Heater/AC problem

2002 Mercury Sable. Heater was puting out luke warm air. I found a leak in the fill tank and replaced it, also flushed the system and replaced the thermostate. Still no heat, determined that the A/C is coming on when the heater is turned on. How do I resolve this problem?

Bill

With most if not all cars today the A.C. comes on to help defrost the car / windshield faster on some of the settings. Does the A.C. come on when you put the heater selector on just your feet? Is the blend door opening and closing? Did you have the cooling system pressure tested after you made your repairs? When the car is at running temp feel both hoses that go into the heater core. They should both feel hot. Meaning hot coolant is going through the heater core. Good luck.

I hate to be the bearer of bad news. I have the same problem with my 98 sable. Heater core is clogged up tight. I’m guessing you have the 3.O Vulcan engine, or in other words, the weaker of the two engine options. These cars are notorious for rusty, thick, radiator fluid problems. This is because the water jackets rust out on these cars unless they are flushed religiously. For the sable the heater core replacement will run you $600 bucks. Because I'm a poor college student, every 6 months I disconnect the heater core hoses and run compressed air through it then flush the system. This may give you some heat, but is not a sure fix. With my car, my heat works fine when I'm on the gas pedal. When I come to a red light, I loose the heat. As my heat progressively gets worse, I know its time to flush again. I first looked into the problem when I bought my car a year and half ago and all I had was cold AC like you describe.