93 Mercedes 300te m104 fans not coming on

[Shawnb]

My fans are now not coming on. Fuse looks good.

With or without the AC, they don’t come on and the temp will start to creep in traffic. It’s fine when moving. This just started to occur today.


Anyone have any ideas?


Thanks

[tjts1]

Fans are supposed to turn on at 105-115c. What temp did u see?

[Zulfiqar]

Originally Posted by Shawnb

My fans are now not coming on. Fuse looks good.

With or without the AC, they don’t come on and the temp will start to creep in traffic. It’s fine when moving. This just started to occur today.


Anyone have any ideas?


Thanks

there are 2 relays in the fuse box, one blue and one green and both have fuses in them, blue is slow, green is fast. Check there.

if all is good, and no dice, remove fan connector at inner corner of radiator shroud and test with test lamp - you can even use a couple of wires to supply that connector with power to see if the fans kick on.

If all is good - check the resistor bolted next to the reciever dryer and the ABS pump right behind the driver headlamp. wiggle the wires on it and see if they are charred to dust.

If they are - then replace the resistor and crimp on some new eyelet lugs to the wiring and screw down to the resistor,

The fans should now work properly.

When the resistor fails bad enough it will fry even the high speed wiring.

[Shawnb]

Originally Posted by Zulfiqar

there are 2 relays in the fuse box, one blue and one green and both have fuses in them, blue is slow, green is fast. Check there.

if all is good, and no dice, remove fan connector at inner corner of radiator shroud and test with test lamp - you can even use a couple of wires to supply that connector with power to see if the fans kick on.

If all is good - check the resistor bolted next to the reciever dryer and the ABS pump right behind the driver headlamp. wiggle the wires on it and see if they are charred to dust.

If they are - then replace the resistor and crimp on some new eyelet lugs to the wiring and screw down to the resistor,

The fans should now work properly.

When the resistor fails bad enough it will fry even the high speed wiring.

Lots of info, thanks!

The fuses are unlike any I’ve ever seen. Weird tiny ones, with just metal strips. None appear to be blown. Is there another fuse panel? This one is right near the drivers strut hat.

Neither fans work. The car didn’t get near the red zone, but it was climbing that way in traffic, and luckily there was room to start moving again and all was fine on my hour ride home. Just in 5+ mins of dead stop traffic did this occur. I drive this car a lot and the fans are usually rather loud, when stuck in long traffic.

Can’t get them to work with AC on or off. I’ve also always had cold air. Earlier today the AC was blowing warm for 2mins, and I just rolled down the windows thinking there’s probably a leak in the system. On my ride home the AC was back to normal. Weird.

[Zulfiqar]

Originally Posted by Shawnb

Lots of info, thanks!

The fuses are unlike any I’ve ever seen. Weird tiny ones, with just metal strips. None appear to be blown. Is there another fuse panel? This one is right near the drivers strut hat.

Neither fans work. The car didn’t get near the red zone, but it was climbing that way in traffic, and luckily there was room to start moving again and all was fine on my hour ride home. Just in 5+ mins of dead stop traffic did this occur. I drive this car a lot and the fans are usually rather loud, when stuck in long traffic.

Can’t get them to work with AC on or off. I’ve also always had cold air. Earlier today the AC was blowing warm for 2mins, and I just rolled down the windows thinking there’s probably a leak in the system. On my ride home the AC was back to normal. Weird.

The relays are not in the flip top fuse box, its in the box right behind it, to get to it raise the hood vertical (service position) and then unscrew the top of the box, you will see a bunch of relays there and in those relays will be tiny regular blade fuses. (the blue and green relays for the fan are side by side closer to the fender)

btw - your engine should never heat up to danger point even if the condenser fans are off, the main engine fan should be working pretty strong with hot ambient temp and A/C running. (you will hear it roar like a garbage truck or school bus)

If its not roaring - the fan clutch is probably dead, and needs to be replaced/refilled.

