Engine Hunting With A/C On VN

[Evman]

It only happens every now and then, and travelling maybe 40-50km/h, but with the A/C on the engine hunts through the revs. Does this mean it neads re-gassing, or is it just on it's way out? It's in a VN, and we've had the car for 10 years now and I don't remember ever doing anythin to the A/C.

[accentstencil]

I'm not sure what you mean by hunting but a regas is only necessary if your A/C isn't blowing cold air.

[Don Sutton]

Hunting is a rythmic rising and lowering of revs similar to older diesels at idle. This is no likely to happen with the A/C on as the compressor only comes on to maintain refrigerant pressure and would be fairly random.
If engine speed changes with the A/C on and at no other time then possibly when the compressor cuts in it is taking more power to drive than normal and may be seizing possibly because the oil has been lost. You should be able to tell with the engine rpm slightly raised equivalent to that at the speed where the condition occurs with the transmission in neutral and see if the engine rpm is stable. If it is, switch on the A/C and repeat the test. There should be a small drop in rpm as the compressor cuts in and engine rpm will rise slightly when it cuts out. If the engine labours when the compressor cuts in get it checked out by an Aircon repairer.

[Evman]

Thanks Don, appreciate the help.