I have an 04 Montero Limited heat on one side

What is your question?

My Montero Limited is only Blowing out hot heat on the driver side the rest of the vents blow out cold air. It is not duel climent control and just had all fluids in it changes by a Valvoline mechanic and even had my husband go back threw it to Burp it but there was no air in it to be found. What are some of the other causes as to why this would be doing that its got me at a lost.