93 explorer 5 spd

I have a 5 speed manual in my explorer and when the air conditioning is on and the truck has been idling for about 10 min, the clutch has no pressure and won't operate the clutch. You have to pump it up to shift and get going and then keep pumping it up for each consecutive shift after. It is a real pain in the city as it seems to take a long time to get so that you don't have to pump it up and it has its own pressure. Does anyone have any clues.

Sounds like a slave cylinder and/or a clutch master cylinder.To get to the slave the trans has to come out so you may as well put in a new clutch set.Check the fliud in the clutch master cylinder it might be low. Fill it if it's low that might buy you some time.