My neighbor has a intertherm air handler that is heating, but will not turn the fan on in auto on the t-stat.?

The air handler works fine when in cooling, the indoor fan motor comes on in the auto setting, but for some reason in heating, the indoor fan motor will not come on in auto in heating mode. He has to manually turn on the fan to get any air. I came to the conclusion that it must be the Indoor fan motor relay and wanted to see if there were techs out there that may come to the same conclusion. I am checking my troubleshooting by asking on here. I used to do AC work, been out of it for five years.