A/C Problem Compressor clutch goes on/off every 20 secon

Hi! I had a problem with my 2004 MustangGT 2v4.6L Air Conditioner. The Compressor Clutch was turning on and off every 10 seconds. So I took it to the dealer and they changed the compressor to a new upgraded model under warranty (3 weeks ago) I started my car the other night and I noticed the compressor was coming on and off every 20 to 30 seconds, when the car was 1st started. It did go away after I drove the car about 5 miles and seemed like the compressor/clutch was staying engaged. I went out tonight again and upon startup had the same problem. The Ford Mechanic told me over the phone that this is a common problem until pressure builds up in the system. Mean while the A/c is working fine blowing cold air. I'm just scared the A/C Clutch will burn out due to constant on and off. Does this sound right?
PS No sign's of any oil leaks and car has only 14,000 mi on it. Not driven every day