Ceramic block 1988 300E
 

Hi all,
Can anyone tell me what this is? It looks like a ceramic fuse.
It's behind the L/F head light.

Thanks,
Greg

Think that is the ignition coil resistor.

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Doh ! :rolleyes: Just looked at the '92 in here...coil type resistor...ie, the resistor is a few coils of wire mounted on the ceramic holder for the fans.

I'm claiming temporary insanity ! :rolleyes2

Electronic ignitions don't have ballast resistors like old point ignitions, though that's what it looks like.

It's the electric fan resistor - it's required for two speed operation. At low speed the resistor cuts voltage to the fan for lower speed.

Duke

Thanks for responding to my? Looks like its time for a new one.
Will it keep the aux fan from turning on?

I don't think it will stop the auxiliary fan from coming on when your engine gets too hot. It only prevents the fan from coming on when necessary for your a/c. replace anyway, it is pretty cheap, and real easy to fix.

I just looked it up on fastlane, $24.00 for the part. I just picked up the car
two weeks ago, and have not had the time to look at it till today.

Greg.

Just finished refurbing my fan systems so this is all pretty fresh. It works like this:

The fan resistor cuts the current to the auxiliary fan so it runs at reduced speed when activated by the AC system pressure switch.

If you want to check it's working correctly, start engine and turn on AC. Once pressure builds up in the system, the aux fan should come on. Jump the two terminals on the resistor with a piece of cable and the fan should run at a higher speed.

If its blown, i.e melted, you'll possibly find the fan doesn't come on at all unless you jump the terminals. If the fan isn't working and doesn't come on when you jump the terminals, suspect the AC pressure switch. It is red, plugs into the AC line and has two terminals. If you jump the two connectors the fan should start.

When the engine temperature switch registers 87 deg, the fan gets full current through a different circuit and runs at high (full) speed. I didn't investigate this process, other than changing the temp sensor, but I think I'm right in saying it's entirely independent of the AC switching circuit.

Hope this helps

The electric fan doesn't engage at high speed until about 105C coolant temperature.

To check the resistor, just test for continuity with the ignition off.

The resistor cuts voltage at the fan, which reduces current and causes the fan to run at lower speed that if full system voltage is applied.

Duke

Oh yes they dooooohooo !! :D :D Nah na na nar narh....
http://www.slantsix.org/articles/elect_ign_wiring/elect_ign_wiring.htm

i stand corrected.

Aux fan first stage starts at 16 bar and stops at 11 bar pressure in the AC system, second stage starts at 107 deg C and stops at 100 deg C

Thermostat starts to open at 85-89 deg C and is fully open at 102 deg C

Mind you, seeing as I live in the tropics and rarely get out of town, I run an 85 deg temp sensor to kick the fan in early if I'm stuck in traffic. Hence the confusion.

Full temp switching specs are here if anyone's interested.

85C Switch
 

Sorry to ressurect old post, but I am also in the tropics (Malaysia) with a 'hot' 124.

Simmo, could you provide info in the 85C switch that you used to get the high speed aux fans going? Is it plumbed into the cylinder head (kinda midway lengthwise, between cam cover and airbox) with a blue connector?

Cheers,

P.

sounds like it. its a single post connector, second from the front, so about level with cylinder 2/3.

mine didn't have anything connected to it originally so I have no idea what its supposed to be used for but my mechanic ran a connector and cable from it back to the fuse box and spliced it into the sensor feed going into the high speed fan relay, thereby bringing the fan in early at 85deg. I think it actually cuts in just over 80 deg.

since my cooling system is now up to scratch and I know the high temp sensor is working, I disconnected it because I was worried about the engine not getting up to operating temp and out of warm up enrichment, which i think was more to do with a bad fuel distributor than irrational fears about the engine not warming up. have now changed the fd and stopped worrying about that.

anyway, because I was bored, I reconnected the cable and wired up a red push button switch into an available hole in my dash fascia so I can switch the fan to high speed if I ever feel the need in traffic.

bwaaahhaahaaaa

Simmo,

Thanks for the super quick response. The connector I was referencing on my engine actually has 2 pins, and in my case is connected to the harness. If I disconnect it, the high speed circuit is activated. I am almost decided to do a DIY cool harness thing (i.e. soldering on a suitable resistor) to reduce the activation temp from 115C to 92C.

Well, that's the theory anyway. I like the button thing though :D

Cheers,

P.

that's the correct sensor for the high speed which trips it at 107 i believe. just in front of that should be the single pin I'm talking about. As I said, there was nothing connected to that on my engine so I'm not sure what its there for.