My heat only blows out only front 2 right vents. Warm but not hot

When there is a problem with heat or cold not reaching one side of the vehicle, the blend doors, A/C control unit, and wiring are all suspects. The most common cause is a failed blend door/actuator. The blend doors live inside the HVAC ducts under the dash board. They function to divert the proper temperature of air to the proper location based on what the user has selected. The link below will take you to get an estimate for repairing the blend door on your vehicle in your area. https://repairpal.com/estimator/gmc/envoy