AUX Fan - PeachParts Mercedes-Benz Forum

grafspee1217 · #1 04-28-2013, 12:00 AM

I guess this is a dumb question but what the heck. I've searched the aux fan threads on checking the temp switch in the receiver. This switch brings the fan on in low speed. The threads all refer to the fan not fans. I have two and when I jump out the switch only one fan comes on. Is the second fan the high speed fan controlled by the coolant sensor? I dont want to chase my tail if this is normal

Jeremy5848 · #2 04-28-2013, 01:28 AM

It depends on what kind of car you have. Late 124s have two fans; they should come on together. If one doesn't work, it or its wiring is bad. The 210s have two fans also but one is slaved to the other with a belt; if one doesn't work the belt may be broken, dislodged, or missing. Other models, I don't know.

BTW the switch in the receiver is a pressure switch, not a temperature switch, for turning on the fan(s) in low speed.

grafspee1217 · #3 04-28-2013, 01:56 AM

I have a 124. easy enough to check the other fan
thanks

compu_85 · #4 04-28-2013, 03:09 AM

What model and year is your car? If it has the twin fans both should come on together.

-J

grafspee1217 · #5 05-12-2013, 09:41 PM

I had a chance to check the Aux fans today. I jumped out the pressure switch and only one fan came on. There is a large connector clipped to the frame near the dryer where the harness from the fans plug in. I disconnected it and my only fan stopped. How in the world do you get them out? It's hard to tell how they are even mounted in there. Any help is greatly appreciated.

Jeremy5848 · #6 05-12-2013, 10:06 PM

You have bad wiring or a bad fan. Removal is done from the inside and requires pulling the radiator and everything else in the way. A PITA.

Jeremy

vstech · #7 05-13-2013, 06:14 AM

Quote:

Originally Posted by Jeremy5848

BTW the switch in the receiver is a pressure switch, not a temperature switch, for turning on the fan(s) in low speed.

... are you certain of this?

my understanding was the pressure switch is for the compressor and the aux fans are controlled by a temp switch. NO?

grafspee1217 · #8 05-13-2013, 07:17 AM

The fans are mounted on top of the condenser coils. How does removing the radiator help? How are the fans attached? I dont see any bolts holding them on.

compu_85 · #9 05-13-2013, 09:57 AM

The fans are bolted to the condenser coils from the sides. To get them off you have to remove the condenser. To do that the radiator has to come out.

My late W126 has a pressure, not temp switch for the aux fans.

-J

Jeremy5848 · #10 05-13-2013, 11:08 AM

Quote:

Originally Posted by vstech

... are you certain of this?

my understanding was the pressure switch is for the compressor and the aux fans are controlled by a temp switch. NO?

"All I know is what I read in the ETM" but yes, I'm sure.

The Electrical Troubleshooting Manual (ETM) for the 124 model shows on pages 121 through page 121/5 (we still don't know the specific model and year of the OP's 124) that the aux fan is triggered in low speed by S32, a "refrigerant high pressure switch," (closed 20 bar / open 15 bar).

High speed is triggered by a temperature switch, S25/5, which triggers at various high coolant temperatures depending on which version of the switch you've got. Many 124s use a switch that turns on the aux fans in high speed at about 105C and turns off the a/c compressor (through the Klima relay) at about 115C. Again, it depends on which version of the switch you've got; the color of the top is a clue to the temperature setting -- blue, gray, green, red are all possible.

High speed and low speed each have a separate relay to switch power to the fans. Low speed has a dropping resistor that lives in the left front wheel well, hear the left headlight assembly. Both fans in a 2-fan model 124 are triggered at the same time by both relays. If one fan works and the other doesn't it has to be a bad fan or bad wiring.

There is also a pressure switch for the compressor. S31/1 won't allow the compressor to run if the refrigerant pressure is below 2 bar or above 30 bar. This protects the compressor and the refrigerant circuit.

Jeremy

Zulfiqar · #11 05-13-2013, 01:07 PM

the difference between a 2 aux fan w124 is firstly ofcourse the 1 more fan.

The other difference is the high speed control, high speed is only activated by the HVAC push button system on the dash when its dedicated coolant "sensor" reads really high, about 105 C or something.

The low works from the pressure switch on the dryer like jeremy said.

The older w124 with 1 aux fan had a "coolant switch" actually trigger the high speed of the fan.

In any case both fans should work in unison as they are spliced into one connector (you can find this near the inner lower edge of the left headlamp clipped into its spring steel holder.

grafspee1217 · #12 05-13-2013, 08:33 PM

I apologize, I have a 1990 300D. I got the fans out, what a PIA. I verified it is one of the fans that is toast. The bottom trans cooler line was frozen, ended up twisting it.

grafspee1217 · #13 05-31-2013, 06:48 PM

I changed out the bad aux fan right along with a new radiator, radiator hoses, trans cooler hoses. Seems everything I touched was corroded to the point of breaking apart. The aux fans now come on low speed but I dont ever get high speed with the engine fully warmed up. There are two sensors on the tstat housing. When I pull the connector with two wires the fans go into high speed. I'm not sure on the sequence of operation for high speed. I am thinking they are temp related to the engine. I'm not sure if they kick into high speed when the engine fully warms up or if the engine starts to get too hot. It's about 88-90 degrees here and I would think that at those temps the fans would be in high speed all the time with the A/C running. Any suggestions for the newbie?