GMC Sonoma clutch problem?

This will sound crazy.When its hot out and I turn my AC on my clutch pedal is gone.No pressure.I have to double pump it to get pressure on the peddle to shift gears????????? Ive never heard of anything like this.I'm not loosing fluid in the master cylinder for the clutch but it seems like when its hot out I have to build up pressure to get it to shift????? There's only a slave cylinder,pressure plate,and clutch disk right?? Is there a seperate master cylinder and resevoir for the slave cylinder?? I can understand if the master cylinder was not working ,to apply pressure to the slave cylinder, to press in the pressure plate.But I thought the resevoir and the mastercyl for the slave cyl was one in the same.Does the peddle just apply the pressure??The AC thing I dont get.Is it just because its hot outside adding to the heat of the clutch system.Its all hydralic no?Aything electric?2001 sonoma 4 cyl.