Cooling fan comes on when engine is cool and ignition SOLVED

malstc · Postby **malstc** » Tue May 18, 2010 2:37 pm

Hi all, I've been lurking for a while but it's time to tap the collective wisdom of all you enthusiasts!

I've sorted many of my problems after getting my first mx5 a few weeks ago. But I've developed a battery flattening problem with my cooling fan.

The cooling fan behaves normally when the ignition switch is on. Shorting the TFA connector and the Thermoswitch connector both fire up the fan. The fan seems to operate normally whilst driving. When the car cools the Thermoswitch goes open circuit as I expect.

However, after the car has been parked for an hour or so the fan fires up and doesn't stop. I am measuring around 11v on the coil terminal of the fan relay so I assume I'm getting stray voltage from the ECU (or somewhere?) when the engine is cool and off.

Can anyone shed some light on what might be going on?

Malcolm

bruce · Postby **bruce** » Tue May 18, 2010 4:19 pm

Could the relay be at fault? Replace it?

malstc · Postby **malstc** » Tue May 18, 2010 8:22 pm

Now Solved!

I had removed the AC a couple of weeks ago. The AC relay had fallen off it's post so I tucked it out of the way - upside down...

It had filled up with water and started to corrode finally alowing enough current back upstream into the cooling fan relay, tripping it in reverse by the looks of it. I realised I was measuring voltage across the Cooling fan relay coil in reverse to what you see when when the ignition is on

I've now removed the AC circuit tail inc the relay.

A weird one, but all is good.