What are the proper steps needed to troubleshoot and fix a problem of no heat in a climate controlled 1995 Buick Roadmaster that starts and runs fine but only blows cold air?

First of all if the engine starts and does get warmed up check to see that the upper hose is nice and hot. If NOT then check your thermostat as it may be open. If the engine is hot then check the two heater hoses that go to the firewall. They should be hot also. That is BOTH should be hot unless it uses a valve to close one hose. If it does you will note that. If both hoses are HOT then you KNOW you have hot coolant traveling through the heater core. Now also remember that you do this check in about 5 minutes after the engine has fully warmed up. I say this as if you wait too long..its entirely possible that your heater core is plugged up and it is merely trasfering heat through the core structure. IF both hoses are HOT your issue is with the blend door and how its controlled. If its climate controlled then the door is probably controlled by a motor or vacuum motor. You would have to check the schematic to see exactly HOW its done. As I said..if the core is flowing hot coolant then your only issue is controlling the temp. Also I might add that make sure your AC compressor is NOT working when the controller is on the heat mode. If it is its possible your AC is cooling the heat...that you want!