Ford Ranger Heater Not Working?

I have a 1993 Ford Ranger XLT 3.0 and the heater was working good until a couple of weeks ago. Then it just stopped working and I mean doesn't do anything no matter what you've got the control panel set on, nothing. I've changed the control panel and checked fluid in radiator all good. I checked all the fuses even the ones under the hood except for the square black ones. But it worked good just stopped doesn't do anything now.