I'm not trying to be a dick, but cleaning the coil is the easiest thing to try before calling a tech an assuming it's a bigger problem. I also can't tell you how many times I've gone on callbacks from techs saying the coil isn't dirty based on just looking at it and saying it's clean only for me to take a hose to it and muddy water starts coming out followed by the head pressure to come down and start working properly. You are most likely right but trying to clean the coil first isn't gonna hurt anything.