This is a bottom up approach to check if the tree is an AVL tree or not. So how this code works is:
Suppose this is a tree :
cl = cr = 0
cr += 1
Your immediate problem is that you don't seem to understand local and global variables. cl and cr are local variables; with the given control flow, the only values they can ever have are 0 and 1. Remember that each instance of the routine gets a new set of local variables: you set them to 0, perhaps increment to 1, and then you return. This does not affect the values of the variables in other instances of the function.
A deeper problem is that you haven't thought this through for larger trees. Assume that you do learn to use global variables and correct these increments. Take your current tree, insert nodes 4, 9, 10, and 11 (nicely balanced). Walk through your algorithm, tracing the values of cl and cr. By the time you get to node 10, cl is disturbingly more than the tree depth -- I think this is a fatal error in your logic.
Think through this again: a recursive routine should not have global variables, except perhaps for the data store of a dynamic programming implementation (which does not apply here). The function should check for the base case and return something trivial (such as 0 or 1). Otherwise, the function should reduce the problem one simple step and recur; when the recursion returns, the function does something simple with the result and returns the new result to its parent.
Your task is relatively simple:
Find the depths of the two subtrees. If their difference > 1, return False else return True
You should already know how to check the depth of a tree. Implement this first. After that, make your implementation more intelligent: checking the depth of a subtree should also check its balance at each step. That will be your final solution.