following your response, I'm not sure if the system is cleared of air, how would one know if there was air in the system and remove it?

When I say the heater stopped working, I meant at hwy speeds it started blowing cold air. Now it blows hot at all times but still the system runs hotter than its regular temps. Normal temp is right at 80 and now it will jump to almost 110 at times. Ambient temps were in the low 70s that day.