How do you replace a ( P/N:47-21604-03) high pressure switch manual reset on a Rudd model:UPJA-036JAZ heat pump?

I would cantact Rudd to see if the fitting has a schrader valve. If it does, you simply untread the old limit, and thread a new one on. If there is no scrader valve, or the limit is brazed directly into place, you will need to reclaim the refrigerant, cut the old limit out, braze a new one in place, reclaim the system, and recharge. Hope you have a schrader valve connection. Good luck, and please let me know how things work out.