Air temperature control system for vehicles

An air temperature control system for regulating the air temperature in a room in a vehicle, comprising:

• a. means, defining a continuous path, for directing air along said path into said room;
• b. means, disposed in said path, for respectively cooling and not cooling said air in said path, in response to ON signals and OFF signals;
• said cooling means having a duty cycle defined by the proportion of time said cooling means is operating and not operating;
• c. means, disposed in said path, for adding heat to the air cooled in said cooling means;
• d. means for producing a difference signal indicative of the difference between the temperature of the air in the room and a preset temperature value;
• and
• e. feedback control means, responsive to said difference signal, for regulating the rate of adding heat by said adding heat means, and regulating the duty cycle of said cooling means, so as to continuously reduce the difference between the temperature of the room air and the preset temperature value;
• said feedback control means including:
• (1) means, responsive to said difference signal, for incrementally changing the heating rate of adding heat by said adding heat means;
• (2) means, responsive to said signal, for adjusting said duty cycle to reduce said temperature difference, when said heating rate is less than a predetermined low heating amount;
• and
• (3) heating rate decreasing means for incrementally decreasing said heating rate to below said predetermined low heating amount;
• said heating rate decreasing means including means for incrementally reducing said duty cycle when said heating rate is above said predetermined low heating amount so as to increase said temperature difference, thereby to cause said incrementally changing means to decrease said heating rate toward said predetermined low heating amount.