R134a Desiccant and Water Binding
 

Does the desiccant used in R-134a refrigerant receiver-driers irreversibly bind water?

If not, can the water load in a drier be reduced by the application of a vacuum to the system... can a drier that has been exposed to air be salvaged by means of applying a vacuum for a sufficient duration to allow the water to boil off?

I've seen where people will pull vacuum on a system for several hours with a heat lamp shining on the filter/dryer to accelerate the process, however if the system was exposed to air for a long time, or if you're resurrecting a system that has been dead for a while, you're better off flushing the lines and replacing the filter/dryer.

Desiccant needs to be baked at 150 *F or so to dry it out. I'd say to just replace it as the heat lamp is probably not hot enough and there is no way to tell if it is actually working.