When you lose SOME refrigerant (not ALL), the high pressure side
maintains the same pressure, but the low pressure side goes even
lower. This greater pressure differential can actually cause the
system to OVERcool the evaporator to below 32degF and cause
accumulated condensation to freeze. As more water is frozen in your
evaporator, it lowers the surface area and reduces the cooling
capacity. The pressure window in which this happens is fairly narrow,
but not non-existent. Low pressure cut-off switches are usually set
pretty low, more to prevent compressor damage than evaporator
freeze-up. This is a well-known condition. I'm surprised you don't
know about it.

On 7/17/05, Robert Cardo <rrecardo@webtv.net> wrote:
> <<<I had a similar problem that was somehow caused by the system running
> out of Freon>>.
> 
> Now here 's miracle.
> 
> The system is out of refrigerant and it's causing the evaporator coils
> to freeze up.
> 
> Having a low prssure cut off switch in your system wouldn't allow the
> compressor to kick on , but the coils froze up anyway.
> 
> I am truely amazed.
> 
> Give me the mechanic's phone number, I need for hime to wave his hand
> over my empty system too so it'll freeze up with nothing in the AC
> system.
> 
> Is his name Moses?
> 
> Maybe I can hand him a wooded staff, so he could hold it over my engine
> and stop all the oil and coolant leaks while he's whipping up this AC
> miracle.
>