My heater blower works. Once the engine comes up to temperature I turn on the heater and get pretty warm air for a couple of minutes. It then starts getting cooler and cooler until there is no heat at all. I have had much work done to the system, but to no avail.
What work have you had done to “the system?” And which “system” would that be?
Be as specific as possible. We don’t want to waste your time suggesting things others have already tried. Please tell us what’s been done to try to solve this problem.
Also please tell us the mileage on this car’s odometer, and whether you drive mostly in the city or on the highway.
Is the engine reaching, and maintaining, correct operating temperature? Do you hear any unusual noises as you adjust the controls of the HVAC system? If you turn it off, and turn it back on again, without adjusting the temperature, what happens?
Have you ever had the engine coolant (anti-freeze) and/or the thermostat replaced?
My guess is the heater core is clogged. I would try flushing out the heater core.