If you are talking about the heater fan, you probably didn't hook the wires up after you replaced the core, or you installed it incorrectly and the impeller is hitting something. Or you may have blown a fuse in the process.
Maybe need a fan belt
You mean the fan inside? all that wrestling around may have disconnected the plug?
It has to get hot enough to activate the thermostat switch. Normally just let it sit and at a fast idle and you should hear the fan come on, or other wise the temp switch must not be working.
I replace the heater cote for jeep grand Cherokee 2000. the fan not blowing any air
