Hi all,
I need some help if @ all possible. I have replaced my thermostat OEM type purged my cooling system and now I have to run my heater controls up to 90 before I start to get really hot heat. In auto mode it will be hot then turn off cool even with the outside temp being 30. I have to run it in manual mode. Any pointers would be appreciated.

 

Tell us more..............How did you purge? Also the "hot then turn off cool" not following that.

 

I used a vaccum and flush system with a two way valve that pulls the coolant out of the system and then fills the system with fresh coolant. When I turn set the temp to 75 it will start out blowing hot air and heat the car up. Periodically it will start blowing cool air and I will have to raise the temp. I eventually end up setting the temp on 90 and lowering the fan speed because it gets too hot inside.

 

The computer tries to maintain the temperature you set it at by reading the temperature from the thermometers (one by your legs another under the windshield). If you set it to 75º then the temperature of the air coming from the vents will start to cool when the reading from those thermometers approaches 75º. This is in order to prevent the temperature in your car from going above the desired temperature. Exactly like the thermostat in your home.

Unless I misunderstand you and your car is still cold inside when the air coming from the vents starts to cool.