It won't lock up. That's what the low pressure switch does. The low pressure switch keeps the compressor from kicking on when freon is low. That keeps you from damaging the compressor
It's not hard to do but you will need to have someone do it. They need to evacuate the system and do a leak down test before you recharge it. I do all my own work. I would check the fuse and relay first tho
Check fuses first. I know of a way to see if it's a freon issue before you spend money. I just don't know where the low pressure switch is on your truck