Relay Contact Sticking Problem
Capacitors &amp; induction motors can both have HUGE initial inrush surge current transients that are often too short in duration to accurately show on most ammeters. An easy way to relieve your welding problem would be to install a 15A-20A ICL (Inrush Current Limiter) in series with your relay. ICLs are resistors with a highly negative-sloped resistance/temperature curve; this allows them to slow the instantaneous inrush current for that damaging fraction of a second, then reduce resistance &amp; effectively short after a very short delay.