What kinda of vehicle? Do you here any hissing like a vac line off when you do this ? Does your vehicle cut out the compressor and direct air to def vents when you are under hard excelleration? Can you here the Def door opening and closing? Did you check the Def pulloff valve that moves the flapper? Just some general ideas that may or may not apply to your vehicle.
It is a 96' blazer and it had just started kicking off when the engine got a load put on it (ie big hills) but I didn't know why. I don't hear anything really when it kicks on the defroster. Thanks for the help I just need to know where to start and maybe some guesses as to the problem would help out.
Well alot of vehicles shut the compressor off when engine is under load to give you more power and instead of getting a face full of hot air it will direct the air flow up to def vents. If you have over sized tires on your rig it will seem like this is happening with less load than usual. I'm not sure technically how the system works but I think it is based on Vac pressure. So basically this is normal. There are many more "new" vehicle experts here so I'm sure you will get plenty of help.