A little help with this A/C relay for aux fan operation?
 

This relay was just removed from my 260E...I would LIKE to put it on my 300TE.

300TE stock: Currently the A/C aux fan does NOT turn on at low pressures, only medium to high pressures...

260E /w this relay: Aux fans kick on medium immediately when A/C is on.
I believe this was done by dealership...there is an MB sticker on radiator support (writing rubbed off), showing R134a retrofit (although I BACK-converted it to R12)...but nonetheless, I did not put this relay in myself and this isn't something that came from the factory, so SOMEONE put it in...

Since I drive the 300TE daily, I want to get this swapped over so it will be better for cooling for both myself and the engine.

I am stuck though because the two A/C systems are different...there is an extra wire on my 260E that I cannot see on the 300TE:
NOTE: the blue wire on the 260E comes from the A/C compressor harness, but the wire does not exist on the 300TE :confused:

Photos:

http://www.w124-zone.com/downloads/p.../ac/relay1.jpg

http://www.w124-zone.com/downloads/p.../ac/relay2.jpg

http://www.w124-zone.com/downloads/p.../ac/relay3.jpg

http://www.w124-zone.com/downloads/p.../ac/relay4.jpg

Looked up the above relay, and amazon states:
BOSCH STARTER RELAY 80-92 0-332-019150

I hope the above photo's make sense...because I don't have a clue what that blue wire is...its missing from my 300TE...I thought maybe its a wire that came off the main harness that goes into the A/C compressor, but nope, both cars have 3 wires going in, so what's that wire? What could it be for?

It looks like they bypassed the thermo-switch on the R/D with an simple switchover relay. When it sees +12v across pins 85 and 86, it closes the connection from pin 30 to pin 87.

I assume you mean temperature and not pressure on the 300TE fan operation.

In normal operation, the temp switch for the aux fan would be open, then the temps would rise and the switch would close and allow electricity to pass through to turn the fan on. With the relay, as soon as the compressor comes on, the relay closes and turns the fan on.

If yellow went to ground, that's probably 85 or 86 on the relay.
I'll guess and suggest the black wire goes to the upstream side of the R/D and normally sees +12 when the system is on. It will probably go to the 85 or 86 (whichever the yellow isn't).
If that's correct, when black gets +12, it'll close the relay and connect across from red to blue. Red would go to the "downstream" side of the R/D and tell your fan to turn on (I'll guess pin 87). But it needs something to say, so it probably gets +12 from the blue on pin 30. The blue on pin 30 was connected to the 260E. Is that wire in the 260E constant hot connected to the battery, or switched +12v with the ignition?

So you think that wire is either constant 12v or ignition 12v then?

Is it safe just to run an extra wire to battery or ignition and see if that works? I see no way of finding out where that blue wire goes since its part of the harness and I'd have to tear the intake manifold apart to see where it went...

That odd wire probably goes up the compressor control relay. When it gets +12 (to turn the compressor on) it closes the relay and connects the two wires, turning the fan onto low speed.

-J

Since I am no electrician, if I pop open the relay and take a photo, could we reverse-engineer it and find out for sure?

Just get a multi meter or test light. You could go down to the compressor too, just find the wire which gets +12 when the compressor is running.

One thing to double check... The wires which were going to the pressure switch go to pinns 87 and 30 on the relay, 86 is hooked to ground and the "Mystery wire" goes to 85?

That setup looks like it was probably from a fog light harness or something. The fuse can be eliminated (or changed for the lowest amp one you can find).

-J

It may be difficult for you to retrofit it into the 300TE unless you know relay and auto electric well. This is what I suspect has been done on the 260E.

1) The 'odd blue' wire is tapped off the compressor harness. It is energized with 12V whenever the compressor is turned on.

2) The 'odd blue' wire is fed into the relay pin 86, 85 to chassis ground to turn on the relay to 'jump' the high pressure switch.

3) pin 30 is tied to the one side of the high pressure switch, pin 87 is the other side.

Others can chime in. Good luck.

That would be my supposition, yes. The blue wire is probably either +12 from the battery, or +12 from some switched source.

It is possible that it could be run from the compressor, by I'd speculate that whoever wired it was cautious about overloading circuits and would be less likely to tap off the compressor pull-in wire.

As far as safely tracing it back, I'd put a meter on it to figure out how it's powered (steady +12, switched + 12, compressor switched +12) and then check those places. I'd look at the battery terminals, and near the fuse box and see if there's a blue wire.

There's no real need to open it up. Does it have a small diagram on the side? Or a set of numbers, eg; 85, 86, 87a, 87 and 30? If so, it's a basic relay. I did a search and came up with a replacement that says it supersedes yours, and it shows up as a basic relay so odds are high that it's nothing complex.

