I had the same problem with the right side blowing cold and the left side blowing warm. As it got warmer out, both sides started blowing warm.
That problem, along with a hissing noise from the center vents when the A/C is on, is a common symptom of insufficient refrigerant charge. The first things I would check are the evaporator temperature (#05) & the refrigerant pressure (#07) readings in the A/C diagnostic mode.
The evaporator temperature should match the heater core temperatures (#03 & #04) in the morning after the car has not been run for some time. If #3, #4 & #5 match in the morning, you can rule out a bad evaporator temperature sensor. If #5 is way off, you may have a bad evaporator temp sensor. (Although you would expect a code for the evap sensor if that were the case.) When the A/C is on, the evaporator temp should be much colder than the heater core temps.
If #3 & #4 don't match each other closely when the temps are set the same, your heater duovalve may be sticking, which could cause the driver's side air to be heated. You would see an abnormally high driver's side heater core temperature.
The refrigerant pressure (#7) must be at least 3 bar for the compressor to turn on. The pressure in a fully-charged system should be at least in the mid-teens on a hot day with the A/C running. If your pressure is in the single digits, you probably just need a recharge (and figure out the source of the leak).
If pressure is okay, try the flap test next. Flap #1 controls the cold air output of the left center vent. Flap #2 controls cold air output of the right center vent. Make sure both are working correctly.
If your flaps are okay and your pressure is okay, you could have a blockage somewhere in your system. The receiver-drier can sometimes clog. Basically anything that reduces the efficiency of the system manifests itself by blowing warm air out the driver's vent but not the passenger side. (Apparently the passenger side is cooled first.)
You probably already know how to run all these tests, but in case not, instructions are available here: http://www.continentalimports.com/ser_ic40142.html