1995 Volkswagen Jetta Fan won't turn on. Termostat or sen

I have a problem with my Jettta, recently the a/c and heater radiator (the one behind the dashboard) had a leak, so I shut both hoses (connected them together) that connect to the radiator with a connector (which lets water flow between the 2 hoses).
but I ran into a problem, the fans wont start unless my A/C is on, and sometimes it still heats up (surprisingly it only heats up on stop lights, but when the car is running the temp. Goes down)