2002 Mercury Marquis - Auto Temp - Heater not working

I have a problem with my pristine 2002 Mercury Marquis auto temperature not working correctly.
The air conditioner works fine but I cant get any heat.
Also, I cant regulate the temp while using AC. Once the inside temp reaches the preset temp, the fan slows down but it isn't mixing with heat as needed.
Any help would be greatly appreciated.
Thanks in advance Bob Orlando, FL
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