1994 Fleetwood

My mother has a 1994 Fleetwood.  The heater doesn't heat up until you have driven ther car about 30 minutes.  I have put a new thermostat in it and checked the fluid level.  Also, I don't even get cold air although I hear the fan running, nothing improves the 30 minute wait, any suggestions?

Check mode door, ambient sensor or hot water valve.

Thanks for your response, however, I don't know where these devices are located but will look them up in my manual.  Best regards, DDUE.