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????????? I have never heard of anything like this.I'm not loosing liquid in the master cylinder for the clutch but it looks like when its hot out I have to build up pressure to get it to shift????? there is 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 wasn't 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 don't get.Is it just because its hot outside adding to the heat of the clutch system.Its all hydralic no?Aything electric?2001 sonoma four cyl.

I own a shop, and no your are not loosing your mind. Many fluids are receptive to temperature change, and expand or contract. This is why you check your transmission liquid level with it hot. The clutch slave cylinder must have a separate master cylinder for the liquid. When you push the pedal down, this activates a rod from your clutch pedal that works the clutch master cylinder, and in return operates the slave cylinder just like brakes do. It can not be hooked to the brake master cylinder because they're two independent systems. I could say your clutch master cylinder is low, and has gotten air in the system. The reservoir for the clutch master is on the fire wall, and typically next to the brake master & vacuum booster. Fill it up with at least a DOT three liquid, crack the valve on the clutch slave cylinder, and let it run out for some seconds. Repeat this till you have ran out about 3/4 of a glass of liquid. don't let the master get too low, or it'll put air back into the system. 3/4 of a glass should get all the air out of it. Tighten the bleeder on the slave, top off with liquid, and work the pedal some times. If the clutch is still not what it should be, then repeat the technique. If you put the wrong liquid in the clutch master, and its to get hot, then it'll make bubbles in the system, and this isn't good. This is why I say use a DOT three or four rated liquid. It has a much higher boiling point, and is suggested by the manufactures for use in all clutch master cylinders. The clutch master typically does not appear like a master cylinder, is most likely round about three four inches in diameter, and has a black cap on it.
Glad to help, Good Luck.

Certified Master Mechanic, Shop Owner, 40 yrs. experience.

there's a separate master cylinder for the clutch system also,and they have the slave cylinder,look on the out side close to where the mater cylinder is but farther down,you should see a small cylinder with a cap on it that is the master for the clutch,check it and see if its about dry,that could be the only reason other than its going out that you could have to pump the pedal to get a clutch on it,try that, if not you may have to replace it, good luck.

Yes there's a separate master cylinder for the clutch. It should be just to the outside of the brake master cyl, and lots smaller. Sounds like you ran low on liquid or it needs to be bled. You never said the mileage, it may also be showing signs of wearing out.