My trusted independent Mini mechanic tells me that my a/c expansion valve is 'stuck open.' What is the consequence of this? Do they ever reopen? My system sat idle for about 5 years; I'm wondering if it might reopen on its own. Short of replacement, is there anything that can be done?

 

what are the symptoms you're seeing?

 

The expansion valve meters refrigerant into the evaporator (cooling core in the dash). Think of a spray nozzle on a spray can. If the valve is stuck open it is dispensing refrigerant all the time, this can cause the evaporator to freeze solid which will affect cooling efficiency.

It may unstick with use, or it may not.

 

What might the pressures read with a frozen or frosted evap core?

 

Depends on the system. Could read very high/very low, or could read equal on both sides. Depends on the system and the mode of failure.