Auxiliary Fan Always Running???

[wscheffer]

Hello everyone,

Since the weather started to get nice I decided to start work on getting my A/C to work in my W126 1987 420SEL. I started to examine the system and noticed that there was no fuse for the auxiliary fan.
This is number 1 in my fuse box.

So I put in a new fuse and started the car. The auxiliary fan came on running at full speed and does this as long as the care is running or the key is in the number 2 position.

I know this is not normal, does anyone have any idea as to where the fault lies or where to start to diagnose this problem

 

[television]

Hello everyone,

Since the weather started to get nice I decided to start work on getting my A/C to work in my W126 1987 420SEL. I started to examine the system and noticed that there was no fuse for the auxiliary fan.
This is number 1 in my fuse box.

So I put in a new fuse and started the car. The auxiliary fan came on running at full speed and does this as long as the care is running or the key is in the number 2 position.

I know this is not normal, does anyone have any idea as to where the fault lies or where to start to diagnose this problem

Pull the lead off the temp sender, and see if it stops

 

[wscheffer]

I pulled a wire off the auxiliary fan temp. switch and the auxiliary fan still runs.

I also tried pulling off the pressure switch leads with the same result.

I disconnected the coolant temp sender switch located at the goose neck for the upper radiator hose and the fan still runs.

 

[hmang]

is the fan powered via a relay ?

 

[Hibbo]

Hey yo word up etc.

I noticed that with the instrument cluster disconnected the aux fan runs all the time on my w124.

The temp circuit is 12v-gauge-sender-earth, and I'd imagine the aux fan switching is tapped in to monitor the voltage between the gauge and sender, lower voltage = higher temp. So if the aux fan circuit receives no voltage then it'll run.

This is all my guessing, so don't hold me to anything!

 

[television]

http://www.detali.ru/cat/oem_mb2.as...&L=765.706&CT=F&cat=568&SID=54&SGR=045&SGN=03

Item 134 is the relay, this could be controlled through the cluster as Hibbo says

 

[wscheffer]

is the fan powered via a relay ?

I belive it is by looking at the schamatic their are two relays that come into play (K9 auxiliary fan relay and K10 auxiliary fan preresistor relay) which have a two leads connecting them together.

By comming off the auxiliary fan:

Thier are two leads earth and the other appears to intersect between a K9 auxiliary fan relay lead going to the R15 auxiliary fan preresistor group.

Then exits the R15 auxiliary fan preresistor group and conncts to K10 auxiliary fan preresistor relay compleating the loop.

The K10 auxiliary fan preresistor relay is controled by S32 the auxiliary fan pressure switch.

But by going off of what Hibbo is saying if I am perceving this right and I am sure someone will correct me if I am wrong. That I can not narrow it down by pulling off wires since low voltage or no voltage is what will cause the auxiliary fan to run?

 

[television]

Dont forget that relays are in to types, normally open and normally closed, cars often use the normally open as this reduces the amount of earth return wires, also the current drawn is very low

 

[wscheffer]

Dont forget that relays are in to types, normally open and normally closed, cars often use the normally open as this reduces the amount of earth return wires, also the current drawn is very low

I understand the principal of the relays state has to be normally open or closed, but how do you tell which state is the norm for a particular relay. I have WIS installed on my PC that I obtained from a gentleman in London.

I use the term gentleman rather loosely, he was rather ignorant as I had further communications with him, but you get that everywhere

Any ways, WIS is nice to have on the PC and it has helped me to help others immensely, but the schematics that WIS is printing off are rather small visually and hard to read. So if the schematic has a marking on them in reference to the state of the relays I wouldn't be able to tell. :mrgreen:

So, I guess my next question would be is their a physical marking on the relay that indicates it's state?

 

[television]

Relays in diagrams are shown in the not activated state, so looking inside the square outline on the drawing inside you have the contacts shown. the line used for the contact switch points towards the one being used. so on a single contact relay if the diagonal line points towards an dot with no connection thats normally open, when it points to a dot with a wire going to it that is normally closed

 

[Hibbo]

Pull the relay and put an ohmmeter or continuity tester across its contact terminals (86 & 87?), this will tell you if it's NO or NC.
If it's NC then a blown relay could cause your fault. It sounds silly to use a NC relay in this circuit, but I suppose it's a good failsafe.

