Fuse F19 supplies power for the high-speed circuit on the radiator cooling fans as well as power for fuse C4 which provides power for the A/C compressor clutch. It would be my guess that the source of the problem is somewhere in the radiator cooling fan circuit. During normal operation when the engine temperature requires it, the ECU will energize CONT. RLY 3 to start cooling fan #1 (which is powered by fuse F14). When the A/C is turned on, CONT. RLY 1 & 2 energize so both radiator cooling fans will run at full-speed, powered by fuse F19.
The difference in the cooling fan run cycles (A/C on vs A/C off) is that cooling fan #2 runs with the A/C on, but not when the A/C is off, the run cycle of the fans is also higher. Chances are that the #2 fan motor is causing you the problems, but due to the increased fan run-time cycle when the A/C is on there is a small chance it could still be the #1 fan motor. It could also be a connection issue so don't forget to keep your eyes open for that.
I hope this helps.
2005 Ardent Red Elise, Gut Sport wing & splitter, custom diffuser, Sector111: DSBrace, gPan3, subStuffy2, Larini Sport muffler, decat pipe, Schroth Racing 5 pts, wheel studs, Team Dynamics 1.2 with Hoosier A6s, Koldflash 200 ECU flash, BOE rear clam hinge, BC Racing single adjustables, Hawk pads, SS Brake Lines, HID lights, custom tail and high mount brake light...and much more...