My 93 Loyale doesn't put out good heat, it blows lukewarm air at best. It has good flow through the heater core as both hoses get very hot. Does anyone have an expanded view of the heater box or have any info on how the heater door works and where it's at? This is a 5sp with AC 4x4 wagon Then you turn the heat off with the switch it blows COLD turn the heat on it blows warmish. I suspect the heat door is not opening properly, any way to check that?

The temperature lever / slider mechanically moves a blend door that directs the air through the heater core or around it.

another possibility is to clean out the heater core.  pull both hoses and run water through it. 

You can pull the hoses off the firewall and use an air compressor to pulse air blasts through it. This helps unclog the gunk