1984 300DT A/C does a swan dive......

[HuskyMan]

Yesterday driving around with the A/C operating farily well when I began to smell coolant. My passenger checked the right floor board for signs of dampness, (the carpet is out of the car so easy to see the floor board, no signs of coolant. At the same time the temp gauge begins to climb. So, I turn off the A/C and within a mile the temperature returns to normal. I left the A/C off the rest of the trip.

Last evening, I checked coolant levels (looked good), looked for blown fuses (all were OK), and pulled the newly installed monovalve to inspect. The monovalve looked good. Any ideas as to what might have caused this? I do know I need to add some R12 to the system, but things have been working fine up until this incident......