Well sorry to say you surely can't make him go see a psychiatrist or any doctor for that matter, if he is not ready or willing to do so. Unless of course that person is a danger to himself/herself or others, then you can call the police and have them decide whether they need to be sent to the hospital or not. It costs quite a bit of money to have a psych eval, and the psychiatrists do have a psych eval at the first visit as far as I understand. And then the other visits aren't too cheap either, at least not at first. It's good if you have health insurance that will cover this of course.
Only a psychiatrist or psychologist can really diagnose him as whether he has Bipolar or some other illness. We can only guess here as we are not doctors. It is very hard at first when the person becomes sick, as they don't know what is happening to them or what is wrong with them, and yet they may know something is indeed wrong. They don't always know what to do or where to go. Bipolar is treatable, however, there is no real cure at this time.
Besides, there are other things that may help Bipolar such as vitamins and the correct nutrition. Sunshine is a huge help to most. Darkness is bad. Omega 3's (Fish Oil) is supposed to help some mental illnesses. Check out other preventive medicines.
Remember yes it is a chemical imbalance in the brain and it is indeed a medical condition. Many people have it, you'd be quite surprised.