Look on the bottom of the relay and match up the numbers with the colors of the wire in the pics. ah-kay has suggested one possible wiring combo and I suggested a different one.

About the only benefit I could see to ah-kay's suggested wiring would be that the aux fan would also shut off under WOT, or whenever the compressor shut off.

A relay is not going to overload the compressor circuit. The blue line can't go to constant power... The fans would run all the time.


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According to the schematic, they changed the aux fan wiring from 87 to 88. In '87 it looks like the aux fan was slow speed at medium pressure and high speed at temps above 105. In 88 they re-routed hi-speed control to the aux fan controller.

Post the connections on the installed-relay and it should be easier to figure out.

If the trigger to close the relay is on the compressor circuit, I agree it wouldn't overload, but if the fan is on the compressor circuit it might. I can't really see a need for a separate fuse since I think everything is fused elsewhere. That was one other factor in thinking it was a separate circuit.

Having looked at the schematic, it looks like the installer is using this relay to trip the pressure relay. I didn't realize the pressure switch had a separate relay (low speed) in addition the temp relay (high speed)

If blue is off the compressor (he said compressor harness, so it might be the compressor or it might just be wrapped in the bundle) and goes to 85 or 86, and yellow (ground) goes to the other; then it'll close red and black whenever the compressor is switched on, and the fan will run at low speed.

So if that is the case between the model year changes, is there a different way that I can get the aux fans to turn on low as soon as I turn the A/C on?

You want to connect it up like this:

http://www.peachparts.com/shopforum/...1&d=1334244143

You can get the feed from the compressor on either at the Klima relay, or right at the compressor. The output is on pin 7 of the Kilma relay.

-J

Just thinking about it, would there be any consequences to running it on a switched +12v line and have it run all the time anyway?

I mean being in AZ, its pretty much hot all the time? Then during the winter I could simply remove that wire for the 2-3 months where it is actually cold?

That way I don't have to mess around with gutting klima wires etc. I could hook it up to the blower motor resistor on the driver strut mount since its ignition 12v...maybe throw a small toggle switch inline so no need to even disconnect it...just flick the switch and its back to stock settings for the winter?

I wouldn't have it run all the time. It's extra wear on the motor, extra load on the (too small) alternator, extra noise, etc.

If you just want it to run all the time just connect the two wires for the pressure switch. The fan will run anytime the key is on; no relay needed.

Who said anything about cutting wires? Just make a Y adapter for the plug on the compressor. Hmm, offhand I don't know what the connection for the clutch coil looks like.

-J

How competent are you with auto electric? There are simple hacks and there are better hacks.

1) Simple hack -Wire a toggle switch into the cabin to jump/connect the high pressure switch on the rec/drier. Toggle it when A/C is on. This will turn on the aux fan at slow speed thru the R14 ( may be R15, cannot remember ).

2) Another hack - Wire a toggle switch into the cabin to jump/connect 1 pin of the thermostat on the engine block to ground. Toggle it when A/C is on. This will turn on the aux fan at full speed.

3) Good hack - Splice into the compressor wiring or Kilma pin 7 to get a switched 12v. Then wire up what compu_85 drew. I also posted it earlier.

Good luck.

On my car this kills the AC... but I know the late cars are wired a bit differently.

-J

It is possible if the Kilma relay also monitors the switch setting. This is to simulate the 110C ( or 115C depending on the color of the thermostat ) coolant temp. It is does then ignore it.

On my late car there is no switch... there's the sensor in the water jacket for the ACC. It turns the fan onto high speed at 110*C and kills the AC at 120*C IIRC.

I'll review the W124 wiring diagrams when I get home.

-J

I believe this would work best because all I need is just the aux fan to run when the car is in traffic basically..
and I am not super competent at soldering in tight spaces etc...

Thanks guys

That's what I was going to do for A/C in the summer, even ran the wire into the cabin for the toggle switch....BUT I couldn't implement it so it's not an eye sore. Also the idea of having to turn it on/off manually, don't like it.

So what I did was replaced the coolant/aux fan temp switch with one that have lower temp trigger points.....now clutch/aux fan comes on sooner to cool the coolant/engine & also the A/C condenser. Also it's automatic, no toggle switch.

Why not a low cost kit based on radiator temp?

Derale Cooling Products 16769 - Derale Performance Adjustable Fan Controllers - Overview - SummitRacing.com

Depending on which app, it looks like you place a probe in the fins. I'd think the controller would be able to replace the high-pressure sensor and trigger the slow speed fan via a switched ground. If the controller only puts out a switched hot, then you can re-use the same type relay from the 260.

That's a nice temp switch! You could attach the sensing bulb to the R/D, have it kick on at like 120*F.

