A/C compressor works only when jumped

1. Swap the relay with a known working one. You can also bench test it with a multimeter, but this way is easier.

2. Check for power at the fuse. The control unit may be coming on, but there's a chance it's not sending signal to the relay.

3. The pressure switch isn't an on/off switch, so jumping it will do no good. It's based on resistance, and the particular resistance is determined by the actual pressure in the system. Too high or too low and you won't get clutch engagement.

4. Just because the system blows cold when you jump the clutch doesn't mean the pressures are within spec. You need to get a manifold gauge and see what pressures you're operating at. The little plastic gauges on the DIY cans are comically bad, get a good set or take it in to a good shop.

It's more than likely that you have a leak somewhere in the system that's caused your pressures to fall out of range. DIY AC service is difficult. You need access to manifold gauges, a vacuum pump, and potentially even a recovery system. Releasing R134a into the atmosphere is a huge no-no, and if it gets on your skin you're looking at some pretty serious frost burns. The D2 has a very basic AC system that can be serviced by pretty much any shop, and with it being the middle of the summer I'm sure you can find plenty of deals for an "AC Tune-Up". I vote that you take it in and have them figure out what's wrong.

Keep in mind that replacing the high side line isn't a DIY job unless you have access to some fairly advanced AC service equipment. You'll need to hook the system up to a pump to evacuate and recovery the old refrigerant and then after you replace the part you'll need to to create vacuum in the system to remove air and moisture before you can fill it back up.

While R124a isn't likely to destroy the ozone, it's still stored in the system under high pressure and releasing it into the atmosphere can still cause frostbite and even asphyxiation if you're doing it in a garage or enclosed space where the gas can settle. I'd recommend the evacuation and recovery be left to the professionals.

Harbor Freight sells a well reviewed AC vacuum pump that you can use to remove air and moisture out of the system yourself after the line replacement. It's only $17 and would save you the trouble of taking it in to get it refilled. However the air requirements are pretty high so you'd need a fairly large compressor.