I traced my inoperable aux fan to the temperature sensor on the AC dryer. This can't be changed without opening the system.

My question is; is there a downside to shorting the leads to the sensor? I verified that there is no voltage to the fan if the climate control is off.

I'd run them through a switch or relay if the current is high for control. The downside is the electrical load, overuse of the fan and a possible??? airflow restriction if they run on the highway.

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"Rudeness is a weak man's imitation of strength" - Eric Hoffer

What car?

No op of the high pressure switch will not stop the aux fan from running at high speed. The switch at the AC dryer controls the aux fan at slow speed. The switch on top of the radiator hose controls the aux fan at high speed. So the car may have other issues if the aux fan doesn't work. It could be the fan or a relay.

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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.

Thank you gentlemen, I'll hold off and check further.

I noticed I committed the cardinal sin of not saying what I was working on. it's a 1985 300SD w126.

I had issue with my aux fan not coming on my 85sd, tried a few things and couldn’t figure it out until someone here suggested take it off and take it apart and clean it. And yep that was the ticket
Been running great this year.
greazer2b

I traced the problem to the switch on the dryer. The fan runs when supplied with battery voltage. If I jumper the connections to the switch and engage the air conditioner the fan runs. I just can't change the switch without opening the AC system, something I don't want to do again until R134a goes on sale this fall.

The relays, fan, and controls all work. I was just curious if cutting the dryer switch out of the loop would have any adverse effects.

I'm a native Tennessean speaker and don't always communicate too well. ;>)

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1985 300SD Turbo Diesel

The pump fan is supposed to do the heavy lifting with this system. The aux fan isn't supposed to come on automatically with the A/C on all models. In most cases, the switch only triggers when A/C pressures exceed some high threshold. It's been awhile, I don't remember the triggering pressure. The downside of overriding the switch is that the fan will run more often than it has to, so wear on the fans and relay. If this is what you want, just do it.

This has been my stop gap solution on my 91 300D. For no money and no effort, I have AC and no overheating. I'm reluctant to get it properly repaired....but I guess I may be accelerating the demise of my 32 year old fans. I will disconnect in the fall.

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14 E250 Bluetec 4Matic "Sinclair", Palladium Silver on Black, 159k miles
06 E320 CDI "Rutherford", Black on Tan, 179k mi, Stage 1 tune, tuned TCU
91 300D "Otis", Smoke Silver on Tan, 145k mi, wastegate conversion, ALDA delete

19 Honda CR-V EX 77k mi
Fourteen other MB's owned and sold
1961 Very Tolerant Wife

I have my aux fan on a relay sensed from the compressor. living in the south, if I'm running the AC, I need the fan.

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1977 240D auto w/OM616.916 engine
2005 Matrix 5spd
2006 Prius

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