i have a corsa c and it makes a very strange hissing noise from the vents only in the cold position and a slight loss of coolant

i stumbled across a volvo forum and a member has described what is happening to mine

Heater Vacuum Controls, Source, Leaks.

Leaking Sound from Heater Controls. [John Sargent] One of my 740s made a hissing sound from under the dash in the area of the heater temperature control lever. The manual heater control assembly supplies vacuum to the under hood heater valve to shut off coolant flow to the heater core in the cold position of the control lever. The vacuum connection had come off the heater valve, and the free flow of air caused the hissing sound at the heater control. Connecting the vacuum hose to the heater valve cured the hissing sound, and shut off the flow of coolant through the heater core. See also the notes below under "Vacuum Check Valves". See instructions for help on removing the vacuum hoses at the back.

can sum1 be so generous and tell me where the vacuum pipes are eg where should i be looking, the noise had troubled me for almost a year now, been into vauxhall about 10 times and they still not fixed it, please please please