Engine mounted heat blower dead

[Chris Lovell]

My '88 Cab electric blower (mounted above the engine) has stopped working. I checked the possible fuses in the front trunk and they seem okay. Also pulled the fan-blower and tested that on a 12v source and that works fine as well. Then I tested the wire delivering power to the blower and that connector is dead (ignition in full power setting and heat levers up).
Can anyone tell me if there are other fuses (passenger footwell or engine compartment) which are worthy of checking? I also have this nasty feeling about mice in the car again. Anyway, I'll check everything before I trace the wiring for rodent incursion.
Thanks,
CL

[hcoles]

sub. I think mine is dead also

[DRACO A5OG]

I think your year has fuses at the foot blower up in the cab

[dhagood]

Originally Posted by DRACO A5OG

I think your year has fuses at the foot blower up in the cab

draco, i think this is true as well, but the rear blower is a different beast.

have you checked the heater blower relay on the left side of the engine bay under the plastic shield? if that goes out, none of the heat blowers will operate.

[DRACO A5OG]

Before the heater went out, did you smell a plastic burning smell? that would be the foot blower fuse.

Dhagood, I agree the engine bay relay is a nightmare if it goes out.

[aj88cab]

The fuse (25A) for the engine compartment blower fan is on the electrical panel in the engine compartment (under the palstic cover on left side), the previously mentioned control relay is there too. Thge blower fuse is on a 3-fuse block that also includes control power for the blower control relay and the rear window defroster if equiped (your's is a cab like mine and will not have the defroster circuit).

Check continuity from the blower connector to pins 5/6 on the control relay connector.

Also check that the circuit & contacts on the red levers are working properly (12v at pin 9 on the control relay connector with lever up/ingnition in ON position).

If the above check out OK, then it is probably a bad control relay unit.

[hcoles]

I wish I had a simple single line drawing of the power and controls for all the electrical fans with notes for where each component is found. I started one by looking at Bentley but gave up. Anyone have one they or another made?

[Chris Lovell]

Andrew,
This is very good to know. I have definitely not looked into the electrical block in the engine bay. I will do so soon. I will check the 25A fuse and test the block for power and continuity. I will let you know what I find. I am hopeful the Bentley will give some further specifics on which control relay is of interest etc.
Thanks,
Chris

[aj88cab]

Chris

The blower control relay looks like this, most likely the 25A version on the left:


And is located here mounted in the (empty) center position. See also the fuse locations.



Pull the relay and make all the above tests at that connector.

The easist (only?) way to test the relay is if you can borrow a known good relay from a fellow Carrera owner and try it in your car, if the fan runs, your relay is bad...not exactly high tech, but it works

Good luck,
Andrew

[Chris Lovell]

Just how cool are those pictures!! Thanks so much Andrew. I happen to have another 911 which is tracked and therefore this relay will be available. And just my opinion but ... I think this particular fuse block is so outdated looking, it could be from a 1958 VW beetle. Probably was... anyway, many thanks.
Chris

[Chris Lovell]

Andrew and all, the engine compartment fuses are fine. Pins 5/6 have continuity to the positive connector at the blower motor. Pin 9 does not have 12V with the ignition fully on. So, I am now headed to the interior heat lever switches. Once I figure out how to get to them. :-)

[Monza_dh]

why not do the infamous heater bypass route? do a search and you find many links for removing the blower and just using your footwell blowers. it will look like this:

[Chris Lovell]

Monza, this sounds like a really good idea and for $35 and a six pack of PBR, a bargain. My problem is the footwell blowers also do not work. I was thinking those will only work if the engine blower is working. Is there a work around to enable the footwell blowers only?

[wdfifteen]

Originally Posted by Chris Lovell

Monza, this sounds like a really good idea and for $35 and a six pack of PBR, a bargain. My problem is the footwell blowers also do not work. I was thinking those will only work if the engine blower is working. Is there a work around to enable the footwell blowers only?

I am very interested in hearing an answer to this. My footwell blowers don't get power to their fuses under any circumstances. If I could find a way to make the floor levers power the blowers I'd get rid of my engine compartment blower. Right now it's the only one that works.

[Chris Lovell]

bump. Patrick and I are interested.

[aj88cab]

Grab a beer (or two) and start reading

Start with this to get an overall idea how the control circuit works:
Heater Control Circuit

And this:
http://members.rennlist.com/imcarthur/911autoheat.htm

Then this one that discusses a "jumper mod" that will delete the engine blower and allow you to use the footwell blowers (read to end for latest mod variation that eliminates the FW blowers running all the time):
Carrera - Removing Engine Compartment Heater Blower


There are several other threads that address this item too. Just search "engine blower" or Jumper mod", etc.

[Chris Lovell]

Man o man, Andrew to the rescue again!!! Thanks. I think the beer is the best idea.

[Chris Lovell]

Andrew and all,
Even though Pin 9 did not have elec power with the heat levers up, it turns out the relay was the problem. I tested the heat lever microswitch for proper operation and it is fine. I then swapped the relay with 86 911 and the heater blower works fine. So, thanks for the help and guidance. Now on to the next project.
Anyone know a good source for the 918 618 153 00 relay?
CL