Did you check the fuses, relay? You said the lines are holding pressure, did you check the pressures with a manifold gauge? Do you have enough pressure to close the low pressure switch to power the clutch coil?
You need to figure out if the problem is pressure related or electrical. If you have a test light or a VOM, see if you have power going to the low pressure switch and across the low pressure switch. Check the high pressure switch too. Then see if you have power going to the clutch coil. Check the ground also. Make sure all your electrical connecting plugs are clean and tight. You really need a set of manifold gauges. You need to make sure there is enough system pressure to operate the A/C. The gauge you used to check pressure with will only show low side pressure, and not accurately at that. You need to check the high side too. When the system is off, the pressures should be equalized. If your high side pressure is too low, and low side,(leak) then your total system pressure will not allow your pressure switch contacts to close and power your clutch coil.
