roadmaster heating problem

I,ve read previous threads about heat issues with roadmasters but I'm still getting no heat. Our 1992 roadmaster 5.7 has 86,000 miles on it. A/c worked all summer but now with heat needed where getting nothing. I replaced the thermostat twice (failsafe first time,then 195 degree the second) Temp gage still rises above 220--will not steady at 195 ?? Flushed out system three times--clear water with no sludge. Took off the heater core cover --core is hot with no leaks.Core is getting hot water and all the vent doors work properly,also replaced heater control valve ,still no heat. Elecronic heat/ac controls seem to be stuck on a/c-- I select 90 degrees on heat/ac controls with the economy button select as well and recieve outside air with no heat,also when I press "auto" temp selection the a/c kicks on and blows a/c cold air. What I'm trying to explain is that I believe the a/c /heat controls are not swithing back and forth from cold to hot like its stuck on air condition mode.Whatever temperature I set the controls at ,I still get A/c cold air .Any suggestions??? I,ve tried all the ideas presented in this forum,I believe? Maybe I,ve missed somthing. Water pump??
thanks

I have seemed to have fixed the fluctuating temperature gage by replacing the coolant temperature sensors (TWO)-top of block and driver side of block-there are slightly different so examine carefully when replacing.
Engine is also running better,replace plugs wires(one wire was rubbing against control arm and grounding out),distrubutor cap/rotor,and found a small vaccum leak near the carb.
Heat problem still exists. A/C will not disengage on temperature setting of any choice,otherthan economy(outside air).Is their a a/c relay ,and where is the other fuse box,checked all fuses near drivers door,but cannot find addition fuse box under hood or dash????
Any help would be appreciated.
thanks
scott