what is likely cause of my ac not working in my 2010 buick enclave?

Low refrigerant level is the most common problem.

It will also blink if the weather is to cold. The ambient temp sensor can go bad cause a false weather temp that will also cause the 3 blinks. When you got the 3 blinks was it the 1st time you tried the AC this season. Or has the AC not been as cold. Mine did this at the end of 2019 summer. It was corrected. This year AC was not blowing as cold as it should. Had it checked no coolent they filled it and told me to run it and come back if any issues. 30 days later AC started doing the same thing. Checked it in they found the leak at the thing that sets in front of radiator. Parts and labor in Ohio with tax 790.00 I have asthma the heat bother it. It was a must to fix. Hope this helps.