We have Panasonic units, they are 7 years old. They have never been serviced, but we do clean the internal filters every quarter, and I check the outside units visually. I asked an electrician who was doing some work for me a couple of years ago, and he said as long as the temperature was okay, they were fine. He told me to use a temperature probe, to make sure the temperature of the air being pumped ( when they first start) was as set, and if so, then they were fine, and didn't need anything.we use them all winter for heating, and during July)/August for cooling.