2014 Ford Explorer Heater & A/C issue

My heater & A/C stopped working. Unless I drive on the highway, Heater &
A/C work. During driving in the cities, they don't work. But, Rear seat heater
& A/C working just faint air blow into. I asked for a local auto shop. All of
them say I have to pay to get info on what's a problem. I think it's lame to
have to pay. I'll pay to fix the problem. At least tell me what the problem. But
nope they want 200 dollars to just check-up SMH

Could any of you might be suspected of what would have to cause it.