We had a similar problem on our 4840. It ran 15 years on the factory compressor until it finally went out. We bought a rebuilt Deere unit and had a local shop charge it with freon. Two months later it was in JD shop for some work and a Green lite and was told the shaft seal was leaking bad and should replace the compressor. When I told them the story they seemed to just pretend it wasn't leaking and didn't fix it. The tractor leaked freon a little each year until we traded it. Was never sure if they just were looking for things to fix on green lite or if it should have been warrantee. There was signs of oil at the seal soon after it was installed.