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  #1  
Old 07-10-2006, 12:34 PM
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Aux Fan Won't Stop

My 280E (M110) rarely ran the Aux Fan. After a year at college with my daughter, it returns with the Aux Fan running as soon as the key is turned to the "on" position and doesn't stop. Searches on this Forum show lots of remedies for fans NOT working. I'm the only person who has been under the hood, as far as I know. I did some fuse work for headlights, but nothing more.

Any suggestions for diagnosing the constant "on" problem?

Thanks in advance for direction.

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'78 W123 280E, 58,000 mi!
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  #2  
Old 07-10-2006, 12:59 PM
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Check the A/C compressor wiring and switch. If it's energized the fan relay is switched on.
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  #3  
Old 07-10-2006, 02:01 PM
whunter's Avatar
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Answer:

For the cost of the two possible parts causing this issue, I would replace them both.

The A/C temperature switch, screwed into the A/C receiver dryer.

The other possible issue is:
If the Temp. Switch for Aux Fan has failed, or the wire is grounded = the fan will be on when the key is on.

PART NUMBER SEARCH RESULTS WITH PRICES
Vehicle 1978 Mercedes Benz 280E
Part: Auxiliary Fan Switch
Note: Temp. Switch for Aux Fan
212 Deg.
G5030-12319 Auxiliary Fan Switch Behr IN STOCK $31.85

http://catalog.eautopartscatalog.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=1UH0TIW001UH0TJ9UA&year=1978&make=MB&model=280-E-001&category=G&part=Auxiliary+Fan+Switch


PART NUMBER SEARCH RESULTS WITH PRICES
Vehicle 1978 Mercedes Benz 280E
Part: A/C Temp. Switch
Note:
2 spade terminals on short pigtail.
R1055-11825 A/C Temp. Switch ACM IN STOCK $31.56

http://catalog.eautopartscatalog.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=1UH0TIW001UH0TJ9UA&year=1978&make=MB&model=280-E-001&category=R&part=A%2FC+Temp.+Switch




Have a great day.
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  #4  
Old 07-10-2006, 02:20 PM
RAYMOND485
 
Join Date: May 2005
Location: CALIF
Posts: 508
Fan On

1984 300d Turbo
Your Relay Is Sticking Close Just Tap The Top Of The Relay, Replace
With New One A 5 Pin Plug In. The Compressor And Fan Are Same Type
Relay On The 300d Maybe $32.00 5 Min Done Diy
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  #5  
Old 07-10-2006, 03:06 PM
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Aux Fan controls 280E/CE

In the 78 280E/CE, your aux fan will be energized by one of two conditions, either engine temp sensor above 212F or refrigerant above 144F.

The refrigerant switch is one of the two found on your A/C receiver-drier, down in the RF corner of the engine compartment. Of the two, the other is refrigerant (low) pressure sensor, which is the final control on the compressor clutch activation chain, and actually not invoved with your aux fan. The temp switch should have just a blue (to relay) and a brown (ground) lead. If in doubt, from a cold engine start, select Temp 65 on the Climate Control, compressor switch "on" and select Auto Hi. Pull the blue lead off that blue/brown lead switch - the aux fan may stop. If the A/C clutch de-energizes, it's the other switch (I believe the pressure sw has one lead which is red and blue and another with two wires on one lead - shouldn't confuse with the blue only). If the aux fan did stop, you've found your problem, since that switch shouldn't close until the system has been running for a while and the refrigerant has got too warm [part number 001 821 73 51 - but CAUTION, you likely need to depressurize system to change it out]. If pulling the refrigerant temp switch wire did NOT turn the fan off, then the problem must lie in either the engine temp switch OR one of two relays - either the aux fan control relay (which integrates the changeover switch function) or the aux fan relay itself. (I'm looking for the numbers which you can find around the relays' wiring bundles in the "ice-cube" relay box, LF fender black covered box - I only remember that 21 is the fuel pump relay; the others are 5, 6, 8, and 12) Of course, since it's coming on as soon as you turn on the ignition switch, you can "easter-egg" the relays in the box until the fan stops - but there may in fact be two involved in the fan chain, as well as other possible involvements - but look for two to affect the fan.
[I'll also attempt to provide exact location of the temp sensor switch (likely in the head sensor box, RH side of the head, although the texts refer to a "thermostat housing temp switch", which I can't see on the actual thermostat outlet area), when I find that - pending that, you could also try pulling their leads]
Courtesy of whunter, that pic nicely sorts out the switches in the sensor box - the single-lead brass-based one (second switch back, first electrical vs vacuum) must be the engine temp 212F switch. The lead pulls straight up and off, with a little plastic catch on the plug, and should provide the other side of your logic troubleshooting. When cold, it should be "open", if you have a meter and want to ensure that it's the switch, not the relay. AND, as he also points out, if the wiring to either switch is grounding out somewhere, it will give the relay a "false positive" that causes it to energize and switch power to the fan. For that matter, you could also meter the refrigerant switch if that's "closed" when cold - to verify that blue (wrongly) goes to ground.
But your early 280E/CE Climate control wiring is NOT the same as the later 300's, according to the diagrams. CAN ANYONE PROVIDE WHICH WIRING BUNDLE NUMBER(S) IN THE 280E/CE FEED THE APPLICABLE RELAY(S), in case both switches check out okay???
The wiring diagram on the D-B CD is Diagram 4 - and located just above the Title, in the lower RH corner. When chasing diagram - make sure you note the parts/locations applicable to the 280E/CE, vs SE (diff engine switch wiring) and the 300's (different energizing wiring and an additional drier switch).
If you don't have one and have Adobe, email me and I'll try to cut and paste you a copy of the applicable .pdf.

