A convertible food service cart including a cold tray compartment and a conversion compartment, both of which are insulated and cooled by respective refrigeration systems. The conversion compartment is provided with a plurality of electrical plugs which connect in parallel and which are vertically spaced within the conversion compartment to receive electrical plug receptacles affixed to the hot food conversion trays. The conversion trays include a conductive, flat, heating element which is sandwiched between two sheets of thin, insulating material and provides uniform temperature throughout. The warm food is originally placed in the conversion compartment in refrigerated condition. An automatic programmer is provided to terminate the refrigeration action in the conversion compartment and to activate the tray heating plugs in predetermined time to properly heat the warm food immediately prior to serving.