[GTP Dad]

It sounds like the thermostat is sticking closed and then opening all at once. Replace it for a few bucks. Also check the fan relay, it could be going bad or the temp sensor for the fans is shot and not allowing them to come on at the correct time. You should be able to see if there is a problem with the fans themselves by turning the AC on as the fans should run all the time. If they don't come on then you may have to replace the fans themselves.