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  #1  
Old 04-17-2006, 07:28 PM
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A/C not cooling very well-Aux fan problem

Just got my A/C up and semi-running (totally dead when I bought car). Anyway, air is semi-cool, vent temps when driving car get down to mid 50's with ambient temp here in OK in the 90's - when car idles AC doesn't work as well (part of this I know is normal).

Isolated at least part of the trouple - Auxiliary fan is not working at all. Here's what I have done so far - tried grounding the two leads together at the temp switch at the drier and I grounded the lead from the sensor in the thermostat housing - neither of which caused the fan to come on. I'm thinking that this should have kicked the fan on.

Can someone explain the operation of the auxiliary fan and when it should come on and go off? I'm not sure how to troubleshoot the fan?

Thanks, ryan

1978 300D

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1984 300D
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1986 560SL
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  #2  
Old 04-17-2006, 07:45 PM
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Jumping the temp switch leads (not the pressure switch) on the receiver/dryer should activate the aux fan. (The switch on the thermostat is for the blower fan.)

http://catalog.eautopartscatalog.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=1PY1E2LZD1S5145SL1&year=1978&make=MB&model=300-D-002&category=R&part=A%2FC+Temp.+Switch

I would try powering the fan directly to see if it actually works, as the next step.
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  #3  
Old 04-17-2006, 08:55 PM
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OK, just completed some trouble shooting - disconnected the fan connector (below the left headlight) and ran 12 volts directly to the fan = NO Run. Tested the lead for voltage with car running - no voltage. Grounded hte thermostat sensor connector = 12 volts, grounded the temp switch on the drier = 12 volts.

Sounds like a bad fan - if so, are they repairable? I know I can find a used one as they were very interchangeable.

ryan
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RG Newell

1984 300D
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1986 560SL
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  #4  
Old 04-17-2006, 09:11 PM
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jumper

ya, sounds like a bad fan... i use a jumper all the time..
you just unplug it from the ac drier and put a lop of wire in it..
and it should run..
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Old 04-17-2006, 09:18 PM
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A new style American automotive type fuse works well as a jumper. Plugs into the wires easily.
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  #6  
Old 04-17-2006, 09:29 PM
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One more question: Will a non-functioning auxiliary fan affect the coolling performance of the AC system that much? Or am I looking at another problem? I expected the vent temp air to be cooler than the 50's - even in the Oklahoma heat (system is still using R12).

I did check the heater hoses from the monovalve - one is hot the other one was not, which I think is the way it should be (I initially thought that the hot coolant was circulating through the heater core, countering the effects of the AC coolant). But I don't think that is happening...

ryan
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Old 04-17-2006, 10:10 PM
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Quote:
Originally Posted by rgnprof
One more question: Will a non-functioning auxiliary fan affect the coolling performance of the AC system that much?
The fan has the most effect at slow speeds and when stopped, as in "city driving." At highway speeds, it probably won't even come on. So if your a/c works well at higher speeds, your fan could be the primary problem. If not,l then the fan is not the only problem.

What type of refrigerant do you have?
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Old 04-18-2006, 12:28 AM
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R12 - I didn't want to switch, although I did convert my '72 250 to r134a and it seems to cool pretty well.

ryan
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Old 04-18-2006, 12:31 AM
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when does the aux fan come on?
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  #10  
Old 04-18-2006, 12:36 AM
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Quote:
Originally Posted by 80300dbenz
when does the aux fan come on?
When the temp switch on the receiver/drier gets hot enough to close. Typically, this will occur during stop and go driving with the a/c on. If the refrigerant level is too low, the temp will never get high enough to close the switch.
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Old 04-18-2006, 01:17 AM
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OK - here is probably a dumb question, but what exactly does the temp switch in the drier measure the temp of? My switch says 52 degrees C.
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1984 300D
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  #12  
Old 04-18-2006, 01:42 AM
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Fan

Quote:
Originally Posted by 80300dbenz
when does the aux fan come on?
When in this TX heat in traffic with AC on Motor will get hot. The sensor on drier will turn on aux. fan.
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  #13  
Old 04-18-2006, 01:52 AM
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Recirculate flap(s)

Ryan,

Is your vaccum operated "flap door" system working properly?
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Old 04-18-2006, 02:08 AM
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Since you mentioned it, where is that flap located? I'm going to be tearing into my dash soon to replace the center vent pods and I'd like to check that while I'm at it. Thanks.
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1984 300D 225K
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  #15  
Old 04-18-2006, 09:55 AM
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Quote:
Originally Posted by rgnprof
OK - here is probably a dumb question, but what exactly does the temp switch in the drier measure the temp of? My switch says 52 degrees C.
The switch closes when the a/c refrigerant reaches the specified temperature. If the refrigerant is adequately "cooled" in the condenser, then the switch will remain open (and the aux fan will not run.) If additional cooling is needed, as indicated by the refrigerant arriving at the receiver/drier above the 52 degrees, the fan is turned on to provide additional cooling air flow at the condenser.

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