Every system loses a little refrigerant through hose walls and seals. A typical car loses 8 to 12 per cent of its charge a year, which is why cooling gets steadily weaker over three or four summers without anyone noticing a fault.
A realistic interval
Every two years for a car in daily use, annually for a van, tractor or truck that works hard in dust and heat. Systems used all year round last longer than systems only switched on in July: running the compressor circulates oil past the shaft seal.
What a service should include
- Recovery, measurement and recording of the existing charge.
- Vacuum and moisture removal, held long enough to prove the system is tight.
- Recharge by weight, with the correct oil grade topped up.
- Cabin filter inspection and an evaporator cleanliness check.
- Vent temperature and pressure readings recorded before and after.
If a workshop simply plugs in and adds gas without recovering and weighing first, they cannot know what is in the system, and neither can you.