CPR question

[cretan]

While the compressor was running,I turned the CPR valve adjustment all the way counter-clockwise and the pressure did not drop.Shouln't it go to zero?

[Andy W]

No, first of all check on the label what the range of the valve is, the valve is used for throttling back the suction pressure after defrost or start up or to even reduce the load on the compressor to reduce the starting amps, I switch the compressor off so the suction pressure rises before I carry out my adjustments, but check your label first, it may not even be a 0 - 80 psi valve, could be a 20 - 100 in which case the valve will not let it achieve 0 psi.