1972 280SE 4.5 Cooling - Page 4 - PeachParts Mercedes-Benz Forum

Arthur Dalton · #46 07-19-2009, 07:48 PM

If it is double pole relay , then someone may have used the other pole to drop ac clutch if temp sensor grounds and calls for aux fan to keep coolant temp in check

That is a possible Mod.

But whatever was done, you want that aux fan to work at 100C regardless of anything b/c those 4.5's can run hot.......
even if it means a mod with another sensor.

My question is where does the schematic show the 100c sesnor get fed from ?

rkroel · #47 07-19-2009, 08:39 PM

Sorry, I should have said double throw relay, not double pole. I'll correct that.

The schematic shows the 100C sensor as a grounding switch for pin 85 of the aux fan relay. The coil and the switching for the aux fan relay are both fed from the same aux fuse box which is in turn fed from fuse #2 in the main fuse box.

The coil of the double throw relay in the schematics is fed from pin 50 of the starter and the contact is fed from the temperature switch.

I'm going to see if the aux fan kicks in when the car gets hot (with the ac off) now that I have cleaned the relay up.

If that doesn't work then for now I'm going to jumper the dryer temperature sensor so that the aux fan comes on with the ignition.

Arthur Dalton · #48 07-19-2009, 08:54 PM

Quote:

Originally Posted by rkroel

Sorry, I should have said double throw relay, not double pole. I'll correct that.

I knew that..the meaning was the point.

The schematic shows the 100C sensor as a grounding switch for pin 85 of the aux fan relay. The coil and the switching for the aux fan relay are both fed from the same aux fuse box which is in turn fed from fuse #2 in the main fuse box.

Ok..So, that simply means that both the coil and contactor set are using the same fuse feed as common 12v and once that 100c grounds the coil side of the relay, the fan should come ON if the fan is fed from 87 of that relay.

The coil of the double throw relay in the schematics is fed from pin 50 of the starter and the contact is fed from the temperature switch.

Now that is strage..Benz circuits 5O are starter crank position. They must want no a/c mag when cranking.

I'm going to see if the aux fan kicks in when the car gets hot (with the ac off) now that I have cleaned the relay up.

If that doesn't work then for now I'm going to jumper the dryer temperature sensor so that the aux fan comes on with the ignition.

OK

Why did the other relay click when you ground 100c sesnor is a good question?

rkroel · #49 07-19-2009, 10:15 PM

Just took it for a test spin. It is a little bit cooler out than my last test drive. About 108 right now.

I was able to drive around for 20 minutes with the A/C blowing full tilt with significantly less gauge movement. The gauge still climbed very slightly at stop lights. The needle stayed right at 3/4 until I pulled in my driveway and idled for about 5 minutes. The needled move slightly above 3/4 at this point but seemed to be holding.

So, we have more progress.

Arthur Dalton · #50 07-19-2009, 10:19 PM

Is that with drier jumpered ?

rkroel · #51 07-19-2009, 11:11 PM

Quote:

Originally Posted by Arthur Dalton

OK

Why did the other relay click when you ground 100c sesnor is a good question?

If you mean one I circled in yellow, it's because I'm an idiot - it wasn't actually clicking.

Before I cleaned the contacts on the relays it was a bit intermittent, so I pulled the yellow circled one and the clicking stopped. So I thought.

rkroel · #52 07-19-2009, 11:11 PM

Yep, that was with it jumpered.

Dinner was ready when I got home so I didn't have a chance to hook the dryer switch back up.

Arthur Dalton · #53 07-20-2009, 05:13 AM

Quote:

Originally Posted by rkroel

If you mean one I circled in yellow, it's because I'm an idiot - it wasn't actually clicking.

Before I cleaned the contacts on the relays it was a bit intermittent, so I pulled the yellow circled one and the clicking stopped. So I thought.

Oh.. Ok. That explains it . Had me goin' on that one.

Well.... it seems you are getting it squared away now.

rkroel · #54 07-20-2009, 11:29 AM

Hah, sorry about that.

Drove ~30 miles into work this morning in 90 degree temperatures. The needle stayed just below 3/4 untill I hit the parking lot. Never went past the 3/4 mark though.

Thanks again.

Arthur Dalton · #55 07-20-2009, 11:43 AM

You're Welcome.........

evoldeal · #56 07-20-2009, 03:25 PM

Quote:

Originally Posted by Arthur Dalton

Yes . they do ...but it is b/c they do not have the TWO fan circuits like Benz does.

So, guys who know the old Benzs all put a cabin sw across the drier so they can get a fan going ANYTIME they see fit , be it traffic, Towing ,long idle, working on the car , etc...it is a simple OVER-RIDE modification using the drier sw as the point of jumping w/cabin sw. Nothing changes in the Factory wiring, you are simply by-passing the sw for MANUAL fan. And all factory relays and fuses are still being used..you are simply by-passing the factory circuits sensor..a GOOD $5 modification w/o screwing up any of the orig circuitry...... no other parts requires b/c you are using what is already there.

I have been having the same problem with the needle spiking in NYC traffic a couple times the past few days on my new car. I don't have A/C. It only gets up to about the 10 o'clock position on the dial, apparently not in the danger zone. But enough to make me nervous while sitting in hot summer traffic

I took it a mechanic to have it all looked over this morning, and I mentioned the above solution from Arthur Dalton. Mechanic just waved his hand and said I didn't need it, and that the fan comes on by itself at 212F.

I tried pushing the point, but he wasn't really having it. oh well, I liked the idea of having that switch to use as needed.

Arthur Dalton · #57 07-20-2009, 03:35 PM

< oh well, I liked the idea of having that switch to use as needed. >

B/C you have no ac , yours is a simple mod for manual sw.
Just take a wire from that coolant 100C sw and bring it into the cabin to a toggle sw ...then ground the other side of the toggle under the dash.
You now have a Manual Over-Ride fan control to have anytime you want it..nice for towing,traffic,etc.
This does not open a can of worms with the stock set-up b/c when you are not using it , the cars fan circuit goes right back to Fact Orig. [ just to keep yor mechanic happy]

Mike D · #58 07-20-2009, 04:47 PM

And the beauty about doing it as Arthur suggests is the worst that could happen would be if the wire rubbed bare it would simply engage the fan and not blow any fuses/relays.

Arthur Dalton · #59 07-20-2009, 04:55 PM

Yup... Then YOU are the sensor...and you are a BETTER sensor b/c you can be a Variable temp sensor......

I did one for a customer years ago and he loved the Roar of the fan ..so the idiot would pull into any place where people were looking and he would hit the fan just to get that rush of thinking he was cool.
Those old single fans did have a kinda jet turbine sound to them....

rkroel · #60 08-06-2009, 02:48 AM

A quick update.

The car still doesn't like to cruise at 75 or 80 with the A/C on in the heat of the day. I still find myself turning the A/C off in heavy traffic.

The aux fan has been somewhat intermittent, it requires a fuse spin occasionally. I'm going to thoroughly clean all the fuse boxes and relay contacts in the car.

My next step is to flush the coolant, replace the thermostat and refill with distilled water and water wetter.

If the car still doesn't cool well enough the radiator is up next. It does not appear that there is room for a wider, or thicker radiator without removing the engine oil cooler.

I don't like the idea of removing the oil cooler. However modern motor oils are much less prone to coking. It might be worth some investigation with an oil temperature gauge, if I can find the operating oil temperature range in my manuals somewhere.

Any thoughts?