Pin 7 discharges the capacitor after it has fully charged. So, if you made the resistor almost zero, the capacitor would discharge very quickly.
This produces an output that is mostly high but with a very short low time.
If you could make the resistance zero, the output would stay high all the time but there is a risk that the transistor that discharges the capacitor (inside the chip) could get damaged, especially if a large electrolytic capacitor was used.
i recently bought my 555 timer and i simply can't get it to pulse. I flick on the switch and i get my buzzer to work that is connected to the output but i don't hear it turn off and on. I set my configuration as astable 6.5 Hz. i checked all my connections and everything seems right. However during my first run, i connected my timer circuit parallel to 1k that was instead of two 1k connected with source along with 30 ohms the circuit (that gave off 9v 8mA). And during my first 2 runs my timer was heating up really fast. After adding another 1k to the source (as the pic) i was able to get 5V and then it didn't heat up. I even checked my simulation with multisim and despite of that i don't get any pulse (the buzzer jus keeps going and no beep).
I am thinking its either i burned my timer or i got the pinning wrong. Check both my image files to see i am doing anything wrong. Btw 9V with 30 ohms in series depicts my adaptor that gives off 9V with 300 mA