My blower won't come on. Even if I push the trematsate way up. What is causing this. But if I push the summer button on furnace then blower comes on

The heat sequencer that controls the blower is defective.

Can you make the blower cycle on and off when you move the temperature setting on your thermostat up and down with the system in the summer setting? If not you may have a blower relay stuck in high speed and not letting the low speed work for heating.