Hey Guys,

So my AC works well when the compressor decides to kick on, had it recharged last year. It only doesn't engage occasionally. I've noticed though that on long drives running AC car is fine, but in stop/go traffic the thing climbs to 110/115C. Hard to get it down even with heat blasting into the cabin.

Is my AC compressor bad? Is that causing the overheating issue? Otherwise for the most part the car runs 80C or 88C in summer.

I've also heard of folks hotwiring a switch to the aux fan in front of the rad. I would love to learn more about that if anyone has done it, what part did they use, etc.

thanks,

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1987 300td 240k #14 head

The stock cooling system is inadequate. Add a worn out viscous clutch and dirty radiator and you're bound to have problems. I had a switch in the dash for the aux fan but honestly, it doesn't move a lot of air even on high speed. 2 electric puller fans are far more effective at pulling air through the radiator. I used a BMW fan switch to turn on the fans at 92c. 71c thermostat also helps.

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CENSORED due to not family friendly words

It's running too hot. I live in Dallas and mine never went above 105C even in 100F+ weather. Probably you just have an accumulation of things on an old car - crud between the condenser and radiator, bent fins, weak viscous clutch, etc.

It is slow to come down once heated up. Once warmed up to 105C it would take several minutes of driving to come back down to 90-95.

Do you know the Aux fan comes on at low speed when the A/C is on? Check the Rec/Dryer area. There are 2 switch sensors. One is low pressure switch to indicate freon is fully charged. One is a high pressure switch which activates the Aux fan at low speed. Jump the high pressure switch and the Aux fan should comes on. It not then the resister R14 may be busted. I am not sure where is it located in the W124, probably same as the W126, underneath the brake booster area.

It is easy to jump the Aux fan at high speed. Locate the temperature sensor on top of the radiator hose in the engine block. It is a 3-prongs sensor with 2 connectors - one 1 prong, one 2 prongs. Locate the 2 prongs connectors and short the 2 pins. The Aux fan would come on. Just install a switch there to simulate the sensor is making contact internally, or temperature is reached. It should make contact if the coolant reaches 100C or 105C, depending on the sensor part #.

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Not MBZ nor A/C trained professional but a die-hard DIY and green engineer. Use the info at your own peril. Picked up 2 Infractions because of disagreements. NOW reversed.

W124 Keyless remote, PM for details. http://www.peachparts.com/shopforum/mercedes-used-parts-sale-wanted/334620-fs-w124-chasis-keyless-remote-%2450-shipped.html

1 X 2006 CDI
1 x 87 300SDL
1 x 87 300D
1 x 87 300TDT wagon
1 x 83 300D
1 x 84 190D ( 5 sp ) - All R134 converted + keyless entry.

Have you done a thorough cleaning of the cooling system? De-oil, de-calcify, new coolant?

While you're at it it wouldn't be hard to clean the outside of the radiator and condenser.

Probably at some point you'll have to deal with the fan clutch though, if its cooling good while moving and not while sitting still the fan clutch is probably at fault. Be glad its not the 2 year only electromagnetic jobbie in my 190D...

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Sadly Benz-less

go to a dealer and get a fan blade from a 98 E300D and order the new clutch from this site, and install them. then get the cooler aux fan temp switch installed on the dryer, then clean the crud from in and between the condenser, and the radiator.
then remove all the 134, and install the proper R12 refrigerant in the system.
poof.
the car will now drive and cool properly.

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

Hey Guys,

Thanks for the info. I was able to jump the Aux Fan connector and get the fan running, so that works. And I feel it does come on around 105C but never remember to check because I'm driving. I will try and install a switch and possibly an indicator light to tell me if the Aux Fan has engaged. I think I can do it without interrupting the heat sensor.

I'm sure my clutch is original, so I should probably look into that as well. Will look into 98 blade and making sure I'm running R12 as well.

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1987 300td 240k #14 head

Wanted to update with some pics on the new Aux Fan switch, working well.

Will swap out the viscous clutch and fan next, my coolant, rad and condenser are all very clean and well-maintained, so I feel the old fan/clutch may be the issue.

Attached Thumbnails

   

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1987 300td 240k #14 head

My instructions work? One comment is that it looks unsightly. Can you route the cable underneath the dash, instead of THRU the dash? Anyway, it resolves the problem, it is only cosmetic.

Good job.

__________________
Not MBZ nor A/C trained professional but a die-hard DIY and green engineer. Use the info at your own peril. Picked up 2 Infractions because of disagreements. NOW reversed.

W124 Keyless remote, PM for details. http://www.peachparts.com/shopforum/mercedes-used-parts-sale-wanted/334620-fs-w124-chasis-keyless-remote-%2450-shipped.html

1 X 2006 CDI
1 x 87 300SDL
1 x 87 300D
1 x 87 300TDT wagon
1 x 83 300D
1 x 84 190D ( 5 sp ) - All R134 converted + keyless entry.

Yes, for the switch I used Ring Tongue Terminals so I could put the original switch over them. Seems to work well. My fan never came on when A/C was on, so I never got far with that. This works well, and I'll see if I can't run it underneath. Thanks again.

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1987 300td 240k #14 head

Speaking of cleaning the space between the condenser and radiator - what is the best way to do it without dismantling the whole front of the car? I have been contemplating cleaning the radiator on my '87 TDT but haven't figured out a way to do it.

Tan
'87 300TDT

the best way is to remove the radiator, which often requires removing the fan...

__________________
John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

the original fan clutch on the 603 fails rapidly, and it's not a good idea on our #14 head equipped vehicles to scrimp on cooling. the 606 clutch is cheap, and the turbo 606 fan blade works well in the space we have on the car. TOTALLY improved the cooling characteristics of my wagons.

__________________
John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

Any chance your sound capsule is in tact and that the flaps are not opening?

__________________
http://superturbodiesel.com/images/sig.04.10.jpg
1995 E420 Schwarz
1995 E300 Weiss
#1987 300D Sturmmachine
#1991 300D Nearly Perfect
#1994 E320 Cabriolet
#1995 E320 Touring
#1985 300D Sedan
OBK #42

Quick Update, replaced the fan and clutch with new plastic fan and new clutch. Everything seems to cool as its supposed to. Still use the aux fan jump switch occasionally only as a preventative measure in high heat with AC. Thanks for all the help...

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1987 300td 240k #14 head