Most times when you buy a used car as is and signed an agreement stating you're buying the car as is then you won't be able to sue the person or dealership for a lemon car and then the lemon law doesn't apply in those cases.
An exception though is if you received an express written warranty along with the used car you bought then the lemon law may apply to the as is car purchase.
You should always look the vehicle over before purchasing it and even have a trusted mechanic give the vehicle an inspection before purchasing a used vehicle especially as is.