Auxiliary Fan Doesn't start

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ngruzevs
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Auxiliary Fan Doesn't start

Post by ngruzevs » Wed 18 Jan, 2017 7:18 am

Drove my 280SE for the first time this summer and noticed the auxiliary fan doesn't come on. It was a very warm day in Melbourne yesterday, hence it should have started in stop start traffic.

I can free wheel the fan, so doesn't appear to be sticky. I then replaced fuse with a brand new ceramic fuse, but doesn't make a difference. I assume it's either the auxiliary fan relay or the relay itself?

I'm sure there's a way to narrow down the fault, just need a few tips from the forum.

Also worth a mention, my aircon works fine when in driving, but when stationary it loses all it's chill
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TheMadRacoon
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Re: Auxiliary Fan Doesn't start

Post by TheMadRacoon » Wed 18 Jan, 2017 9:30 am

ngruzevs wrote: Also worth a mention, my aircon works fine when in driving, but when stationary it loses all it's chill
I think this is the result of the aux fan not coming on. The AC condensor (radiator) is not able to discharge its heat to atmosphere because of insufficient or nil airflow over it. If it can't get rid of the heat then probably the AC system cuts out on high pressure to preserve the system especially the compressor. When the car moves there is sufficient airflow to dissipate the heat, the AC gas pressure falls, the pressure switch closes and the AC system works again.
Emad,
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ngruzevs
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Re: Auxiliary Fan Doesn't start

Post by ngruzevs » Wed 18 Jan, 2017 11:17 am

Thanks for the response, makes sense. Spent some time on the car this morning and jumpered the circuit at the A/C receiver/dryer. Auxiliary fan is now on all the time. Drove the car and confirmed AC works when stationary.
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1979 W116 450SE Brilliant Red Metallic Claudia
1985 W126 280SE Thistle Green Max
1987 W126 300SE (SA Delivered) Pearl Grey Matt Oscar
1990 W126 420SE Dark Blue The Gangster
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Ivanerrol
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Re: Auxiliary Fan Doesn't start

Post by Ivanerrol » Wed 18 Jan, 2017 11:50 am

What gas do you have in the system?
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TheMadRacoon
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Re: Auxiliary Fan Doesn't start

Post by TheMadRacoon » Wed 18 Jan, 2017 3:14 pm

ngruzevs wrote:Thanks for the response, makes sense. Spent some time on the car this morning and jumpered the circuit at the A/C receiver/dryer. Auxiliary fan is now on all the time. Drove the car and confirmed AC works when stationary.
I hope someone with more knowledge than me will chip in, because I'm wondering if you bypassed the pressure switch, given where you jumpered the circuit. If so, then maybe the switch is faulty? If so, it pays to replace it so you have that high-pressure protection in the circuit.

On the other hand, I think some of these switches (iirc) also open on low gas (pressure?) so the AC won't run if you've run out of gas. So again worth having it checked.

I guess what I'm saying is it's better not to run the system with a safety switch bypassed (if that is what you have done).

Is the AC strong (cold)? When did you last have it topped up?
Emad,
TheMadRacoon
1975 350SLC Astral Silver (725) / Blue (2012, 284,900 km - present.... a real Benz, getting better and better)
1988 190E Deep Blue (900) / Cream (2006, 190,000 km - 2007, ~ 215,000 km .... FSH and still spent big $$$)
1974 280E Reed Green (860) / Bone (1993, 316,700 km - 2004, ~490,000 km and still A1)

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Re: Auxiliary Fan Doesn't start

Post by Ivanerrol » Wed 18 Jan, 2017 10:37 pm

ngruzevs wrote:Thanks for the response, makes sense. Spent some time on the car this morning and jumpered the circuit at the A/C receiver/dryer. Auxiliary fan is now on all the time. Drove the car and confirmed AC works when stationary.
Those auxiliary fans are not designed to run all the time. I installed a bypass switch across the dryer contacts with the switch in the cabin so I could control the aux fan.

When moving forward over 30 kph the fans become moot. So it's better to be able to overide the aux fan operation.
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ngruzevs
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Re: Auxiliary Fan Doesn't start

Post by ngruzevs » Thu 19 Jan, 2017 7:18 am

Max (280) was on wedding duties yesterday and as I knew it would be in stop start traffic in the high 20's, I decided to hard wire aux fan. Will be fixing Max today, I assume it will be the switch.

Air con worked fine while stationary, none of the bridesmaids or the driver (me) complained, so it looks like the lack of an auxiliary fan is causing the air con issues while stationary. I re-gassed air con two months ago, so should have plenty of gas (R134a).
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MMWA
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Re: Auxiliary Fan Doesn't start

Post by MMWA » Thu 19 Jan, 2017 7:32 am

single pin ~105c coolant temp switch on the exhaust side of the cylinder head (orange cap if original) is very prone to failure too. (even if accidentally knocked on its pin)

John green at mb spares has the febi version on the shelf for about 20ish bucks, we bought 2 of them last week. The female bullet terminal then has to be crimped slightly to give a firm connection as the pin is a "bee's dick" smaller than the original item. (NLA now I believe)

as for r/d temp switch, there are 2 versions to be aware of. Early, now NLA r/d uses small diameter threaded temp switch, black body, no pigtail, which, if i remember correctly (not 100% certain) is just metal on metal contact, the later, current r/d style uses a switch threaded directly into the refrigerant passage, large diameter red capped threaded sensor with pigtail. For this reason you should be taking it to the AC shop to replace it as the charge will need to be recovered and the system recharged.

