Got problem with radiator fan integra 1988

I have problem with my acura integra 1988 ls automatic.
Radiator fan it's running only 20 seconds and stop while engine hot.
So i have to keep ac turn on to help engine coller.
before i replaced radiator fan switch coz the termostat still open ( upper & lower hose hot when engine hot ) but still same.
right now i totally give up.
i am short of money to bring to the shop for diagnosis / check problem. ( $100 for check only )
I need help.
thank you so much for your time.