big
> bucks for an OEM fan. I installed a engine fan out of my defunct
[quoted text clipped - 8 lines]
> the AC compressor clutch on can handle another 8 amps. Or should I to
> be safe only power the fan through a booster relay?

If that fan isn't enough to work on its own why don't you go to Schucks
or similar place and pick up an aftermarket fan of the same size as the
original? They're around 100 bucks which is a chunk of change, but much
less than OEM.

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geronimo - 25 Oct 2006 05:04 GMT

>> The original two speed fan fried, and we don't want to spend the big
>> bucks for an OEM fan. I installed a engine fan out of my defunct
[quoted text clipped - 13 lines]
>original? They're around 100 bucks which is a chunk of change, but much
>less than OEM.

The one big Mercedes fan is enough on its own to regulate the eng.
temp fine, cooling adequately. Realized that it is the trans cooler
that is on the far left front of the radiator... there is a open area
on the left of a few inches not covered by the Mercedes fan, just on
the side where the trans cooler is...the aux fan therefore isn't
impeding air flow trough the main engine fan, as it is on the far left
of teh radiator. The aux fan then is helping pull more air through
the trans cooler.... that is all, and may not even be necessary.

Thanks, Geronimo

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