As Durb has mentioned, it sounds to me like you may have an inside the air conditioner leak. There is a divider (usually stiff foam) that separates the "warm" or intake side of the air conditioner with the "cold" or output side. If that divider has slipped out of place or was not installed correctly you could have some of that cold air being forced out the exhaust of the intake instead of into the trailers air conditioning ducts.
Also, the ducts themselves, where they attach to the air conditioner, may not be sealed up correctly and you are loosing cold air to the space between the roof and the inside ceiling covering.
Maybe not but would sure be worth checking. Need to drop the inside cover and bottom plate to see.
Barney
