Opel Vectra Climatizer

Hello everyone:

I have an Opel Vectra B of the year 2000 with air conditioner, the problem I have is that it costs a lot to heat the heating. The car rises as a temperature as always and jumps the electrventilator at its normal temperature. I have downloaded the workshop manual of this car and I have seen that the heating tap of this car seems to work with a depression valve.

I would appreciate that please someone explain how it works.

All the best.