Frankly it sounds like the AC system is undercharged and cycling too often. If you look down at the compressor under the hood, see if you can see it turning on and off also. If it is doing that you will feel the rpms change and it will cycle the fans too.
Thanks, XXXXX XXXXX the the AC system again fully today and said it was ok, I'll have a look now...
You should be able to see the clutch plate start and stop turning on the very front of the AC compressor.
Sorry, I can't see the front of the AC compressor. I can hear a clicking sound each time the fans come on. They start up as soon as the AC is switched on, then run for 5 seconds off for 5 seconds etc all the time. If the AC is properly charged should this happen or does it indicate there is a definite problem? I am pretty sure the front cooling fans didn't ever used to come on like this - i used to use the AC all the time and have had the car for 8 years. I noticed a difference in how it felt when driving fisrt time out after the new compressor had been put in.
The cooling fans and the AC compressor are controlled by the same switches, so when one comes on, the other does also. If the system is undercharged then it will go too low in very short order and then switch back off, pressure goes back up, so it switches on, and the cycle continues. Unless the pressure switch has failed and is making intermittent connection, which is the only other thing that would do that. I just can't understand why the shop says it's normal, unless they are not familiar with newer AC systems.
Perhaps it would be a good idea to take it to another shop and let them have a look. If they say it needs to be charged then let the original shop deal with it from there. The biggest problem is that running it undercharged will ruin the new compressor in short order so you can't keep going like that.
Thanks very much for that advice. I'll get it checked elsewhere.