fan works but just cool air coming out...logicon? heater core?

 

Had a similar problem, but it turned out that whatever the heat/cool/vent settings were from the last usage, those same settings, including fan speed, would be stuck on, and there would be no response at all to the controls. Turned out to be the ignition switch, of all things! Apparently, one of the accessory contacts in the swtich was faulty, and if I turned the switch toward off (w/the engine running) a little bit, I'd hear a slight click and the heat/cool/vent controls would work just fine. This problem would also disable my sun roof and wipers. So, if the last time the thing worked correctly, it was set to "cool", then perhaps it's the same fault. Worth a try.

 

can you change the output? such as can you switch between the defrost and vents and have the air change location? If so it is less likely the Logicon.

If you cant look at the plugs/harnesses coming from the logicon more than likely one is partially unplugged.