R129 2001 SL500 A/C Problem--Please help a newbie

[kevwarae]

I have a 2001 SL500---only has 19000 miles and the A/C is acting up---dealer said no code fault---A/c will not engage when button pushed, but if I leave the button pushed and the meters showing on high (4-5 bars) the A/C will come on eventually and run a few seconds and then go off again and continue to come on and off randomly but in short burst ---- it is very cold when it comes on, so it is charged, the heat does the same thing