A/C Aux. fan Temp. and Switch question - PeachParts Mercedes-Benz Forum

snookwhaler · #1 03-15-2009, 09:03 PM

I have not been able to drive my car so I have been looking at some other things that have been bugging me.

When you switch the A/C on, should the Aux. fan immediately come on or does the freon have to get to a certain temp. before the Aux. fan comes on?

I disconnected the wires at the temp. switch (by the drier) and tested the fan. It works fine with no noises. I'm assuming this means the relay is working?

I have yet to hear the fan come on and I DO NOT want to burn up my A/C compressor.

Is there a way to test the temp. switch? And can it be replaced without discharging the system?

This is an R12 system.

AJ

tangofox007 · #2 03-15-2009, 11:48 PM

Quote:

Originally Posted by snookwhaler

When you switch the A/C on, should the Aux. fan immediately come on or does the freon have to get to a certain temp. before the Aux. fan comes on?

The refrigerant must reach a specified temperature in order for the switch to close. On my '82 300D, the fan operates only in stop & go traffic on relatively hot days.

Quote:

Originally Posted by snookwhaler

I disconnected the wires at the temp. switch (by the drier) and tested the fan. It works fine with no noises. I'm assuming this means the relay is working?

The temp switch controls the relay.

Quote:

Originally Posted by snookwhaler

I have yet to hear the fan come on and I DO NOT want to burn up my A/C compressor.

If your refrigerant level is more than slightly low, it won't get hot enough to trip the switch.

Quote:

Originally Posted by snookwhaler

And can it be replaced without discharging the system?

Depends on whether you have an original style drier and switch or not. Some aftermarket switch's penetrate to the refrigerant.

This switch can be replaced with no effect on refrigerant:
http://catalog.peachparts.com/item.wws?sku=W0133-1628934

The switch, however, is not at the top of the list of probable suspects.

snookwhaler · #3 03-16-2009, 03:57 PM

Yep... That switch you listed is the one.

Can I put the head of the switch in some hot water and stick an ohm meter on it to test it? Or is there a better way.

The lines near the drier get pretty hot when the A/C is on and the car is sitting. I tested the switch in this condition and there was no reading on the meter. But I have no clue how hot the refrigerant was.

meltedpanda · #4 03-16-2009, 04:04 PM

on my 84 300SD the connections at the dryer were not complete and the fan would not come on, so dont miss the obvious like did

The fan should come on when the engine temp gets above 100 -110C no matter if the air is on or not

snookwhaler · #5 03-16-2009, 04:11 PM

Quote:

Originally Posted by meltedpanda

The fan should come on when the engine temp gets above 100 -110C no matter if the air is on or not

I thought the Aux. fan on the 123's was ONLY for the A/C?

So, the Aux. fan should come on when engine temp. rises too?

tangofox007 · #6 03-16-2009, 08:04 PM

Quote:

Originally Posted by snookwhaler

Can I put the head of the switch in some hot water and stick an ohm meter on it to test it? Or is there a better way.

According to the manual for the 1982 300D (close as I can come to '85) the switch should close at and above 144*F.

meltedpanda · #7 03-16-2009, 08:29 PM

on my 126 the fan comes on when the engine get hot, but then again it never gets hot until the AC is on- but I think it still comes on when the engine heats up without the AC, in any respect, sorry to confuse the situation

bobodaclown · #8 03-17-2009, 09:05 AM

The aux fan will com on if R-12 temp is over 73C (164F).

meltedpanda · #9 03-17-2009, 09:33 AM

Well at least I am not crazy

snookwhaler · #10 03-17-2009, 09:58 AM

Quote:

Originally Posted by meltedpanda

Well at least I am not crazy

This is why I am asking. I searched extensively before posting this thread and found numerous posts stating that on the 123, the Aux. fan is ONLY controlled by the Temp. switch on the drier and others saying that it is controlled by that switch and one of the 2 switches on the thermostat housing in conjunction with the relay. Lots of conflicting threads on this.

Maybe it does not come on until it is "hotter than 40 hells" outside?

Also, all the info. I could find on the aftermarket temp. switches says that they come on around 52 C or 125 F. That is a lot less than what others are stating. So, more confusion....

I have tried to find a good schematic for the 85 model. Does anyone know where to find one that is actually legible?

tangofox007 · #11 03-17-2009, 11:34 AM

Quote:

Originally Posted by snookwhaler

Also, all the info. I could find on the aftermarket temp. switches says that they come on around 52 C or 125 F. That is a lot less than what others are stating. So, more confusion....

Don't be confused by the fact that aftermarket parts might be different than OE parts!!!

Interestingly, my book shows different trigger temps for different vehicle models, even though the switch is the same. The figure that I provided is per the MB Electrical Troubleshooting Manual for the '82 models.

Additionally, that book shows no coolant temp switch in the aux fan circuit for either the W123 or W126 models. I can say with absolute certainty that coolant temp plays no direct role in the operation of the aux fan on the '82 W123 or W126 diesel models.

tangofox007 · #12 03-17-2009, 11:36 AM

Quote:

Originally Posted by meltedpanda

Well at least I am not crazy

Let's not jump to conclusions on the basis of hearsay!!!

Quote:

Originally Posted by bobodaclown

The aux fan will com on if R-12 temp is over 73C (164F) or if the coolant temp is over 100C (212F).
There are 2 different sensors to turn on the aux fan.

Is this based on the assumption that a W123 must be like a W124?

bobodaclown · #13 03-17-2009, 01:38 PM

I've gotten conflicting info. Under the wiring diagram it shows only the R-12 temp switch (not the coolant temp switch). But under the system description it describes both switches.

meltedpanda · #14 03-17-2009, 02:18 PM

OK then , I am crazy, I'm cool with that (lol)

leathermang · #15 03-18-2009, 10:20 PM

You are in Florida.... Wire up your AUX fan so it comes on when you have the car running.
I am sure your radiator is not 100 per of original , same for your condenser... the extra load on the alternator will not be much and will keep your engine from overheating when your engine cooling fan clutch gives up the ghost in traffic one day.....
LOL