Ford Repair: bad heater, mercury grand marquis, 1989 mercury grand marquis

Question
I have a 1989 Mercury Grand Marquis LS sedan. It has 260,000 miles and has the 302 V8. The car has the HVAC system if that helps. In the winter the heater doesn't do much heating. It has done this since my parents bought it five years ago, except it is getting worse by the year. Last year the main heater that I had was the defrost, and that still didn't do much for defrosting , or heating. The "mix heat" and other heat options will work, but they don't do much. The rear defrost works perfectly. The A/C is ice cold, and still works normally. I haven't done anything to fix it: nobody has looked at it, and no parts have been purchased for it. If you do know what is wrong with it, could you tell me the best place to take it,and what the best parts are to fix it so that I can fix it right, or have someone else fix it right. I hope the best, and thank you for reading this.

Answer
first go outside and check the coolant in the radiator while it is cold make sure it is full and not dirty

if it's ok-start the engine let run to operating tempature-feel the top radiator hose make sure it is hot-if it is check the two heater hoses rear of engine area while the heater is on feel both of the hoses they both should be hot if they are both hot but very little heat inside car then you will need to take it somewhere and have it checked out could be hvac temp sensor in car or outside-it one hose is hot and the other is lukewarm then heater core is probably restricted and you may be able to flush it out check that then get back to me let me know how the hoses are-if there is a sensor in one hose be sure and check it on both sides of the sensor.