According to shoebox's website DTC 67 is "A/C refrigerant pressure sensor circuit (pressure sensor or A/C clutch circuit problem)." The car acts funny when I turn the a/c on or off. A few times it even seemed as though the car was about to stall when i turned the a/c on or off, although it didn't stall. Also, when i turn the A/C on it doesn't blow cold air. What might cause this to happen? Any help would be appreciated.

 

It sounds like you don't have any freon left in the system. You will need to check the pressure in the system and go from there. If needed, add a can of freon and check it again.

 

How would I go about checking the pressure of the system or the amount of freon in the system?

 

You'll need a set of manifold gauges (or a friend withAC tools). Failing that, buy a chaep refill can with the gauge on it. I have R12 tools but use the cheap gauge for R134. If it reads low, add freon and see if that helps. You may find a bad hose so be careful in how fast you add the freon - don't tip the can over to add the liquid freon. I would try this first as it will cost $10 or so for the refill.
Just a side note, without taking the car to someone with a removal machine, you can't check how much freon is in the system.
If the gauge reads in the green for pressure, you will have to see if you have a bad relay or pressure switch. However, the compressor should not turn on if the pressure switch was bad or the freon was empty.