It has lost some freon and is not charged correctly...the unit is pumping down and shutting off on low pressure and then after being off a bit the pressure comes up and it restarts...
Need to check the charge and top it off and you will be good to go..
If condenser is clean, and everything seems to be working fine, most likely You will have a leak of freon(very slow usually) and 90% of the chance You will need to get quote to replace evaporator coils. Watch this video, might help to troubleshoot. Hope that helps.
Possibly the defrost heater could be faulty or the defrost thermostat or defrost thermistor (sometimes called D-Sensors I believe). If you turn off the fridge and let it defrost itself for 12 hours and then start it again, it may work fine for a week or two (or may even be totally fine in case you left the fridge or freezer door open by accident).