Are landlords allowed to charge tenants for normal wear and tear items?

I've been living in my townhome for 3 years now and every time something breaks or is not working properly the management company wants to charge me. For example, the charged me a part that needed to be replaced on their washing machine in my unit, they also charged me to replace the water filter in the refrigerator. Now my air conditioner has stopped working and I'm afraid they will charge me for this as well. Is this something they Can charge for? I did review my contract and it states nothing about charging me for normal wear and tear.