Heating issues

I have a 1991 k1500 and have no control over the heat in the cab, even though the control shows cold. As soon as I drive down the road heat pours into the cab. Where should I start?

I have a 1991 k1500 and have no control over the heat in the cab, even though the control shows cold. As soon as I drive down the road heat pours into the cab. Where should I start?
The damper may be stuck. It's near the heater core under the dash. Mine's had issues for years.

Thanks, I'll check it out.

It could also be the actuator that moves the damper. I just had to replace mine on my 90 K1500. The motor inside the actuator was not strong enough to move the damper.

I had replaced the tape deck with a cd player. I had to remove the cd player and the glove box to replace the actuator.

//2000CAYukon