BobbyT

I've ordered a new one of these for the engine bay blower, but I don't know exactly what it does....comments, please.

The blower circuit has the ballast resistor, a temperature sensor (both of these located in the hot air duct), a two-stage relay, and a 30-amp fuse.

maurice97C2S

You can think of all the 'ballast resistors' in the 993 in the same way .. they are an electrical 'dummy' that will, for instance, slow down the speed of a fan. So the fan gets two 'speeds' which meet different parameters of operation.

A resistor is just an electrical load which does no useful work itself ...

HTH, cheers, Maurice

sidned

Definition: A resistor in the primary ignition circuit that lowers voltage after the engine is started to reduce wear on ignition components.

Or:

an electrical device that resists the flow of electrical current

That's the technical explanation, but I'm sure someone can chime in with the reason why the engine fan needs one....

BobbyT

Thanks, guys...and one more question. The ballast resistor has two wire, both with the same type of terminal. Does it matter which wire connects to which terminal on the resistor?

Bob Rouleau

Resistors have no polarity. Either way you connect it, it is the same.

Regards,

BS911

Now the ballast resistors in the front have a very different definition.

Ballast Resistor: Small, ceramic disc resistor serving to provide low speed fan operation - for about 5 to 10 years, after which, you discover that they are small piles of ceramic dust tucked up into the inner bowels of a 993 fender. They are strategically placed close enough to see, but not quite touch. Far enough out of reach to require removal of surrounding parts, but close enough to make you try for at least a half hour without removing said parts. Cheap enough to replace at whim, a pain enough to deal with that when one discovers their failure, they wait at least a year before trying to replace. These ballast resistors are so elusive that most failed resistors still live in their original place, taunting owners who have relocated new resistors to more friendly locations. Others merely short circuit the fan blower relay, utilizing high speed fan settings only.

I just replaced BOTH of mine this weekend, can you tell?

Dudley

Brian, Well described! Obivously a veteran of this testy DIY.

MadMarkie

Is there any disadvantage to bypassing the resistors and running both the oil cooler and AC fans on high speed? I am planning an auxiliary oil cooler installation soon, and need to decide whether to replace the ballast resistors with new parts, or short around them with some nice heavy gage wire. Any thoughts from the electrical gurus out there?

BS911

You can jumper the relays in your fuse box on the relay input side, not the output side. Doing the input would then not require the jumper to carry the load of the fan, it only holds the load of the relay. I don't have the pinouts handy, but you basically bridge the input on the relay for the slow speed fan to the input on the high speed fan. (I think that is terminal 87 and 87C on the relay.) Check out p-car.com for info on this too.

The disadvantage is that when the high speed fan runs, it puts more of an electrical load on your system and you hear a "whirrrrrr" up front. The upside is that your car will run cooler sooner if in very high heat conditions. In Tucson, that might not be so bad for you.

I ran "jumpered" for a long time, thus my post above. I just wanted to get back to a low speed setting for... the sake of ... bloodying my knuckles on this DIY I guess. No wait, there had to be another reason. Originality? Nah. hmmm.

MadMarkie

Thanks Brian!

I am currently running a jumpered relay for the oil cooler fan as you described... but I usually end up using the manual switch before the fan kicks on anyhow. I figure since I will have the nose off for the aux oil cooler, I might as well replace the resistors... I could always jumper at the fuse box again if the low speed doesn't cut it.

Cheers, Mark.

all623

I am trying to address the fuse blowing for the oil cooler blower. First step says to swap relays R04 and R14. I turn the blower switch and air is blowing into the cabin. For the heck of it I removed both relays and I turned the "blower speed selctor switch" on and the fan is still blowing air in the cabin? This doesn't sound correct? What I am interpreting incorrectly?

all623

A/C condenser fan...