[Arthur Dalton]

Bring a jumper wire from bat + to the resistor behind l/headlamp. Key OFF

Touch one side for low fan , the other for high.If YES, then the problem is upstream from Resistor.

Jumper the sw at drier that has the 2 6" pigtail wires .
That is low fan.
If yes, sw. is bad or a/c system is low on refrigerant.
Key ON

Unplug blue 2 wire coolant temp sensor w/key ON, this will get high fan.

Report findings

[Shawnb]

The fans not coming on and the wonky AC issue are related. Both happened at the same time.

In the morning the AC could blow hot air, but later in the day it will work. System is not low, I have gauges.

[Arthur Dalton]

Fine.

[Shawnb]

Originally Posted by Arthur Dalton

Bring a jumper wire from bat + to the resistor behind l/headlamp. Key OFF

Touch one side for low fan , the other for high.If YES, then the problem is upstream from Resistor.

Jumper the sw at drier that has the 2 6" pigtail wires .
That is low fan.
If yes, sw. is bad or a/c system is low on refrigerant.
Key ON

Unplug blue 2 wire coolant temp sensor w/key ON, this will get high fan.

Report findings

Somehow glanced over this.

I will give this a shot

[MCallahan]

My M103 is getting hot at a stop, too. No time at the moment to fix it (going to swap fan clutch and HS relay from parts car tomorrow), but have been able to keep temp in check by running heater full blast (max temp on the wheel and max blower). Old school trick, but it works. Car is fine on the highway and AC is working great, but temp starts rising when you stop.

[Zulfiqar]

Originally Posted by MCallahan

My M103 is getting hot at a stop, too. No time at the moment to fix it (going to swap fan clutch and HS relay from parts car tomorrow), but have been able to keep temp in check by running heater full blast (max temp on the wheel and max blower). Old school trick, but it works. Car is fine on the highway and AC is working great, but temp starts rising when you stop.

swapping in a HS relay wont help if the wiring is burnt on the resistor.

Arthur's post above has one very important piece - remove the blue coolant sensor connector to cause the HVAC module to kick start the fans to full speed immediately when the key is switched on. That test basically gives you the quickest way to confirmation of the wiring. e.g. if fans dont start, use a test lamp to see where the power is missing.

e.g. resistor leg, relay fuse, etc.

[Shawnb]

Originally Posted by Zulfiqar

swapping in a HS relay wont help if the wiring is burnt on the resistor.

Arthur's post above has one very important piece - remove the blue coolant sensor connector to cause the HVAC module to kick start the fans to full speed immediately when the key is switched on. That test basically gives you the quickest way to confirmation of the wiring. e.g. if fans dont start, use a test lamp to see where the power is missing.

e.g. resistor leg, relay fuse, etc.

Where is the blue coolant sensor on the wagon?

[Shawnb]

With the blue coolant sensor disconnected. Nothing happens.

Which fuse should I be looking at? No idea how to tell when these are bad

[Zulfiqar]

Originally Posted by Shawnb

With the blue coolant sensor disconnected. Nothing happens.

Which fuse should I be looking at? No idea how to tell when these are bad

Now that you have it disconnected.
test for power at the fan connector or resistor leg out (this is where the wiring for high speed is spliced.) If you dont find power at all at the resistor leg too then trace back to the High speed relay which is in the relay box right behind the main fuse box (the relay box has screws to remove the cap unlike the fuse box) - raise hood to vertical first.

[Shawnb]

Originally Posted by Zulfiqar

Now that you have it disconnected.
test for power at the fan connector or resistor leg out (this is where the wiring for high speed is spliced.) If you dont find power at all at the resistor leg too then trace back to the High speed relay which is in the relay box right behind the main fuse box (the relay box has screws to remove the cap unlike the fuse box) - raise hood to vertical first.

The photo above is the relay box. Unsure of which is for the fans though