 

[eric242340]

Relays in diagrams are shown in the not activated state, so looking inside the square outline on the drawing inside you have the contacts shown. the line used for the contact switch points towards the one being used. so on a single contact relay if the diagonal line points towards an dot with no connection thats normally open, when it points to a dot with a wire going to it that is normally closed

Malcolm, this is the most confusing you have posted yet. Or have i missed something in this post?

 

[television]

Malcolm, this is the most confusing you have posted yet. Or have i missed something in this post?

How would you descibe the normally open or normally closed contacts on a relay with drawing out the pic scanning and posting, be my guest, the diaganal line points towards the normal state

 

[eric242340]

How would you descibe the normally open or normally closed contacts on a relay with drawing out the pic scanning and posting, be my guest, the diaganal line points towards the normal state

Im not critisising you but merely asking you to explain this better ie terminal Numbers and how to check for members who may not understand especially with relays and they all have common numbering be it Benz or toyota

 

[television]

Im not critisising you but merely asking you to explain this better ie terminal Numbers and how to check for members who may not understand especially with relays and they all have common numbering be it Benz or toyota

The time to search for that is unreasonable, it would take far too long. A simple meter tells you all you need to know or use the diagram on the relay if shown, and my answer was to the question, how its shown on the wiring diagram

 

[wscheffer]

I do understand Malcolm about the diagonal line being the primary state of the relay and if it's to a point with a wire it's closed etc...

But as I said my version of WIS is printing small diagrams too small to see the workings of the relays.

I guess I will have to get out the meters and have at it as Hibbo suggested.

Thanks Again everyone for your input. It is well respected and deeply appreciated. I will re post the results later.

 

[television]

I do understand Malcolm about the diagonal line being the primary state of the relay and if it's to a point with a wire it's closed etc...

But as I said my version of WIS is printing small diagrams too small to see the workings of the relays.

I guess I will have to get out the meters and have at it as Hibbo suggested.

Thanks Again everyone for your input. It is well respected and deeply appreciated. I will re post the results later.

Sorry to be patronising, its hard to know what others know, re WIS it is a pig when it comes to the wiring. If only the writers of the program new what a block diagram was, that would make it simpler, just to see the components in any circuit

 

[eric242340]

Sorry to be patronising, its hard to know what others know, re WIS it is a pig when it comes to the wiring. If only the writers of the program new what a block diagram was, that would make it simpler, just to see the components in any circuit

Hi Malcolm, WIS was designed to work with Star D and it works well. But if you want to find something individual it can take all day. The wiring diagrams are all there for all to see, but not as block diagrams. However, once you find the diagram then click on the red numbers and it will identify the specific part of the wiring diagram. And also there is an addition to WIS, which is a parts locator. So when star d finds a fault. you can find that parts location. Parts locator is avaible in many countries for small money And further to this the New system now is called Star net.

 

[television]

Hi Malcolm, WIS was designed to work with Star D and it works well. But if you want to find something individual it can take all day. The wiring diagrams are all there for all to see, but not as block diagrams. However, once you find the diagram then click on the red numbers and it will identify the specific part of the wiring diagram. And also there is an addition to WIS, which is a parts locator. So when star d finds a fault. you can find that parts location. Parts locator is avaible in many countries for small money And further to this the New system now is called Star net.

I understand all of that,and do not have any problem to find components, I also have the EPC but it is of no use when you want to see a closed loop of any complete circuit, electronic diagrams cannot compete in any way compared to paper, but had you worked in the electronics trade you would know that.

A simple block of a start up circuit is in the link

 

[television]

Hi Malcolm, WIS was designed to work with Star D and it works well. But if you want to find something individual it can take all day. The wiring diagrams are all there for all to see, but not as block diagrams. However, once you find the diagram then click on the red numbers and it will identify the specific part of the wiring diagram. And also there is an addition to WIS, which is a parts locator. So when star d finds a fault. you can find that parts location. Parts locator is avaible in many countries for small money And further to this the New system now is called Star net.

Just coming back to this, if you had and were using all these things how come you have never posted yet where any component is situated on any car.

I also remind you that I have been using these programs a lot longer than you, I do not have a problem with these things, the problem is with electronic media circuits in genral