My guess would be two things. First, the climate control module where you adjust the temperature is just so complicated. The second would be the fact that the air actuator is nothing more than an electric motor. Either could cause intermittent functioning.

Before you remove the actuators, you can put your hand on them and feel them working.
Since there are two identical actuators, and depending on how hard they are to remove, you could swap the good one for the suspect one. ...Before you order a new one.

Good point. I found them for about $100 at Rockauto. Better to test than to dump money.

This is a old thread, but I recently used it to diagnose and repair a passenger side hot only issue and want to add some minor updates.

1. A 9/32 socket can be used instead of a 5.5mm socket to remove the actuator

2. Grand Prix actuator will not work in the Bonneville. The have the same case and look, but the connector pinouts are different.

3. I pulled the actuator from a Park Avenue at a junk yard for $10. They asked for $17, I offered $10 and they took it (I hate negotiating)

4. I could not get the actuator to slip back onto the control door tuner. Had to open the case and move the gear so it would line up. Very easy to do.

5. The actuator will not turn if not connected to the control door turner. I hooked up the electronics and then turned the temp control the motor did not turn. Put the actuator on the control door turner, and turn the temp control, it does turn. No idea why, maybe a ground issue?

6. This thread was for a Bonneville GXP, but the SSEi (2000-2003) is the exact same procedure. I did this on a 2001 SSEi.

7. Overall very easy repair. The key is to get the replacement part cheap. AutoZOne wanted $139 plus tax for the part.

Does anyone know where the HVAC control module is located? Mine does something similar, only thing is when its hot outside the temp reads -3 or so and when its cold it reads hot. I changed the sensor in the grill with no change. I believe my acuators are fine cause when it works, it works good. When it thinks it is cold out, it turns the ac on and such, I have no manual control at all

Well, I see this thread was busy when it was cold out...but does the discussion cover the problem where HOT air blows out the drivers vents and cold air out of the passenger vents when the AC is on. At first I thought I was low on freon, but the passenger side is cold and dry. The hot air coming out of the drivers side is hot and feels humid. This just started this summer, naturally since it was hotter than hell. I'd like to tackle the problem, but I haven't felt well all summer. Any suggests will be greatly appreciated. Just turned 38k, so I wouldn't think it'* anything serious. Thanks