Found unit # 3, only heating back side element, checked switch, found when switch is bumped it would occasionally heat both elements. Needs new switch. While checking voltage trough element, a microwave door was shut causing bracket to short out on element. Fount element will now not heat at all. and rear element is only 50%. Needs elements also. 1-5-18 Removed failed heating elements and installed two new elements and left extra for spare on site. Removed failed infinite switch and installed new switch, energized and checked operation. Found no power to front side elements . Found breaker bad and wiring burnt and bare inside conduit. Replaced breaker and rewired heating elements. energized unit all operations normal.