Interior AC and Heat Regulation
 

Yes I did a search. :)
My heat and AC do not regulate properly, either take forever to get hot or cold or don't coincide with the settings on the control panel. My question is this. Will replacing the control panel in the dash solve this issue or are there other things to check or consider? I've checked the fit of the air intake in the engine compartment and its tight.

You may have a bad outside temp. sensor. It's behind the passenger side foglight grill and the HVAC system takes the outside temp and does the math with what your inside setting is and pumps out the appropriate temperature air. Keep an eye on the outside air temp in the cluster and make sure it's consistent with that actual outside temps. :D

Thanks, the outside air temp shown in the gauge cluster appears to be accurate. So am I back to the control panel as the culprit?

Interior temp sensors go bad as well as evaporator temp sensors.

Right, and thats the one inside the HVAC control panel on the dash, correct?

I presume the C55 is similar to the C32 in the HVAC department. If so, there are a dozen motors and vanes to control the distribution and heat levels of the air.

According to a SDS scan on my car, I have a bad motor or linkage, and find through forum searching that the levers arms commonly fail on the W203 HVAC system. The levers were upgraded to prevent breaking, and are sold as a kit. So if you do replace them, get the upgraded parts.

I have the parts to repair whatever may be wrong with mine, but it is a full day to pull everything and fix it, so I have not dove in yet.

If possible, get a scan from a local member (or buy your own) to determine if any of the motors or control vanes are not operating. A scan will show this.

This may be the cause of the issue you are having. And it will potentially find the real source of your problem that others have stated.

Keep us posted on the cure.