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94 Cutlass Radiator Fan issues


Leadfoot
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It's been a while since I've dug into something like this and I'm scratching my head.  I feel like I'm missing something simple (2 kids and not much sleep could be to blame).

A couple of weeks ago I was letting the car run sitting in the driveway and it started getting hot.  I popped the hood and noticed neither fan was running which was odd.  I turned the AC on to get Fan 1 (driver side) to kick on and it wouldn't so I just shut the car off and let it cool down.  The next day I fired it up and let it run with the AC on.  I turned the AC on when the engine was cold and fan 1 ran.  Once the engine warmed up Fan 1 turned off and both fans stayed off.  I shut it off after a minute to make sure it didn't get hot.  Today I manually tested fan 2 and it ran fine.  Fan 1 would run when I turned the AC, but I didn't let the car get warm.  I have tried swapping relays around and the fans operate the same regardless of which relay is in place for which fan.  I manually commanded the fans individually with my Tech 2 and they both ran.  The tech 2 and the dash both seem to be reading engine temp reasonably accurately.  I just can't figure out why they won't turn on.  What am I missing?

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Start with the service manual wiring diagram.

Worst case, you have a failed ECM.  Probably something else, though.  Aren't there three relays to control the various fan speeds?  And, of course, the actual temperature sensor that controls the relay(s)

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How hot is "hot?"

On 5/19/2021 at 1:25 AM, ron350 said:

Doesn’t your car use 2 temp sending units, one for the gauge and one for the ECM?

Sender for the gauge, sensor for the ECM. His Tech 2 is pulling data from the sensor, so if the gauge is close to that reading, everything should be accurate.

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On 5/19/2021 at 12:20 AM, Schurkey said:

Start with the service manual wiring diagram.

Worst case, you have a failed ECM.  Probably something else, though.  Aren't there three relays to control the various fan speeds?  And, of course, the actual temperature sensor that controls the relay(s)

Good point.  There are only 2 under the hood and I haven't looked for the 3rd.  That's definitely a possibility.  

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On 5/20/2021 at 8:26 AM, Leadfoot said:

Good point.  There are only 2 under the hood and I haven't looked for the 3rd.  That's definitely a possibility.  

There's only 2 relays in '94. The three relay setup didn't start until later. How hot is the car actually getting that it's causing a concern? Stock fan on temps under normal conditions can be relatively high(in the 220 range).

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I need to go look at the gauge, but the first time It got up to 240ish.  The subsequent times it was that it continued heating up, but shut FAN 1 off even though the AC was still on so I'm guessing something that controls it interrupted the signal.  That time I am not certain how hot it got, but I believe it was 220 or so.  I will repeat now that I'm back in town and see what I come up with.

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