Just finished some ac work on my 1990 240dl. Thanks to all who replied to my earlier post.I was looking at the ac clutch and noticed that it took a while to cycle off then on when the car is at 900rpm +/-. When I reved the engine a bit it would cycle on and off a bit faster.I guess I shouldn't complain because I'm now getting close to 40 degree temp at the vents. But is this the normal way the clutch works,less often on low idle and more often at higher speeds? Thanks,
Nelson

I am not an A/C expert but my understanding is that the A/C compressor is supposed to cycle on and off. On a 740, there is a low-pressure switch mounted on the side of the receiver/dryer. It turns the compressor on when the low-side pressure reaches 45psi, and off when the pressure drops to around 25 psi. At idle you may find that the pressure never drops that far (or rarely does) so the compressor will run a lot. But once it starts turning faster, the pressure will drop more and this will cause the compressor to cycle off. With the compressor not running, the low-side pressure will increase until it hits 45psi then the compressor will turn on again. And the cycle continues. I'm pretty sure the 240 system is basically the same.

So, I think what you are seeing is fairly normal.

--
Matt L. -- Cary, NC -- '91 740 wagon

Thanks Matt!I'll leave well enough alone.
Nelson