2007 Lucerne that is blowing warm on driver'* side but cold on passenger side.... I used a Bi-Directional Scanner to manipulate ALL the mode doors and they all work just fine......what else could I be looking at?

Dual front zone or single front zone?

Dash vents or floor vents or both?

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​​​​​​​Have you visually verified that the blend doors are working properly and sealing properly at both ends of their range of travel?

If all of the above is covered:

- Is the cabin air filter clean and new?
- Could be the evaporator gone bad.
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Evaporator only deals with the AC....the heater core is what supplies heat.

Is it dual control? If so you need to look at the temp sensors on the scan tool and see what you have. They usually code for open and shorts but may not for one that'* just whacked out.

It is dual control and everything works when I activate it with my scanner, and in looking at the other parameters I don't see any problems.....I'm stumped.

​​​​​​​Yes, but what I don't know is what air conditioning mode has been selected.

If heat is selected and it is blowing warm on the driver'* side and cold on the passenger'* side, it is likely a mode door issue of some sort.

If AC is selected and it is blowing warm on the driver'* side and cold on the passenger'* side, it could be a mode door issue of some sort, or it could be a bad evaporator.

Based on this, it seems like a control issue, like the control is commanding differently than it appears to be set to.

I had a mechanic tell me to check the level of refrigerant in the system.....I said, "But this the heat and not the AC"....he said, "Despite that, it can cause heater issues if it is low?".......is that true?

I have it set on 90 and it'* not blowing warm..... I used my scanner to open and close the mode door and saw it working just fine. This is weird.

This does not make sense to me. Low refrigerant would make for warmer air from the heater.