Should we have to pay a $50 fee when our furnace fan stops working in January?

Each time something goes wrong in our rental house, the management company wants to charge us $50, even when it's just a faulty or broken appliance. It does state in our lease that "If the service maintenance call and/or repair is deemed routine and not due to Lessees wrongdoing and/or neglect, the Lessees will be responsible for a $50.0 repair deductible." Unfortunately we didn't read the fine print. However, we believe that renters are entitled to a working furnace and that we shouldn't be penalized when it goes out. Just because they included this language in the lease, is it legal? By the way, the single family detached house is less than 10 years old. We are 3 years into a 4 year lease. We also have an expired hardwired carbon monoxide detector. Should we have to pay for that too? We do replace smoke detector batteries at our own expense. Thanks in advance for any help you can offer.