Since you are running 134a, you should probably consider having the aux fan run with the compressor anyway - via seperate wiring and a relay which any competent auto electrician should be able to do blind folded. If your 280 has the small diameter aux fan, I would also upgrade to the large diameter v8 version like we did (malaysia ckd version car, AU version might already have the big fan)
MMWA

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ngruzevs
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Re: Auxiliary Fan Doesn't start

Post by ngruzevs » Thu 19 Jan, 2017 6:52 pm

Thanks MercMad for your detailed response.

Please excuse my ignorance within my response. I spoke to my local Mercedes mechanic today and he advised to replace the single pin switch. Is this the coolant temp switch (see pic below)?
Image

He had a red switch in stock, but also offered a grey switch that would kick the aux fan in at a lower temp. He recommended against the grey switch as he noted the aux fan may be on too much and when its not required to be on.

As you stated, he said many owners of these Gen 1 W126's make the modification to turn aux fan on when the air con is switched on and if we going to take this route he said we may as well upgrade to a larger aux fan.

Here's the current aux fan
Image

After replacing the switch I drove ~100K and outside temp was ~27C. Within the stop/start parts of the journey, air continued to be chilled and at no time did it blow warm air (like it did last week). I'm not sure if the aux fan actually came on during stop/start traffic.

Will do some more testing on Sun/Mon as temperatures are expected to be in the low to mid 30's,

Thanks again for your input.
Current Garage
1971 MK2 Jensen Interceptor Regency Red Jeremy
1979 W116 450SE Brilliant Red Metallic Claudia
1985 W126 280SE Thistle Green Max
1987 W126 300SE (SA Delivered) Pearl Grey Matt Oscar
1990 W126 420SE Dark Blue The Gangster
2013 MK7 Golf GTI White Gerhard

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Re: Auxiliary Fan Doesn't start

Post by MMWA » Wed 25 Jan, 2017 12:12 am

the red capped single pin device certainly does look like the aux fan temp switch. easy enough to tell by shorting the wire to grounded metal, cylinder head is fine and the fan will turn on if it is the one. (key in position 2)

you do currently have the small fan installed. The large fan as far as i'm aware is a drop in replacement (i didnt do this one). Your car looks nice clean and original so i'd be looking for one that is a good example if you are to do it, not tarnishing the car with something old and crappy ;) Or just leave it as is if its now working fine.
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Dean 560 SEC
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Re: Auxiliary Fan Doesn't start

Post by Dean 560 SEC » Wed 25 Jan, 2017 10:48 am

Hi Nick

I have a spare set of twin fans from a 1990 300SE if you want to go that route - in the shroud ready to go straight in.

Regards

Dean
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Re: Auxiliary Fan Doesn't start

Post by Pete49 » Wed 25 Jan, 2017 1:36 pm

I have a similar problem with m280TE (123 version) and when I hump the switch on the head it spins up no problem but when I jump the the A/C leads nothing happens even with the A/C running. The fuses are good and I cleaned them to make sure. Is there a relay hidden somewhere?
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Re: Auxiliary Fan Doesn't start

Post by Tony From West Oz » Wed 25 Jan, 2017 3:01 pm

Pete49 wrote:I have a similar problem with m280TE (123 version) and when I hump the switch on the head it spins up no problem but when I jump the the A/C leads nothing happens even with the A/C running. The fuses are good and I cleaned them to make sure. Is there a relay hidden somewhere?
Pete
Exactly what are you doing to the switch?
Please tell me that you missed out on the T in thump.
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Re: Auxiliary Fan Doesn't start

Post by Pete49 » Wed 25 Jan, 2017 9:02 pm

oops maybe it should read JUMP. oh well made someone's day lol
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ngruzevs
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Re: Auxiliary Fan Doesn't start

Post by ngruzevs » Thu 26 Jan, 2017 8:53 am

Thanks for the offer Dean, but prefer to keep the car original. So far so good after changing the red switch, air con is nice and chilled, even when stationary.

BTW, learnt that twin aux fans started fromSept 1989 (VIN A 496760 onwards) on the saloon models.
Current Garage
1971 MK2 Jensen Interceptor Regency Red Jeremy
1979 W116 450SE Brilliant Red Metallic Claudia
1985 W126 280SE Thistle Green Max
1987 W126 300SE (SA Delivered) Pearl Grey Matt Oscar
1990 W126 420SE Dark Blue The Gangster
2013 MK7 Golf GTI White Gerhard

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Re: Auxiliary Fan Doesn't start

Post by MMWA » Thu 26 Jan, 2017 5:58 pm

Dean 560 SEC wrote:Hi Nick

I have a spare set of twin fans from a 1990 300SE if you want to go that route - in the shroud ready to go straight in.

Regards

Dean
If it's anything like the twin totally shrouded fans on the w124 they actually flow much much worse than the single large unshrouded earlier fan when deactivated.
MMWA

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Re: Auxiliary Fan Doesn't start

Post by Astro-Benz777 » Sat 17 Feb, 2018 5:55 am

Fantastic and comprehensive thread with great, detailed answers.

I'm having the same issue with my '82 280SE and thought I'd do the right thing and search before opening a new thread....what do you know, an answer! :dance:
The long and short of it seems to be replacing the red topped, single wire sensor that plugs into the drivers side of the engine if I've got it right.

Just before I search &/or open another thread, does anyone here know how to remove the seat belt buckle on the front seats without destroying the plastic covering?

Thanks folks, in case it's not obvious, I'm a :sign2:
W126's truly were the last real Benz in my opinion! :occasion5:
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Re: Auxiliary Fan Doesn't start

Post by mrsecman » Thu 01 Mar, 2018 11:41 pm

Dean 560 SEC wrote:
Wed 25 Jan, 2017 10:48 am
Hi Nick

I have a spare set of twin fans from a 1990 300SE if you want to go that route - in the shroud ready to go straight in.

Regards

Dean
Dean does the twin fan displace as much air as the original? May be interested as my aux-fan is wearing.
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