I had a heat pump installed about a year ago. It came with one free service and the installing company has been calling me almost every week to come out and do the complimentary tune up. I know that I obviously should take a free tune up, but it made me wonder. How often do I actually need this done? What are they actually “tuning up”?
Not an expert but these systems are fairly self-contained and robust. A few things that can be checked easily is that the fan spins, the radiator is free of debris and some compressors might have a sight glass for the oil level.
Any other checks regarding performance of the system, leaks and refrigerant level require you to perform a full refrigerant discharge and recharge. That takes special equipment and some time so no one in their right mind would do that for free, unless they can then force/guide you into some kind of upsell situation.
Larger systems might have some kind of oil filter/catch-can that you might be able to check easily but I’m not too sure on that.
After all heat pumps are just plain old A/C units with a reversible cycle.
The only other thing that comes to my mind is if you have a pump with water/sole you should check the pressure from time to time to detect leaks.