The simple answer is turn on the A/C compressor. If you have a late 67 you have auto temp control and the system should do it automatically. If you have an early 67 you would need to turn on the A/C and move the temp lever over to the warm side to avoid being cold. The A/C operation takes the humidity out of the air inside the car which is why there is a puddle of water under the car after you have been using the A/C.