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  #1  
Old 06-15-2003, 11:16 PM
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Arthur Dalton - here are some more pieces to my puzzle...

First of all, I want to thank you for all the help on my last thread about the aux. fans on my '90 300CE. See: basics checked, but w124 fans still not working

Problem is, things still aren't quite right. After a lot of testing, cleaning contacts, etc., I discovered:

1) that my relays and fuses are fine,

2) that the plug where the aux. fan harness from the fusebox and the harness from the fans plug together (right next to the receiver-drier) has either a bad connection or a bad wire (this was the real problem), and

3) something is stilly fishy with the drop resistor and coolant temperature sensor.

Here's the issue: when I bypass the drop resistor, BOTH fans will work when I jump the a/c pressure switch. They both work whether the coolant temp switch is connected or not. This seems strange. If I re-connect the drop resistor only the a/c fan (passenger side) works. If I re-connect the drop resistor, the driver's side fan does not work, but the passenger side will work as designed - when the a/c switch is hooked up and the a/c is on.

Bottom line is, I think my drop resistor is bad because the driver's side fan doesn't run when the reistor is hooked up, but I'm still baffled as to why the coolant temp switch didn't seem to have any affect on things?

My other question is whether the a/c switch works on varying pressures. Is it possible that there is enough pressure to engage the a/c fan but not the coolant temperature fan?


Thanks,

GregS
'84 300D, 174k
'90 300CE, 164k
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  #2  
Old 06-15-2003, 11:58 PM
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Location: Florida / N.H.
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<< that the plug where the aux. fan harness from the fusebox and the harness from the fans plug together (right next to the receiver-drier) has either a bad connection or a bad wire (this was the real problem), and

3) something is stilly fishy with the drop resistor and coolant temperature sensor.

Here's the issue: when I bypass the drop resistor, BOTH fans will work when I jump the a/c pressure switch. They both work whether the coolant temp switch is connected or not. This seems strange>>
Nothing strange there , that is Normal

You have some conflicting info here, but I will try to expalin the basics

The Resistor is to lower the voltage to the fans when the a/c pressure sw is activated by a/c high side pressure or jumpered..
If you jumper the resistor AND the a/c pressure sw, you will have HIGH fan [ both fans, at high speed ].. If you then remove the resistor jumper , you will have LOW fan [ b/c the resistor is now in the circuit and dropping the voltage to the fans]... if you now have no fan , you have a BAD resistor/connection at resistor...
Do not confuse the resistor circuit with engine coolant sensor circuit ,, these two circuits have NOTHING to do with one another .. they only SHARE the same fan motors at the end of each circuit.
The ECT circuit is HIGH fan ONLY, and does not use the RESISTOR..or, for that matter, the a/c sw or relay..
The fans are wired in Parellel, so they work in unison... if you see some bad wiring at the connector that you mentioned , it is possible you have incorrect wiring there and even possible series hook-up..

It is hard to visualize these two circuits , but if you could see a schematic, you would plainly see how the two feeds come to the common fan motors..
Do you have a schematic, by chance??
Email me offline and I can walk you through it..
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  #3  
Old 06-16-2003, 12:11 AM
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Unfortunately I don't have a schematic. From what you are saying, when I jump the a/c switch AND bypass the resistor, what I have is both fans running at high speed. The coolant temp switch should work when I disconnect the switch on top of the thermostat housing (remember, I have CIS-E injection). Therefore, it seems like the a/c circuit is working, but the high speed cooling circuit is not. Perhaps the coolant relay is broken. On my car the relays for the a/c circuit and the coolant circuit are different (you can't switch them to see if one works in the other socket), so even though I can hear the relays clicking, maybe the coolant circuit is bad.

So how about this: I just bypass the the drop resistor completely. This way, I know that when the a/c switch trips, both fans will engage and they will be running at high speed, and I don't have to worry about when or if my coolant circuit will kick in.

It was only 80 degrees today, and with the a/c on, sitting in traffic, my temperature was half way between 100 and 120 degrees. I know some say this normal, but my diesel never, ever goes above 95 degrees, so these temperatures make me very nervous.

This little modification seems like a decent solution to the high engine temperature issue on this car, especially since I can't do the mod possible on cars with latter fuel injection.

GregS
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  #4  
Old 06-16-2003, 12:37 AM
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Location: Florida / N.H.
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<>

Very possible.
What you want to do is check the ECT sensors resistance values.
That feeds the ACC push button control unit, which in turn , trips the coil side of the aux fan relay to complete the HIGH FAN circuit..

The ECT sensor trips at 105/107 and that is high fan [ both]
This circuit is also fused on the load side of the relay , so if you don't have high fan I would check that fuse first..or the connection at the resistor [ both circuits use a common terminal
at the resistor , even though the High fan does not use resistor]
This will be the two wire side of resistor.
I would look into the ECT circuit before just jumping the resistor and expecting that to cool high eng coolant temps , as
these fans will still not come on until the high side pressure on a/c is tripped...
You definately want BOTH systems working...
I can send you the schematic...
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  #5  
Old 06-16-2003, 10:58 AM
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Arthur, when I unplug the ECT, I can hear the relay clicking, so I suppose that circuit is doing something. But to be thorough, I really need to check this circuit again now that the harness connection is working. All fuses are in good condition.

Thanks again.

GregS
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  #6  
Old 06-16-2003, 11:05 AM
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Posts: 459
Regarding the ECT - to test this circuit, am I supposed to just unplug it, or jump the connection?

Also, is it safe to assume that the drop resistor is working properly if the low speed fans works with the a/c on?

Thanks,

Greg
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  #7  
Old 06-16-2003, 11:11 AM
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Join Date: Aug 1999
Location: Florida / N.H.
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If you hear the relay clicking , then the sensor side of the circuit is working and pulling the relay in [ coil is being energized]
So, your problem is on the load side of the circuit.. that means contacts in relay or, more likely, load fuse for high fan.. Have you found a fuse for high fan??

I will send the schematic and then you will plainly see the load circuit...pretty simple, just some contacts in relay feeding the fan motors- no resistor in the circuit..
I personally think you have No power at realy contacts [load fuse]
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  #8  
Old 06-16-2003, 11:14 AM
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<
Thanks,
>>

Correct

Wait up til I scan the schematic .. I am at work on-line at the moment...
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  #9  
Old 06-16-2003, 11:36 AM
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Join Date: Aug 1999
Location: Florida / N.H.
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It is in your mailbox
Study it and then email me with any questions and I will point it out to you on the schematic
Notice there are 2 relays.. the left one [ in schematic] is labeled "K-10".. that is the low fan, a/c resistor circuit.
Notice that the power goes THROUGH the resistor to get to fan...
The right one is K-9... that is the high fan.. notice no resistor, just direct connection to fans...and then fans go to Ground to complete the circuit.. simple power circuit..

See the little coils in each relay ?? [ pins 4 and 5 ] that is the sensor circuit/pull-in coil .
See the load side switch in relays ?? [ pins 1 and 3] .. that is the contacts for the fan motor...those are closed when the coil pulls them shut..
SOOOO, if you hear relayy click in, you don't have a coil side /sensor problem....you have a LOAD side POWER problem...

Note that W on schematic is ground [ your neg side of circuit]
to complete the circuit power
Now, get to work...
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