Last weekend we took a road trip of about 700 miles. We used the A/C on the way, worked great. Spent a day at the Steel Valley Nationals in Salem, OH, didn't need the A/C so didn't use it. When we jumped in the car for the return trip and fired up the A/C, no go. When we got home, I checked the pressures and nada. Sometime between Friday evening and Sunday morning, I lost all the refrigerant for some unknown reason. It had been working fine for several weeks before that.

Today, I tried to add some back to the system and now it won't take any juice. When I open the valve to start the flow (low side), the low side pressure jumps to 120 and NO refrigerant will leave the can and head into the system. What gives?

Oh, and I'm using R134a.