The blend door accuator might be stuck in the cold position, you will want to do the following test.
Jim, I can hear the blower air changing sounds when I move the heater temp from cold to hot so I think the blend door actuator is working. Is there a control valve controlling the coolant flow through the heater core? Ken
Try the following test.
The Automatic Temperature Control (ATC) system can be diagnosed two ways. The scan tool (DRB) can be used, or the vehicle's own control head display may be used.ENTERING DIAGNOSTIC MODE The control head can only be placed into the diagnostic mode while the engine is running and the vehicle is not moving. Set the control to a 75°F. setting (so there is no confusion with 23-36 Diagnostic Trouble Codes).
To place the system into it's diagnostic mode, press and hold the floor, mix and defrost buttons (at the same time). The ATC head display will begin to blink. When the control head display begins to blink release the floor, mix and defrost buttons. Once the control head enters diagnostic mode, the display on the control head will continue to blink. This occurs until it completes its tests and calibrations. Then it will display any diagnostic trouble codes that are present in the Body Control Module (BCM) . If there are no diagnostic trouble codes the system will return to its normal operation as indicated by temperature display.DIAGNOSTIC TROUBLE CODES
Diagnostic trouble codes related to the ATC system will appear on the display in numerical form. The diagnostic trouble codes are stored in the BCM and diagnostic trouble code numbers can range between 23 and 36. The control head can only show one diagnostic trouble code at a time. Under certain circumstances more than one diagnostic trouble code could be in the memory To scroll through any additional diagnostic trouble codes, press the panel button.