I have a 2010 GMC Acadia and the passenger side a/c has just started blowing heat even when I only have the drivers side on. It's cool on the drivers side and hot on the passenger. Rear works

SOURCE: The air conditioner is blowing hot air on the driver's side only.

poss ac vent elec valve under dash bad

SOURCE: 2004 GMC Yukon blows hot air out of the driver

Probably the left temp actuator. The wires in the right I/P junction block could have poor tension also, but it's usually the temp actuator.

SOURCE: 2005 GMC Sierra 1500 - heater blows, but only cold air

Check coolant level. Check for heat at the heater hose going from water pump to heater core at firewall. Check to see that cable is moving coolant control valve from the closed to open position. Low mileage so it shouldn't be plugged heater core.

Testimonial: "You were absolutely correct. Low coolant level. Put in some 50/50 and we're nice and toasty now, but need to find out why coolant was so low. Thanks."

SOURCE: 2002 GMC Envoy..Air works fine out of passenger

blend door actuator needs to be replaced. dual climate controls have one for each side.

SOURCE: 2005 GMC Yukon Denali XL - Climate Control issue-

Are you aware of any codes that may stored in the body control module and do you hear a clicking or ticking noise in the rear?