Well the main reason why your car blows out cold then hot is because the air conditioner may not be working properly. You should go to the car shop and get it fixed.
The Air Conditioner is on
Check to see if your condenser fan is running when a/c compressor kick on.
An air conditioner evaporator is the part of the a/c system that the heat in your car transfers to causing cool air to blow from your vents. The blower is in front of it and it sucks air from the inside of your car and across the evaporator then blows out your vents.
Could be a bad heater core...also, could be low coolant level. With my car, it was Heater matrix clogged with radiator sealant. The workshop cleaned it and it's start working fine!
I would get it checked out by a profesional because that one is a hard one to deal with if it doesnt get done right
May need to be recharged.
it could be the heater core and ac housing unit that allows hot air to be mixed with the cold air or it could just cancel out the cold due to the motion of the car
You are low on coolant to the heater core.
Try your thermostat
Actually, the AC is always blowing cold air. Its just that sometimes your nerves can't feel it because your body is used to it.
It probably needs some coolant. This is the chemical that is put in the car in order to keep the air conditioner cool. If your air conditioner is not getting cold either the coolant has run out or leaked out.
Coming out of the vents around 43 degrees