I have changed the draft motor I'm not getting any suction to pull in the pressure switch could it be the heat exchanger. If I suck in the pressure switch it lights up.

It could be the heat exchanger and they have a 20-year warranty most of the time. It would be rare. It also could be in the draft switch being out of calibration or the motor turning in the wrong direction. The fan rotates in the direction the blades point. Did you get an exact replacement or a generic? The wrong rotation is highest on probability. DrTom4444