Chrysler Repair: a/c compressor and pressure relief valve, pressure relief valve, compressor clutch

Question
after a locked up compressor and broken belt i have had compressor replaced 2 times in last 48 hrs. it holds a charge, no leaks but under higher than idle rpms the high pressure relief valve blows off!. the repairman is stumped  but he has stated theres no blockage and all pressures going in and coming out are where they are supposed to be. they already have drained oil and replaced and recharged but with same results. now they are talking there may be a blockage? what causes the high pressure relief valve to open and is it mechanical or electrical? if so can the electrical current be traced as to why its requesting opening the relief valve?  

Answer
Hi Bryan,
I have very little experience in A.C. systems. You didn't mention what year or model of Chrysler you have so I looked at the Sebring manual for '95 and found that in that one there is a combined low and high pressure cut off switch. It appears that the spec is set to cut the circuit to the compressor clutch whenever the pressure is either too high or too low. It is a simple mechanical/electrical set of switches so my first thought would be to verify that the switch is not off-value by using a calibrated pressure gauge to verify that the cut off is for valid reasons. If it is, then I don't have any specific ideas as to why.
I wish I could offer more but if the shop seems competent you may have to go along with them.
Roland