Since the IHKA w/MAX button has a higher level software...I'm not sure if there will be an issue or not if you install an IHKA w/REST button. For certain, your HVAC system will not have the MAX programming. It also probably came from an e39 if it has the REST button since the MAX feature appeared mid production on the e38 & e39 (like around 2000/2001).
As far as the other programs...more than likely there will be some retro-software functions...at least 80%-90% if not 100%.
The e38's, e39's, & e46's HVAC system also received a solar sensor upgrade around the same time that the MAX button appeared...I'm not sure how the e53 was designed...I can't recall seeing the solar sensor in any documentation for the e53's HVAC system.
{e39 IHKA's solar sensor}
{how the solar sensor functions}
