When the heat is on the passenger side vents blows cold air. Could this be a fuse
Nope. Not a fuse. Your vents are controlled by a gate in the dash that selects either hot or cold air for either passenger. The passenger side is stuck. Any good mechanic should be able to fix this.
Search Jeep Grand Cherokee Questions
Are you a UK consumer? CarGurus now has a discussion forum in the UK.
Jeep Grand Cherokee Experts