It's hard to come up w/ a scenario for 4-7 v at the compressor connector. I assume battery is good, 12.6v or thereabouts?

Some suggestions:

1) Measure voltage at compressor relay where you installed jumper. It should be 12V.

2) If you still measure low voltage, find fuse 34 in underhood fuse box and measure voltage to fuse 34. Fuse 34 is on back row nearest the firewall at the "next to inside" or 4/5 position counting from outside.

3) If you still measure low voltage, something is wrong w/ battery, battery connections, or your volt-ohm-meter.

good luck