I am having an issue with the aux fan on turning on when the A/C is on, the aux fan will turn on when the water temps is at 110*C thus defeating the purpose of cooling down the condenser for colder a/c. I decided to wire the aux fan to a switch so i can turn it on when the a/c is turned on. My first method was directly connecting it to the battery and powering on a switch, which works great, but the problems is it sucks up up to 1.5 amps, putting the alternator under lots of load so that did not work out well, my second option was to use a 5 pin relay, i wired everything up and jumped the relay connection to test it and its only using .30 amps that 2x less than direct connect, now my problem is trying to wire a switch to the 5 pin relay to turn on the fan, i can manually turn it on by pushing the breaker to power, but i can't use a switch, anyone know how wire a switch to a relay properly.

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Current Garage
2008 Mercedes GL320 CDI 188k mi Repair/Work in progress
1994 S350 160k mi Garage Queen & prepping for repairs
2005 E320 CDI 203k mi Healthy & Daily Driver
1994 S350 357k mi Retried as parts car
1984 300TD 214k mi Blown OM617 Poss OM603 Swap??

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1987 300SDL 200K+
1994 S320 181K mi
2008 E320 Bluetec 127k mi
1999 S420 130K mi
1980 240D 360k mi
15+ Others that has come, stay and gone

GONE, BUT NOT FORGOTTEN
1995 E320 SE 220k mi
1984 300SD 350k mi

The fan will draw the same amount of current regardless of how you tun it on.

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85 300 SD ~ 115K
82 500 SEC Euro ??K
78 450SL 164K

yeah, what's up with the 1.5 amps vs .30 amps? if it pulls 1.5 amps, the alt is barely phased. even the stock 45amp one will do fine at that load.

I use a relay on my aux fan on the 240D. It comes on when the A/C is turned on. With the A/C on Aux fan roaring the blower on high and the lights on I still have enough power on the anemic 616 to drive normal. It lugs down some but not enough to notice.

Maybe some connections are bad or your Aux fan is on the edge. The .3 amps your describing is from the fan power source or the trigger wire to the relay?
going through the relay shouldn't change your amp draw to the fan motor. At least not in a positive way over a direct wire to Batt. unless the switch you were using originally couldn't handle the motor load.

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Experience : what you receive 3 seconds after you really needed it !!



86 300SDL 387,000? Motor committed suicide
81 300SD 214,000 "new" 132,000 motor
83 300SD 212,000 parts car
83 300SD 147,000

91 F700 5.9 cummins 5spd eaton 298,000
66 AMC rambler American 2dr auto 108,000
95 Chevy 3/4 ton auto 160,000
03 Toyota 4runner 180,000 wifes

Here's a few sites on relays . The first one is good for other wiring set ups as well.

http://www.the12volt.com/relays/relays.asp

http://www.bcae1.com/relays.htm

http://www.ehow.com/how_4840454_wire-volt-relay-fan.html

Hope these help.

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Experience : what you receive 3 seconds after you really needed it !!



86 300SDL 387,000? Motor committed suicide
81 300SD 214,000 "new" 132,000 motor
83 300SD 212,000 parts car
83 300SD 147,000

91 F700 5.9 cummins 5spd eaton 298,000
66 AMC rambler American 2dr auto 108,000
95 Chevy 3/4 ton auto 160,000
03 Toyota 4runner 180,000 wifes

If you want the fan to operate concurrently with the a/c, why install a manual switch? Wire the compressor relay to the fan relay and it will all be automatic.

The fan is triggered by a *refrigerant* temp switch on the side of the Receiver/Drier.


If you short this, the aux fan will come on.

To diagnose your aux fan:

1.) Verify the fan works. Does it turn easily by hand? Disconnect the fan electrical connection under the front fender - it should read fairly low ohms. If it's open it's bad. Dead short, also bad (but probably wont be bad).

2.) Reconnect fan if it checks out (put some dielectric grease on the terminals to be kind). Jump the terminals on the receiver drier temp switch (they face towards the drive belts) together with the car off. Now, the fan should come on with the car on and the A/C on. If it doesn't, something is wrong with getting 12V to the switch.

3.) Put back to stock if steps 1 and 2 passed. Run car with A/C on for a while, then park it with the A/C on. The hotter the day, the better. Eventually the fan should come on, verifying the switch is OK. If this doesn't work, you may need a new temp switch.

For example, I have R134a in my system. It was 85 degrees where I was yesterday, and with the A/C running for maybe 5 minutes in traffic the fan came on.

This little guy is the temp switch: http://catalog.peachparts.com/ShopByVehicle.epc?q=1985-Mercedes--Benz-300d-Climate--Control&yearid=1985%40%401985&makeid=63%40%40MERCEDES+BENZ%40%40X&modelid=6193%3AMBC%7C1504%3AED%7C10000135%40%40300D&catid=242213%40%40Climate+Control&subcatid=242240@@A%2FC+Temp%2E+Switch&mode=PA

Good luck,
dd

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'85 300D, 'Lance',250k, ... winter beater (100k on franken-Frybrid 3 Valve Kit)
'82 300D, 'Tex', 228k body / 170k engine ... summer car
'83 300TD Cali Wagon 210k, wife's car

You didnt say which car your having the fan problem with,but if it is like my cars there is a big resistor behind the left headlight ,put a jumper between the terminals on the resistor and see if after the engine has run a while the fan comes on,if so the problem is in the resistor. in my case the problem was some corrosion in the connections to the resistor coil. The resistor itself is a heavy coil of resistor wire and not likely to burn out. Take it apart and clean up all the terminals then try it. Mine is still working 2 1/2yrs later.Free fix, the best kind. Don

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Red Green "This is only temporary,Unless it works!"

97 E300D 157000 miles
87 300TD ?141k? miles