Auxillary Fans not working - 1990 300 SEL - PeachParts Mercedes-Benz Forum

matchek1 · #1 07-20-2007, 08:32 PM

My auxillary fans are now not working.

I just got my car swithed over to the frion R-134. The pressure switch to turn on the auxillary fan did not work properly so my mechanic pulled the connector from the switch to allow the fans to run all the time until I can bring it back next week so he can figure out the wiring problem.

Anyway, the fans did run all the time for about an hour. Now, even when the engine is hot, the auxillary fans don't come on at all. Fuse #1 is still intact.

Is there anyway I can get this fans turning again. The car is running really hot with the A/C on.

Arthur Dalton · #2 07-20-2007, 08:57 PM

If he pulled the connector to turn on the fan all the time, he did not unplug the pressure sw, he unplugged the temp sensor for high fan .
..and if he did not get the lowfan to come on after the recharge , there is a possibility he has not gotten a complete chage in the system to trigger the pressure sw for the low fan.
Jumper the two leads at the pressure sw at the drier [ the two pigtail wires]
See if low fan comes on.
High fan has probably now blown the load fuse .

http://catalog.worldpac.com/mercedesshop/sophio/image.jsp?title=Relay&url=http%3A//img.eautopartscatalog.com/live/P202070194OES.JPG

matchek1 · #3 07-20-2007, 09:41 PM

Thanks Arthur. You are right. The plug is for high temp. Pulling the plug used to turn on the fans, now nothing happened. Is that picture the fuse for the fans? Is that in the fuse box?

"There is a possibility he has not gotten a complete chage in the system to trigger the pressure sw for the low fan."

What did you mean by that? That he did not switch over to R-134 properly? According to the mechanic, the fan is supposed to click on at 300 psig and it does not.

Also, how do I jump that near the dryer? With a screwdriver?

matchek1 · #4 07-20-2007, 10:08 PM

By the way, you are also right - the slow fan is not coming on after they switched to R-134. Anybody have that problem?

I can see why the high-fan fuse could have blown. I went to spin both fans with the car off by hand. The right one spins fine. The left one spins when I turn it, but with some resistance. Could this have blown the fuse?

Arthur Dalton · #5 07-21-2007, 01:29 AM

You have a few questions here , so let me take them one at a time.

High fan prob has bad fuse b/c of excess draw due to binding fan motor The fuse is on top of the relay I posted for you. It is 30A..The relay is behind fuse box, in relay compartment [ 6 screws.] This high fan is activated by unplugging the blu sensor as you noted .. This is a coolant temp fan circuit and has nothing to do w/ac fan

OK..ac/low fan
This fan is activated by the pressure sw at the drier..BUT, before condemning the sw, one wants to verify the LOW FAN circuit..this is done by jumping the sw ..just slide back the white covers on the sw pigtail wires and jumper w/screwdriver [ leave the sw hooked up, just jumper the connectors]
DO NOT confuse this sw with the other spade connector sw at drier.
If the low fan comes ON , you know that the circuit is fine , except the pressure sw is not activating..BUT, it is most commonly not the sw, but rather low freon level that is the problem..if the level is slightly low, you can have cooling, but no fan b/c the high side pressures do not get to sw cut-in spec. The design is for this low fan only to come on when a High Termal Load condition exist.
He claims to have checked that and he probably has, but I would do the jumper test just for self satisfaction. I hardly ever see bad high side pressure fan sw, but tons of no fan due to low refrig levels.
The trick is to check the circuit w/jumper before any other steps are taken.

matchek1 · #6 07-21-2007, 09:06 AM

Thank you. By the way, is the reason why the high fan fuse blew due to the one fan may be going. It seems a little hard to turn..

The fuse box has for the auxillary fan, fuse #1(16AMPS). But you have a square 40 amp load fuse to replace the high fan fuse. Attached is a picture of my fuse box. Where does the 40 amp fuse go if I can get one from the dealer?

matchek1 · #7 07-21-2007, 09:16 AM

the one for the load fuse (40) amp is the white one, correct?

Arthur Dalton · #8 07-21-2007, 11:19 AM

[QUOTE=matchek1;1569150]Thank you. By the way, is the reason why the high fan fuse blew due to the one fan may be going. It seems a little hard to turn..

Go re-read my very first sentence. It states the load [Amp Draw] is suspect too high for fuse due to fan drag..

The fuse box has for the auxillary fan, fuse #1(16AMPS). But you have a square 40 amp load fuse to replace the high fan fuse. Attached is a picture of my fuse box. Where does the 40 amp fuse go if I can get one from the dealer?

I never mentioned a 40 A fuse. The fuse for load of high fan is on top of the relay..you can tell which relay by simply un-plugging the relay while the fan is ON. Do you have a bad fuse on top of any of the relays????????????

The 16A fuse is primary side of relays, not LOAD side.

matchek1 · #9 07-21-2007, 01:16 PM

The fuse for load of high fan is on top of the relay..you can tell which relay by simply un-plugging the relay while the fan is ON.

The only problem is that the fan is not turning at the moment so I don't know which relay it is. I am assuming it is either the square white one or black one from my picture. Please see my picture.

Arthur Dalton · #10 07-21-2007, 01:24 PM

[QUOTE=matchek1;1569284]The fuse for load of high fan is on top of the relay..you can tell which relay by simply un-plugging the relay while the fan is ON.

The only problem is that the fan is not turning at the moment so I don't know which relay it is

That is why I asked you to check the fuse on top ..the one w/bad fuse will be the right one. Again, pull the fuse and see if there is a burnt fuse on top of one of the relays.
They are all diffferent , so I can't tell from a picture.

matchek1 · #11 07-21-2007, 01:58 PM

no fuses are bad....

Arthur Dalton · #12 07-21-2007, 02:09 PM

OK

Run a fused jumper wire from bat + over to the aux fan resistor {behind driver headlamp..]...go to the terminal on the resistor that has the two wires.
Also, Check all connections at this resistor.
Does fans come on?

http://catalog.worldpac.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=21H0MN3YU24Z0UG8J1&year=1990&make=MB&model=300-SEL-006&category=G&part=Aux.+Fan+Resistor