-J

I just redid my A/C with Envirosafe es-12 (yeah I know it's fuel refrigerant, sue me)

I set the low side pressure @43 PSI at idle, 1500 RPM about 35 PSI at 96 degrees ambient.

Not only does my AC kick ass now, a weird side effect- it also triggered the aux fans to kick on sooner than it did before. Yesterday car said it was 103F and I was still blowing 44F out of the vents according to my thermometer, and the car runs the AUX fan well before the tstat hits 87F.

moral of the story- increase your charge pressures slightly.

rjp

Moral of the story - KISS
 

The OP asked how to wire up the relay which we posted. He was not asking how to re-design the A/C system or replace the switch. Some MBZ switches at the rec/drier work on temp, some work on pressure. Some need to discharge the freon, some doesn't. I do not know what he has. He just wants a simple hack or instructions. Why make life complicated for OP?

The hack is simple and does the job. Keep It Simple Stupid.

Amazing. Like this is an acceptable solution? /\/\/\ Put a hole in the dash with a toggle switch?

How elegant :( Another dash ruined by backyard butchery.

How about giving the system enough pressure to register it needs to have the AUX fans on? Like it's supposed to?

To the OP. Spend a few bucks and increase the system pressure to the high side of spec- then go from there.

rjp


BTW "jumping" the high pressure switch on the reciever dryer also involves bypassing the pressure cutoff- you know that switch that registers when the system high side pressure exceeds 28 BAR it cuts off the compressor..Does the same when pressure drops below 2 BAR..

Its a safety feature.

Fiddling with that is a good way to blow your car to bits.

This thread reinforces what I'm saying - read Arthur Dalton's and the last post by SteveFL:

http://www.peachparts.com/shopforum/tech-help/66625-1991-300e-c-question.html

The cool harness mod would be ideal for your car...just one 1.1k ohm resistor involved.

I believe these are different pressure switches, or at least different pins on the same connector. There's the bi-function pressure switch that cuts off the compressor if the pressure is too low or too high, and there's this pressure switch that turns the aux fan on/off at moderate pressures.

Jumping the high pressure switch does not hurt anything. The overpressure cutoff is done by the low pressure switch.


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The cool harness mod is not what I need. I need to stop it getting to 100C point before the fans kick in. Out here when it hits 120F, its incredibly difficult to cool the engine down, its not a matter of fans turning on and it suddenly drops.

I need to make it so that it slows the rise.

So the cool harness mod is not what I need.

Also raising head pressures is the opposite of what I want. Increased head pressures increases condenser temperatures, which raises coolant temperatures, which raises condenser temperatures which lowers A/C cooling. Its a vicious cycle. Plus, I don't feel the need to contest with MB Engineering on pressures or reduce efficiency and longevity.

Just connect the two wires going to the pressure sensor together... the fan will run on low all the time.

-J

The thing is- increasing the head pressure in relation to the ambient temp (by increasing the charge) causes the AUX fan to kick on earlier. The AUX fan is both temp (by coolant temp) driven, and by high side system pressure. Raise one or the other and the AUX fan comes on. You won't be charging the system beyond spec, but to the maximum allowed.

Bypassing pressure switches isn't a good idea, either your compressor may die one day due to low freon (and you won't know it till it's too late) or you'll run the system till a barrier hose pops.

Read the thread I linked- note the mode of operation, and the fact those systems are properly charged by pros.

rjp

I'd recommend checking out the EPC startek site and looking at the wiring diagrams. You'd need to check the Aux fan section (there's a Table of Contents link) and the A/C section (it's not linked but it's in the back).

That'll help with understanding your specific car, since there's 3 or 4 variations in the gas W124s and the diesels are also different for what happens at which temp or pressure.

Then I'd look at the Summit Racing site and see if there's an easy low price kit that lets you replace the function of the pressure-switch for the aux fan with a temp sensor. These fan controller kits vary from mid $20 range to multi-hundred racing applications. The specific link I posted appears to be a cheap (maybe $30 IIRC) temp-programmable option that lets you place a probe in the radiator fins (no drilling or plumbing changes required).

In Arizona, I'd definitely look at an install that is ignition switched, eg, when the underhood temp is 140 F AND the ignition is on, then the Aux fan runs at least at low speed. I suspect that is easily and cheaply do-able with one of the Summit Racing kits. This type of mod should not affect any of the safety cut offs or function of the OE climate control.

This is an excellent idea... in fact to hook it up all you need to do is parallel the switch with the pressure sensor. Have something like this hooked up on my car:

https://lh4.googleusercontent.com/-u.../P00848600.jpg

I built an adapter harness which plugs between the sensor and the car harness, so no mods were needed for the car harness. If I ever decide to remove it I just unplug it.

Note the sensor with the 2 spades on the back is the too low / too high pressure cutout switch, which is wired in parallel with the compressor clutch. The red switch with the wires coming off of it with spades on the end is the 250PSI switch for the aux fan(s).

