Author Topic: Electric fan  (Read 227 times)

John H

  • Newbie
  • Posts: 8
  • W116 Enthusiast
  • Location: West Yorkshire, UK
Electric fan
« on: 06 November 2020, 12:30 PM »
Hi
1976 450SEL, euro.
My electric fan on the front of the A/C condenser is running all the time when ignition is on. Before i dive into the wiring diagram, are there any common faults which cause this?
Thanks
John

mrkozzy

  • Classic
  • **
  • Posts: 195
  • Only a Benz will do!
  • Location: Melbourne Australia
Re: Electric fan
« Reply #1 on: 07 November 2020, 07:44 AM »
John I had the exact issue the past few weeks.
Took the car to an air conditioning guy.
He diagnosed the part I've circled in the picture. A switch of some kind, I don't know the name.
Changed it over for another from a donor car and all is good again.

Try that option 1st maybe.

Note.

I have the M110 6 cylinder, could be a different issue for an 8 possibly.






MrKozzy

ptashek

  • W116 Addict
  • ****
  • Posts: 2,016
  • W116 owner
  • Location: Ireland
    • History of ZV9485
Re: Electric fan
« Reply #2 on: 07 November 2020, 11:50 AM »
John I had the exact issue the past few weeks.
Took the car to an air conditioning guy.
He diagnosed the part I've circled in the picture. A switch of some kind, I don't know the name.
Changed it over for another from a donor car and all is good again.

Try that option 1st maybe.

Note.

I have the M110 6 cylinder, could be a different issue for an 8 possibly.

That would be the pressure switch, which turns on the AC fan if the pressure in the system increases.
1993 "Pearl Blue" W124 280TE
1988 "Arctic White" W124 200T
1979 "Icon Gold" W116 450SE (history, resto)

John H

  • Newbie
  • Posts: 8
  • W116 Enthusiast
  • Location: West Yorkshire, UK
Re: Electric fan
« Reply #3 on: 07 November 2020, 12:33 PM »
John I had the exact issue the past few weeks.
Took the car to an air conditioning guy.
He diagnosed the part I've circled in the picture. A switch of some kind, I don't know the name.
Changed it over for another from a donor car and all is good again.

Try that option 1st maybe.

Note.

I have the M110 6 cylinder, could be a different issue for an 8 possibly.

That would be the pressure switch, which turns on the AC fan if the pressure in the system increases.


Thanks guys. I'll try that

John

Nabstud

  • Enthusiast
  • *
  • Posts: 49
  • W116 Enthusiast
  • Location: Perth, Australia
Re: Electric fan
« Reply #4 on: 07 November 2020, 09:34 PM »
The M110 6cyl also has a 100°C fan switch in the cylinder head near the temperature gauge sensor, as the name suggests when engine temps get over 100°C it turns the fan on. I assume the V8 has a similar sensor, you can unplug it to see if the fan stops.
1975 280S - Australian delivered

revilla

  • Classic
  • **
  • Posts: 351
  • W116 Enthusiast
  • Location: Aix-en-Provence, France
Re: Electric fan
« Reply #5 on: 07 November 2020, 11:02 PM »
By own experience I bet the problem is rather the 100 switch. Being a new acquisition maybe you have recently washed your engine. And washed the entire car too. This switch is connected to a relay covered behind the panel in your A Pillar.  In my case water drips got into that area causing your same problem. But I would remove, check and dry up both switches in question. Those 3 usual suspects is a good way to start your Sunday.
Good luck
Robert
W116 1977 280SEL & 1979 280SE

John H

  • Newbie
  • Posts: 8
  • W116 Enthusiast
  • Location: West Yorkshire, UK
Re: Electric fan
« Reply #6 on: 08 November 2020, 02:14 AM »
By own experience I bet the problem is rather the 100 switch. Being a new acquisition maybe you have recently washed your engine. And washed the entire car too. This switch is connected to a relay covered behind the panel in your A Pillar.  In my case water drips got into that area causing your same problem. But I would remove, check and dry up both switches in question. Those 3 usual suspects is a good way to start your Sunday.
Good luck

Very useful, thanks Robert and Nabstud

The engine bay hasn't been washed, but I will check those points anyway.

Which side A-pillar should I look for that relay?

Cheers, John

revilla

  • Classic
  • **
  • Posts: 351
  • W116 Enthusiast
  • Location: Aix-en-Provence, France
Re: Electric fan
« Reply #7 on: 08 November 2020, 08:56 AM »
Hi John.

Mine is a LHD and they are located on the driver’s side. Anyway, they are easily identifiable once the little panel is removed. You’ll see a vertical rack/bracket holding 3-4 aluminum cube type relays, it’s one of them.  Remove one at a time until your fan stops. Then you can swap with another one from the same rack to test. They are all interchangeable with same pins configuration.

Cheers

Robert
Robert
W116 1977 280SEL & 1979 280SE