Expert: Roland Finston - 6/25/2011

Question
i have a 2001 chysler 300m 3.5L it has dual fans both work fine without ac but once i turn on the ac one fan stops and my car starts overheating ive changed the fan relay but that was not it what else could it be

Answer
Hi Rose,
That is unusual because if you are sure that both fans work without the AC, first starting up both the fans on low speed, and then as the temp rises both fans go to high; then it should also do it with the AC in play, in fact the high speed should come on at a slightly lower temp situation with the AC in play. I can't understand how that which you describe is happening unless there is an issue with one of the fan motors or one of the fan relays.
When you say 'overheating' do you mean so high as to boil over?
Are you certain that both the high speed fan positions are not coming on at all, or might it have come on and then one fan goes off? And when one is off, is the other fan doing high or low? When you say you changed the relay, did you find the relay to be located at the fan or in the power distribution box? and since there are two relays in either case, which relay did you change? I note the in '99 both the relays were in the power box while in '04 there is one at each fan position so I am not certain what is the actual layout in your '01 because I don't have the manual for that specific year model.
Another approach would be to get a fault code readout from the computer memory which you can get for free at most nationwide auto parts stores such as Autozone. Such a readout might tell us exactly what is wrong.
Roland
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