-J

Figured it out...Blue was as you guys said +12v source that went to Klima somewhere..

Ac relay working.MPG - YouTube

Now I will just bring the blue wire up into the dash somewhere discreet so not to ruin the dash or any interior by making horrible holes and voila!

Would you guys say its ok to use the blower motor resistor as my +12v source? I'd prefer not running another +12v wire across the engine.

You could use that, but it's on a really big fuse. I'd try to tie into something with a smaller fuse on it, like the radio power or dome light (which should be available at the buzzer relay)

-J

I'm not electrically savvy...what's the issue with having a big fuse? Is it in case of overload the fuse won't blow to protect the motor?

So the blower is on a 30 amp fuse. To blow the fuse you need to draw more than 30 amps. If the small wire going up to your relay shorted out it would probably melt / catch fire before it drew 30 amps of power. That's why you need to put the 12v source for your relay on a lower amp fuse, like the one for the dome light or radio, both of which are 8 amps in my car.

In your case you might just want to jumper the two wires going to the high pressure switch and have your fan run whenever the key is on. When it cools down in the fall you can simply return the wiring to stock.

-J

x2 This is the easier way to do it.

Since you have got the relay/fan going then why not go all the way and do it properly.

1) The blue wire is best go to a switched +12V at the compressor. You only want to turn the fan on when AC is called for. It may be difficult to splice into the compressor harness but it is not that difficult if you try.

2) Alternately, the relay only draws 10s of milli-amp. So it is possible to tap it off Pin 7 of the Kilma relay instead. Remove the kilma relay, insert a small gauge stranded wire into the Pin 7 hole and then push the Kilma back in. Then connect the small wire to the blue wire. You should be all set.

Now that I am this far, I may as well give myself full control over the fan.

Can I still use the blower motor resistor as my switched +12v source since the relay already has a fuse in it?

Do not understand what you meant by the blower motor resister as I am not familiar with W124 car. There should be no resister in the blower motor circuit as the speed is controlled by solid state electronics. Even if you could then the aux fan will run even when you only call for air, not A/C. I think we are beating a dead horse here as you know what to do to get it right.

Sorry, I mean blower strip fuse.

For those with a W124, what's the best way to route a wire from the klima relay to the driver side? Am I going to have to pull off all that engine shield foam to route the wire?

I struggle with soldering and cutting wires in tight spaces, so I really don't want to touch any of the factory wiring near the compressor for my own sake and make a real mess of it. Its nice and it works, I don't want any future issues because of my incompetence with splicing and cutting wires.

Here is my temporary solution until I can find a good way to access +12v compressor source. Runs all the time this way as soon as engine starts, but since I run the A/C all the time anyway in the summer, its no different in my case and if it cools down, all I gotta do is pop hood, flick switch and its back to stock settings.
I like the fact this solution has ZERO factory wires cut or spliced...nothing. If I take the relay out, its back to stock with no consequences :)

http://www.w124-zone.com/downloads/p...xfanswitch.jpg

Its mid 90's today so will be interesting to see any difference in A/C performance or engine cooling at idle. In 90F in traffic A/C on, my 79C thermostat will go up to about 85C, so I wonder if this extra airflow will keep it close to T-stat opening point now? :)

Robert, just wondering whether the wiring through the step resistor and on to the aux fan is sized adequately to have the fan running all the time. Seems to me I read that those wires are undersized for constant fan operation.

I have W126 300sdl. It was converted to 134 before I got it. Car runs cool on the road(82-83) if I stop it climbs to 105. The auxilliary fan never helps out. If I jump the wires at the dryer the auxillary fan cuts on immediately. I take it the dryer switch is not sending a closed circuit signal ever.

Since I am in FL and can use the extra cooling, whats the drawback with just jumping that circuit at the dryer?

Will the 105 high speed circuit, if it is working(I havent seen it that hot to test) continue to work as designed also?

thanks for info

There is a post on these forums where a guy doubled up the condensers on his W126 to convert to R134 - which solved all gripes.

but - if it matters, you can make the condenser fan operate as soon as the compressor starts, you need to tap into the compressor clutch wire and make it kick start a relay that will bridge the fan trigger circuit to ground hence kick starting the fan, you can also choose to use the same relay to directly supply 12+V to the fan with some heavy wire to make it full speed.

beware - your car will sound like a jet when the fan works at full speed - it will also shorten the fans life too.

Thanks.. I thought the low speed setting was triggered by the A/C s32 switch and the hight speed was triggered by a temp sensor on the coolant. I think bypassing it should only set it to low continuous which looks like its fine for what I need. If Im wrong about the speed I need to know. It doesnt seem like high

you are correct.