I have a 97 S90/960 the air cond. works fine for a while and then it starts blowing warm air. Give it a few minutes it blows cold again. My first thought was low freon. causing it to freeze up and then thaw. Hooked up a can of refrigerant. It wouldn't take any (gauge showed full) The temps here in Texas have been in the low 90s. Any thoughts? Thanks

 

If you can when it starts blowing warn pull over and check for power at the compressor.If you have power there then the copmpressor is bad.
The compressor are starting to do that when they go bad.
You can also see if the clutch acts like a magnet if it does then most likely you have power and the compressor is bad.

 

Tech,
What do you mean "acts like a magnet"?

 

The clutch itself will be disengadged and the electronic feild will still be on.
A screwdriver will stick to it when it is not spinning.By that I mean the inside part is what makes the compressor blow cold.

If the center is not spinning check for power and see if the screwdriver sticks to it.