Hey guys! I've reviewed several of these fan inop. posts; not seeing my exact symptoms, but close.
2012 V6 convertible -
Issue: If A/C is on, the fan may/may not work - usually NOT.
Diagnostics: IF you turn ignition on, A/C OFF, turn ignition back off and then start (never turning A/C on) it works normal. Have AUTEL tool reviewing live data = 204.8 degrees, fan kicks on (cools down to about 190-195, runs there on highway consistently).
If A/C is switch ON, the ECU sends the "ON" signal to the fan (I think it was "low fan") but fan never switches on.
Last August = New water pump; when this first overheated a few months ago, overflow releasing coolant (pressure cap) = Replaced Cap and Thermostat with parts from FORD Dealer (Motorcraft);
When I garage tested (cooler temperatures) - duplicated issue, then ended up replacing the FAN Assembly (I think with Duralast)
I then moved the rear defrost relay to the high fan relay socket - then everything worked, with A/C on or off. (Also, I inspected bottom of relay box and sockets (top) - no signs of burns/overheating/melting, etc... looks really good)
But keeps failing on really hot days, stop and go driving.
Note: the built in temp gauge is shot - sometimes the needle is upside down - added 3rd party digital gauge, is pretty accurate with Autel live data.
So, recap: FAN 'on' signal being sent with A/C switched ON - fan doesn't turn on. Works perfectly normal if A/C is never turned on.
Is this a bad relay (I was about to order new relays as next step)? That's about the only variable between the "NEW Fan" and the ECU, correct?
THANK YOU for your help!