Hydraulic clutch

Have a problem with my hydraulic clutch on 1998 S-10 with 2.2. This is the 2nd time this has happened when it is cooler out and I went to start my truck. The clutch pedal feels like there is no pressure in the line and clutch will not engage. Checked fluid level and it appears normal. Is there possibly air in the line? Would appreciate any input on this.

Need help on this one!

Yes, there is always the possibility of air in the line. However, you said it does it when it is cooler or, I assume, cold. If you had air, it would be that way all the time.
It sounds more like a possible sludge problem in the slave cylinder and bleeding would help remove this. If you do bleed, it doesn't take long to empty the resevoir so keep your eye on it.