74 3.0 CS wiring help

m5bb

m5bb

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Ok, started this in another section but title needed to be more specific
74's seem to be different than say a 72.

This car has issues with starting and running then when warm starting and dying.
Does anyone have a wiring diagram that also shows the AC circuits.
The diagram (multi colored) only shows main circuits and does not show the relay for the aux fan that comes on with AC on.

The relay that I have found that is running this is the first relay to the front of the car next to the battery. Different than a 72.
I believe a PO or shop tried to wire the aux fan so it comes on with key on regardless of AC or temp.
When the relay is installed it is hot and I mean it is on regardless of the key. This is why the battery is going dead.

To the right of this relay is the horn relay. Tested. To the right of that #3 relay I'm not sure what it is for. Still trying to determine.
Where the voltage regulator is on most cars and this car the high beam relay is below that. Kind of hidden. See photo.

Then I found and tested three more relays above hood release arm under dash.
Found two of those are not working. That was at 10PM tonight so decided to stop.

So any diagram would be helpful and will get back on it in the morning.
Had a couple more photos but forum won't load any more. Maybe there is a total file size limit?
 

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The Blue Binders have a good 74 wiring diagram, the color ones on eBay are too generic. The fan was never driven by a relay near battery, I would disconnect it. That fan is switched from the A/C panel, the fan switch in particular and relay is near coil as Steve posted. The 74 near the battery has horn, high beam and low beam (first time they were added) relays. See page 61-0/48 and 49, it's euro configuration with city lights, etc, but should help.
 
Chris, I will check that.
I see no evidence that the relay was near the coil?

The wires from the aux fan go across above the radiator and are wrapped just like a factory wire would be and come through the bulkhead right in front of the battery. I see no evidence that they are not original.

Also 2 wires connected from the temp sensor unit at the bottom of the radiator.
There was also a diode in the wire from the compressor that goes to the off/on switch in the dash. It was shot and struggling to understand it's purpose?

Could be to protect the dash AC switch from spikes from the compressor clutch when it cycles off and on.
 
Gary - some comments:

Have you checked the battery? The constsnt drain to low voltage may have damaged it.

There is no reason to install a relay in a circuit that is always hot. Moreover, relays are usually used on items with larger current draw, and it is again odd to have a high draw item always hot. That circuit seems to be a problem.

Can you follow the fan wiring and determine specifically how it is wired?

You mention a/c a lot. Does the car run ok if the a/c is off?
 
HB Chris said:
The 74 must be different. My 73 never had temp sensor in the Radiator. Can another 74 owner confirm?
Click to expand...

Here is a picture of the sensor on my 74 if this is the one you are talking about.
 

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My 74, with AC, has no temp sensor. The wiring on our beloved cars seems to be as variable as the location of side-view mirrors, radio antennae, and side-marker lights...
Dec 2016 update: I was wrong...PO disconnected the AC and removed the temp sensor, replaced it with a threaded plug, and I didn't notice that until recently.
 
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BTW- the BLUE manuals have so much information.
I guess I don't look there soon enough.

There are pages of wiring diagrams and a whole page devoted to the AC wiring circuits.

Thanks Chris M. for reminding me to look there.
 
Here is the radiator mounted temp sensor.
Says 1/73-11/75

61311364272 TEMPERATURE SWITCH - 91CEL (10/73 to 11/75)


And here's another mystery. See photo.

A diode in the line from the AC dash off/on switch to the AC compressor.
On both cars.
Shown in parts and still available.
Not sure of purpose other than to prevent spikes from compressor getting to switch or fan?
 

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Never seen one of those either. I was surprised that that hot wire from the switch goes to relay for the fan only, the compressor gets power direct from the input spade on the relay, not from the relay.
 
If you have a sensor that turns on the aux fan when the car gets hot and the AC runs the low speed fan to cool the condenser- you better have a diode in the circuit or every time the car gets hot it will activate the compressor. You can use a relay with 87 and 87a from the AC or two relays or a diode... You just don't want to make heat when you are overheated!
 
sfdon said:
If you have a sensor that turns on the aux fan when the car gets hot and the AC runs the low speed fan to cool the condenser- you better have a diode in the circuit or every time the car gets hot it will activate the compressor. You can use a relay with 87 and 87a from the AC or two relays or a diode... You just don't want to make heat when you are overheated!
Click to expand...

