90 420SEL, AUX FANS Always On - PeachParts Mercedes-Benz Forum

qzthree · #1 10-19-2007, 09:52 AM

My father gave me his 1990 420SEL, he had his ENG out of his older 420SEL put in to this car I speak of now. THe Problems I am have ing are THe AUX FANS will not shut off. They come as soon as the key is turned and dont shut off until the car is shut off. Also thmy father said that the A/C blows the fuse as soon as the A/C is turned on. I checked the ICV, and the temperture sensor con, tro make sure they where not crossed. They where not crossed. The one prong temperture sensor has the wire broke off. I wrapped the wire around the the prong to see if the temperature gauge would work but it did not move. I dont know if the guy he had 2 put the ENG in did it right, but i could really use some help PLease.

david s poole · #2 10-19-2007, 10:02 AM

the 90 model 420sel had a 2 prong blue temp sensor and it was wired [thru relays]so that if the sensor went bad OR the plug was off the fans would run all the time on high speed.seems that on your car this sensor was left out of the swap.

qzthree · #3 10-19-2007, 11:52 AM

Thank you so much because there is a green 3 prong, they have a 2 prong wire con on the side with th 2 prong. then a one prong wire on the other side. then there is another wire con on a nother 1 prong, I think that one would have been for water temp gauge sensor. So what should I do?

david s poole · #4 10-19-2007, 12:08 PM

the green switch was replaced by two switches one of which is a two prong [or pin].until you rectify the wiring,remove fuse box cover and in the back you will see a bunch of silver square relays.turn on ignition so fans run and remove relays one at a time to identify aux fan relay and then leave it out.now it's management by design not crisis.

qzthree · #5 10-19-2007, 01:13 PM

well thanks a lot, I will remove the relay. I also check the green 2 prong it is open. My dad just told me the ENg came out of his 87, but he use the harness from the 90 420. I will buy another sensor. My last question is what type of wires and plugs you guys use?

Arthur Dalton · #6 10-19-2007, 02:02 PM

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Just the opposite.
Open circuit on thermistor fan circuits [ which is this chassis] defaults to full fan. You must replace the temp sw with a thermistor sensor in order for the stock fan circuit to operate correctly. Standard temp sw will not work with this sysem as the fan circuit is triggered by thermistor sensor resistance values, not a sensor switch contact set.
See Pooles first post on this Default disign feature.

qzthree · #7 10-20-2007, 07:04 AM

Thanks Alot, will do. Have a great weekend

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