A/C secondary fan question

So- from doing a lot of forum reading I've seen that most people say that when the A/C is turned on, the secondary fan on the radiator should be running. Is this always true? Or does the secondary fan only run when the condenser needs to be cooled?
I've been dealing with no A/C for about a month, and haven't had an opportunity to really look into it because work has been pretty out of control. Last night I got home from work and it was about 90 and super humid. When I got out of my car my primary rad fan was spinning super loud like I had never heard it before and the secondary fan was off. Should this happen? OR should both fans be on before the primary one kicks into ridiculous mode?
This got me thinking- if the secondary fan has failed, would that cause my A/C to not work at all? And a follow up question, if I turned on my A/C, should the secondary fan be running whether or not something else with the A/C may not be working? I'm just trying to prepare myself for monday, my only day off, to try and figure out what's up with the fans/A/C. I appreciate any clarification I can get.
Thanks!

Well, this afternoon after work I pulled the fan carrier and disassembled the secondary fan. The brushes looked ok, but I cleaned the internals really thoroughly and made sure everything was rotating smoothly. Re-assembled everything and blam! Secondary fan is working again. Still didn't resolve my AC issue, which isn't a surprise by any means. If I'm idling and I turn on the A/C the fans still don't come on...(I'm still not sure they're really supposed to unless the condenser is warm) however, I let the car get up to 190, then sat and revved it for a while and then checked the engine bay and both fans were running nice and mellow.
One less ghost to chase for the mean time.

Could be your AC high pressure switch. They like to fail on our cars. Replaced mine last summer and recharged the system and was good to go. Symptoms included AC not functioning, pressing the AC button did not turn on the compressor. Goog luck :smile: