Battery replacement - coolant fan issue

[Speedwell]

Hi new to forum but can’t see anything specific to this topic. During the covid crisis, like many others, my start stop battery went. The car is an 2014 fiesta EcoBoost 125. After jump starting I took it get a battery replaced, done by RAC technician. Everything runs fine, apart from coolant fan. The coolant fan runs only on high speed, sounding like a hair dryer coming down the street! When it got hot, or aircon was on, coolant fan would run normally at low speed, coming in and out if engine hot, or run permanently with aircon. Now the fan only kicks in and out with both engine hot (super hot hence the high speed) or aircon on, so aircon runs cold and Luke warm. I have checked relays and fuses, and nothing wrong with those. And no codes thrown up. Anyone had similar issue? I’m afraid of cooking engine! Any ideas anyone, or similar issues? Tried a reset with battery also.

[nicam49]

With my mk3 Mondeo, the cooing fans (mine has twin fans) have built into the fan tray a resistor which provides the low speed. The resistor is sited on the tray where it can get cooled - it must get very warm, ,and it's covered with a cage. It is prone to corrosion, but also the spade connectors which must carry a heavy current, overheat and break down. Now, I don't know if your model has the same fan speed arrangement, but if it does, then these are the areas I'd check first. btw, even single-fan Mondeos have the same resistor control, so the above doesn't  just apply to twin-fan models.                        I've googled 'Fiesta cooling fan resistor' and got this:

Try Googling the same, but some hits are about the heater fan, not the rad or cooling fan. Here's a screen shot of what the rad fan resistor looks like

[Speedwell]

Thanks nicam, I’ll pop down tomorrow and see what I can find!