air conditioning problem please help

I changed over my airconditioning system to the new freon r134a or what ever and should have just done it myself. It was working fine but is slowly getting worse and worse. I had the local shop check and see if it was leaking and they said that the pressures were good. When it had the old poa valve and old drier the compressor whould run the whole time, but now the compressor would kick in and out like every 5-10 seconds and would only be cool for during those 5-10 seconds. Now it kicks in and out like every second and isn't cooling at all. What causes the compressor to cut itself off? What would cause all of these changes just because I changed over the poa valve and drier. My local shop said that the compressor shutting off and on was normal and called it "cycling" , but it never did it before, and the airconditioner worked perfect. I think they are full of bull because ever since they put it in it hasn't worked right.

Thanks in advance

Most likely, the shop has put too little r134a in the system, and the low pressure shut off switch is causing the clutch to cycle.

r134a doesn`t cool quite as well as r12. It`s about 3 degrees warmer.
By using less r134a, it allows them to achieve less pressure on the low side.
This will give you colder evaporator tempurature, but can cause the clutch to cycle more often.

To reduce the cycling, You could just add some r134a to the system to raise the low side pressure. it may not be as cold but it might be less anoying.