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  #1  
Old 11-02-2007, 12:41 AM
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Aux fan runs all the time

1985 300DT as soon as i turn the key the aux fan starts up [i think at high speed] and runs the whole time the car is running. the engine temp was stone cold the a/c and actually all climate settings are turned off.
i searched the forums but only found threads for fans that didnt work.
is this normal?

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  #2  
Old 11-02-2007, 12:48 AM
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The most likely cause is a stuck fan relay. You might swap the fan relay with the a/c compressor relay.

The temp switch on the receiver/drier could also be the problem. You could unplug one of the leads and find out.
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  #3  
Old 11-02-2007, 01:11 AM
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I agree w/tangofox. Additionally, a third possibility is the water-temp sensor for the aux fan. Test it by simply disconnecting the 1 wire (completing a ground creates connection to the fan).
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  #4  
Old 11-02-2007, 10:46 AM
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aux fan is for a/c only, the switch on the drier should activate it. it may be bad, disconnect the switch see if it shuts off.
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  #5  
Old 11-02-2007, 11:26 AM
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great! thanks to all
can any of you describe the switches and or location of them?
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  #6  
Old 11-02-2007, 12:13 PM
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Switches

Look at your drier and you will see 2 sets of wires... follow the wires connected to the aux. fan to the drier.. you will see a set of connections.. disconnect the set near the drier coming from the aux. fan.. aux. fan cannot run with no power... the switch is attached to the drier and you can remove the switch with a wrench... just follow the wires you are going to disconnect.. The other set of wires on the drier activate the AC compressor. Jim
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  #7  
Old 11-02-2007, 02:22 PM
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Quote:
Originally Posted by vstech View Post
aux fan is for a/c only, the switch on the drier should activate it. it may be bad, disconnect the switch see if it shuts off.
On an 85 the aux fan is also for overheating protection. I have the same problem with my fan running all the time. I just disconnected it at the coolant temp switch.
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  #8  
Old 11-02-2007, 08:43 PM
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Quote:
Originally Posted by jim16671836 View Post
Look at your drier and you will see 2 sets of wires... follow the wires connected to the aux. fan to the drier..
The switch on the receiver/drier is not directly connected to the aux fan. It is connected to the aux fan relay.

Quote:
Originally Posted by jim16671836 View Post
aux. fan cannot run with no power... the switch is attached to the drier
The fan is powered through the aux fan relay, not the switch on the r/d. If the relay is stuck in the closed position, disconnecting the r/d switch will have no effect.
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  #9  
Old 11-02-2007, 09:25 PM
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ok now this is getting wierd.
on the way home tonight the temp gauge dropped down from 80 to about 60 and stayed there for the remander of the drive. this is after a few high speed accel. runs. and now the fan seems to be working ie cycling on and off. it comes on close to 80 and turns off about 60.
can anyone tell me the temps in farenheight?
i just bought this car only driven it about 50 miles or so.
po said that w. pump, expantion tank, and coolant were recently replaced. and the mileage on the car is about 52000 miles
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  #10  
Old 11-03-2007, 10:09 AM
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80C to 60C = 176F to 140F

F = (1.8 * C) + 32

or for quick and dirty, double it and add 30

Once mine warms up to about 85-90C, it stays there, whether the aux. fan is on or not. Did yours always drop to 60? Is your thermostat okay?
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  #11  
Old 11-03-2007, 02:00 PM
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i guess i may have only 2 issues; luckily not to complicated a sticky t. stat. and a possible fan relay.
i'll drive it some more to see what happens
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  #12  
Old 11-25-2007, 10:25 PM
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similar problem on a '87 300d; Aux fan on all the time after return from dealer

Dealer was trying to figure out why the compressor wasn't coming on. They didn't get done in 2 hrs on a friday afternoon... asked me to come back another day. Now, the aux fan is on ALL THE TIME from the moment I turn the key. I remember them mumbling something about the aux fan needing to be on for the compressor to run. But it never worked like that before!

Any ideas as to:

1) Fix my cpmstantly running fan
2) Get my compressor on again (stopped after the same dealer added a new starter and alternator)

... I'm not taking the car back to them. Would prefer to diagnose myself at this point.
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  #13  
Old 11-25-2007, 11:00 PM
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Quote:
Originally Posted by jle222 View Post
Any ideas as to:

1) Fix my constantly running fan
Maybe the shop jumpered the temp switch on the receiver/drier and left it that way.
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  #14  
Old 11-28-2007, 11:56 AM
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well the gauge was reading a max temp of 60, so i replaced it [the temp sender for the gauge] and all is good. temp normal at 80-85 on the gauge and fan only came on once when it was idling a very long time after a hard test drive.
thanks to all for your imput
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  #15  
Old 11-28-2007, 12:19 PM
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Quote:
Originally Posted by pizzachef View Post
80C to 60C = 176F to 140F

F = (1.8 * C) + 32

or for quick and dirty, double it and add 30
for a quick and correct, double it, subtract 10% then add 32... 99.999 % perfect conversion.

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!
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