With two switches and two relays involved, I guess it's lucky they work at all...

Happy easteregging!

Stan
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Last edited by Tristar1959; 07-10-2006 at 03:35 PM.
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  #6  
Old 07-18-2006, 04:25 PM
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Location: Po'town, NY
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Aux Fax & Relays

Trouble shooting resulted in finding relays the most likely source of the problem. Pulled Relay 8 & 9 both stop the fan when unplugged. Fan did not stop when I disconnected spade connectors at the drier unit.

I'll check for part numbers. Looking at one of the on-line catalogs, one relay cost $32, but another for the a/c compressor was $125. Hopefully, all I need is the two for $32 ea.

Thanks for all the help with this. Alex
__________________
'78 W123 280E, 58,000 mi!
'97 Mazda Miata
'94 Isuzu Trooper, 4WD
'03 MB C240 4-matic Wgn - Wife's
From the Archives:
'73 2002
'68 TR-250
'67 Austin Cooper "S"
'59 Austin Seven (Mini)
various p'up trucks
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  #7  
Old 07-18-2006, 05:05 PM
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Relays

Quote:
Originally Posted by Apodman
I'll check for part numbers. Looking at one of the on-line catalogs, one relay cost $32, but another for the a/c compressor was $125. Hopefully, all I need is the two for $32 ea.

Thanks for all the help with this. Alex
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PART NUMBER SEARCH RESULTS WITH PRICES
Vehicle 1978 Mercedes Benz 280E
Part: Relay
Note:
Originally Bosch 0 332 205 002. 5 pole terminal.
P2020-25016 Relay Hella IN STOCK
http://catalog.peachparts.com/item.wws?sku=P2020-25016

PART NUMBER SEARCH RESULTS WITH PRICES
Vehicle 1978 Mercedes Benz 280E
Part: Relay
Note: Multi Purpose
Multi function relay used for A/C : heater motor : window regulator. 5 terminal
P2037-15868 Fuel Pump Relay IN STOCK
http://catalog.peachparts.com/item.wws?sku=P2037-15868

P2020-32107 Relay Bosch IN STOCK
http://catalog.peachparts.com/item.wws?sku=P2020-32107

PART NUMBER SEARCH RESULTS WITH PRICES
Vehicle 1978 Mercedes Benz 280E
Part: Voltage Relay
Note: 5 pole terminal
P2073-12001 Voltage Relay IN STOCK
http://catalog.peachparts.com/item.wws?sku=P2073-12001
__________________
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Prototype R&D/testing:
Thermal & Aerodynamic System Engineering (TASE) Senior vehicle instrumentation technician.
Noise Vibration and Harshness (NVH).
Dynamometer.
Heat exchanger durability.
HV-A/C Climate Control.
Vehicle build.
Fleet Durability
Technical Quality Auditor.
Automotive Technical Writer

1985 300SD
1983 300D
1984 190D
2003 Volvo V70
2002 Honda Civic

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Last edited by whunter; 09-29-2010 at 02:14 PM.
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  #8  
Old 07-25-2006, 10:12 AM
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Not so fast...

Sorry, been away for a week -

Can't convict the relays until you've also checked that the head temp 212F sensor isn't going to ground when cold, which would make the relays do what they're supposed to do. Also, simply pulling them would stop the fan regardless of whether they're good or bad.

"easteregging" with other relays from the box (they're all the same relays, effectively, although you may have two manufacturers and two different types of "icecubes", the silver-cased or the blues) may isolate a faulty one. Make marks to keep your logic clear, and only swap out for one at a time...

Also, you could pull the relays and lift and meter the leads from both switches to make sure they're "open", eliminating a shorted wire as the false "switch on" input to the relays.

Let us know what you find which cures it...

Stan

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