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2003 Accord heating

My friends’ 2003 Accord blows warm air out of the right side vents, but blows cool air, at best, out of the left and center vents. We’re trying to figure out what the problem is. Any ideas?

First things first, given this description - Does this car have dual zone climate control?

Yes it does have dual zone climate control.

Yes it does have dual zone climate control.

 There is where to look.  Sorry I don't have any useful experiences with those duel controls, other than speaking with friends or riding with friends when they have gone bad.  Considering the few times I have been in a car with those systems, it must be a common problem.

Yep - time to check the climate control unit. If you can get the temperature coming out the vents to change on both sides (even if they don’t get very hot or cold), and you don’t hear any odd noises in the dash (popping, grinding, etc) odds are probably good that the control unit is having an issue. The only sources of problems I can think of for this are either a control unit issue, broken blend door(s), bad sensor, or bad blend door actuators. I’m leaning strongly to the control unit, given your description which sounds like you can get the temp to change.

I’d try disconnecting the battery for a few minutes. Some of these systems do a calibration routine periodically and if that gets messed up, they won’t work properly.

The other thing I’d check is see if the sunload sensor, ambient air sensor, or in-car temp sensors are malfunctioning. If “rebooting” the system above doesn’t work and the blend door motors are operating smoothly and quietly, pray that one of these sensors is malfunctioning. Otherwise you probably need a new control unit, and they retail for $486 for the part (labor should be cheap, at least).