where is heater water control valve? on 1990 GMC 1500 Pickup

I can't get hot air from the heater. I had to change the thermostat anyway and hoped that would help but no joy. Next on the list is the HWCV but the manual says it is in the engine compartment but it's not there.

Asked by for the 1990 GMC 1500 Pickup
if it has one, it will be on the paaenger side by the heater hose inlet into the core. it is vaccuum operated.