My air condition and heating will not switch from defrost to main vents to floors vents and is only stuck on high setting and will not change. The unit is also stuck on defroster and won't switch. I don't know what the problem is? I even switched out the relay thinking that was it but it did nothing. Any help would be great!

 

When there is a vacuum leak somewhere in the system it defaults to defrost. Sometimes in the switching valve but could be anywhere. check all the lines
If you can't fix it check back with me, I have some good HVAC control units.