Recently developed a slight drone over the engine revs, but only when air-con is switched on.
Had the unit serviced and re-gassed yesterday (specialist I've known for many years) mileage now 51k.
Needed PAG oil to the compressor, which has almost cured the problem (it still occurs spasmodically on tick-over when it's hot outside say +80F).
However the dreaded fan blight may have struck me, as it is apparently only operating on the high speed) I'm told by the technician, (not a River specialist).
In parallel my mpg has recently dropped about 10%. I presume because the fan is cutting in on high, and reducing the engine temperature below optimum, and also must take more energy to run anyway?
I think with a late Dec. 54 reg, I only have (had) a 2 speed fan anyway?
Does the said fan only cut in with air-con on at high speed only?
Could the other speed still be there for engine cooling anyway, and is still operating, and is there a way to find out?