User 4221

I've heard lots of stories about the engine compartment blower (HVAC) failing and catching fire.

I haven't heard what usually causes this. Does is lock up, draw too much current and melt?

Do the coil windings fail and short?

I'm curious because it may make sense to put a fuse inline with the blower next to the unit so an extra level of protection can be done.

Anybody know the failure mode?

Tx,
Scott

Ed Hughes

Seems to me like more issues with the blower under the cowl catching fire are reported...

User 4221

Or the footwell blowers.....

rusnak

The front ac condensor blower catches fire, and when it does, I'm told the flames go shootin out the trunk when it's opened.

Ed Hughes

Those will squeal like a cat first.

theiceman

i have had my engine blower fail a couple of times and no real issues as they just wear out and fall to bits .. the one at the front .. now there we have an issue ... fire and brimstone and the like ..

g-50cab

Think it's the front is the only one that's not fused that will give you issues - pretty sure the rear is fused.

In a Carrera - I'd be much more worried about the aging fuel line. The rubber cracks - the cracks allow fuel to drip onto a hot engine. They tend to burn real good.

User 4221

Thanks, guys.

I must have had the fans reversed in my mind.

I'm replacing all the fuel lines as we type, so I'm looking for other areas to "harden" while the car is down.

I will check the schematics on the front blower and see about fusing if it makes sense.

Lorenfb

"Anybody know the failure mode?"

1. The brushes wear-out.
2. The bushings fail causing the armature to seize resulting in high currents
which can cause wires to burn.

rusnak

Yep, usually the brushes wear to the point that one of them falls out of the holder. I've had this happen more times than I can recall. At least 4 times, and I'm probably going to replace the 5th one this year. I've not had a rear blower catch fire. It's fused and has a relay, but neither the fuse nor the relay has ever blown, so I don't think that's the answer.

Lorenfb

"It's fused and has a relay, but neither the fuse nor the relay has ever blown, so I don't think that's the answer."

Right, the assumption is that the correct fuse was used which is NOT always
the case. As the bushings wear, more current is demanded and a larger
fuse solves the short term problem, e.g. For the techs over on the
'Dark Side'. In the end, the wires potentially burn or the motor itself,
i.e. armature windings get smoked. It's that simple!

But again it could be, "earth-crossing asteroids".

rusnak

Loren, I am in agreement with you that the motor or the wires burn eventually.

In the stock configuration, with fuses specified in the original Porsche diagrams, there are both a fuse and a heater blower relay.

What I'm saying is that neither one has ever blown in my experience, and I've been through two factory blower motors, and 3 or 4 replacement motors. Never has one caught on fire, but the motors and the wires get very very hot when the brushes finally give out.

Did I say to use a larger fuse? No. That's because I already said that I've never had one blow - not once in all of that time.

The question was "does a fuse protect against potential fire damage". I'm saying that (1) there already is a fuse, and (2) the factory fuse does not blow when the brushes wear through to the armature. What happens, and I think we are in agreement, is that the current keeps flowing, and the motor stops turning, producing a lot of heat, but not enough to catch fire. At least NOT YET.

Therefore the LAST THING I would do is put an even larger fuse on there. If anything, but a smaller fuse in there.

Lorenfb

"Did I say to use a larger fuse? No. That's because I already said that I've never had one blow - not once in all of that time."

No, not you, but the typical tech-weenie on the 'Dark Side'.

Ed Hughes

Ahh, but we know rusnak is the typical tech-weenie on the RL side!

I think I'm staying away from the dark side too, check out the Zuffenhaus wheel thread that thankfully died on Saturday...

User 4221

I saw that debacle..... I typed out three different posts and deleted them before sending as they were not very nice.