1995 Chevy Tahoe Part name

I am trying to diagnose why i have no heat. I found that the heater control valve that lets coolant go to and thru the heater core is not opening. I need to know what the part is that sends vacuum to the valve. This part is located on the accumulator. it has a 2 wire connector going to it and one vacuum line coming out of it that goes to the heater control valve. Thanks in advance.