The heating system do not work ... on 2005 Volvo XC70

By morning when it's freezing, I put the heating system on "automatic" mode and set maximum temperature. I have to drive for some kilometers and normaly only after some speeding up it does start to warm the cockpit !!! However, in Summer the air condicioned works ok and it lowers the temperature very rapidly

Asked by for the 2005 Volvo XC70
seek diag and est from your mech
2 more answers , 1 more comment
seek diag and est from your mech
Have you thermostat checked, it may be stuck open, causing this problem. If this is the issue, the check engine light should come on though, is it on?
Thank you very much for caring ... actually there is no lights on seeming that evereything is ok. This happens since tthe car was brand new, since I bought it. At that time, Volvo mechanics told me that this was due to the gap between in-car and out-car temperatures ... but more and more I feel like a stupid explanation