my heat wont work on my 93 sc300 lexus, it blows only very cold air. car warms up just fine. any thoughts?

I assume you mean the car does not show any signs of running cold.

My guess is a vacuum leak. Many cars use the engine’s vacuum to control various things in the car and the “blend doors” is one of them The blend doors direct hot and cold air. They usually default to cold if there is a failure. Look for a loose, missing or cracked vacuum line.