[Hmanor3]

Assuming the cooling system is working properly, and you have hot coolant into and out of the heater core, that would indicate the problem is inside the dash. The ’98 Olds LSS is equipped with a dual zone Automatic climate control unit. The main component in this system is the programmer unit. This unit, located behind the glove box, controls the temperature, and air discharge locations. There may be problem with this unit causing your issue. But before we assume this is the problem we should check the air valve temperature actuators. There are two of them, one for the driver’s side, and one for the passenger side. One is located on top of the programmer, and one inside the programmer case on the bottom. There will be a small threaded rod attached to each of them. To check them, warm up the car and turn the temperature control down to 60, wait 10 seconds, and turn it up to 90, and look to see if the actuators are moving. One will move with the passenger control, one with the dash control, unless the passenger side is turned off, then both should move together. I would start there. They are known to stick.