I think I see this.
But the aux fan is common to both operations.
Turn on AC and aux fan comes on.

AC off but car gets warm, aux fan turns on.

"every time the car gets hot it will activate the compressor" and the aux fan?

Not sure what low speed fan you mean other than evaporator fan in car?

Don,
Any suggestions on two relays that are +12v with key off.
1. Relay for aux fan
2. Load shedding relay above hood release arm.

Key seems to test ok. 12v at coil and turns off and on. Activates starter.

I'm stuck........
 
My bad for not being clearer..

Aux fan (low speed) is used by AC and by cooling system when engine gets too warm.

Turn on AC and aux fan goes on to cool condenser.
Engine gets hot and radiator temp sensor turns on aux fan.

Both operate by sending +12 volts signal to a relay that operates the aux fan.

Problem is if they share the same pin on the relay the hot engine sensor will backfeed to the AC compressor turning it on and make things worse.

You can use a diode to stop this or a 5 pin relay or 2 four pin relays. Lots of ways to do it.

What other relays are hot? Euro window relays are hot with the door open.
Try again with the door shut.
Test for amps with key off.
 
sfdon said:
My bad for not being clearer..

Aux fan (low speed) is used by AC and by cooling system when engine gets too warm.

Turn on AC and aux fan goes on to cool condenser.
Engine gets hot and radiator temp sensor turns on aux fan.

Both operate by sending +12 volts signal to a relay that operates the aux fan.

Problem is if they share the same pin on the relay the hot engine sensor will backfeed to the AC compressor turning it on and make things worse.

You can use a diode to stop this or a 5 pin relay or 2 four pin relays. Lots of ways to do it.

What other relays are hot? Euro window relays are hot with the door open.
Try again with the door shut.
Test for amps with key off.
Click to expand...

Got it and makes sense.
Not a euro car. But yes door was open. Will check that.
Haven't tested amp draw mostly because I know the battery goes down in a day or so.
You still say "low speed" aux fan. Is that fan two speeds? If so I'm not seeing it?

I'm just not sure if something has been changed. At one point I think someone wired car so aux fan was on all the time. I understand why they would do that but probably not necessary if everything else is working correctly.
I checked all AC wiring according to drawing in blue book. Checks out ok.
One thing I did notice yesterday is that I had to replace AC thermostat control switch. One with capillary tube going to evaporator.
BMW part NLA so got switch from Vintage air. First it fits in location and has same two pins for wiring. Same manufacturer as original. Best I could determine it was rated the same. Small problem was the chrome bezel ring from original is metric and this one US. I was able to rethread enough of the shaft to get the original chrome ring on.
But I did notice that both switches, on/off/fan speed and temp control are turning on aux fan. Car is not running but doubt it would change.
Not sure why this switch is different than original? I bought two so will go back and look at that.
To many places to chase???
And taking the center console apart is such a pain.

Thanks for your help Don.
Gary
 
The replacement switch has an off position, don't think original did, I have same switch, have to turn both on or just leave temp switch on all the time and use fan switch to energize. I couldn't find a bezel either, thread is Very Fine, not just Fine. Looks like Blaupunkt bezel but isn't that either.
 
Ouch - low speed fan is bad, left over when I worked on 80's cars.
I always install 2 speed later fans now on the e9's so I think of low speed still.
You can always call me.
 
Ok, Don and everyone here is the latest.

After many hours and help from my brother we could not find anything that was shorted or bad ground etc. etc.

Kept looking at relay for Aux fan and how it was wired.
As I said previously I believe a past owner or mechanic set up this car so the aux fan turned on with the key. That's what the current owner has told me a couple times.

We decided to move the pins around in the connector for the relay like the circuit and wiring diagram showed they should be.
The way it was wired the relay would be on all the time.
Viola, this seemed to straighten out the always on situation with the auxfan/AC relay.
Everything worked like I believe it should.

We still have a load shedding/ changeover relay that is on all the time.
Have gone through the wiring for the key twice and haven't figured this one out yet.
I found another one of the diodes (like the photo I posted earlier) in a line that is part of a main harness and near the fuses.
Haven't traced this out yet.
Amazingly this relay is not fused by any of the fuse box fuses.
If there is another fuse I have not found it yet?

Nice 48k mile car.
Not mine.
 

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