Turning on the A/C is NOT a test of the radiator fan system, it is at most a
test that tells you the radiator fan is working.  The radiator fan system
(which comes on and off in response to your coolant temp) is a completely
separate system than the A/C system (which makes the fan come on and off in
response to pressures in the refrigerant).  Therefore you need to
troubleshoot the radiator fan per the instructions on my website at
http://199.217.188.30/disc2_frm.htm.

Then you will know if it is the temp sender or a relay or fuse in the system.
I can get you a new sender for a good price if you need one.

Hope this helps,
Ken Wilford
http://www.vanagain.com
John 3:16
Phone: (856)-765-1583
Shop:   (856)-327-0027
Fax:     (856)-327-2242