2003 Silverado Automatic Temperature Control?

We have a friend with a 2003 Silverado. His automatic temperature control has dual zones. Regardless of what temperature is selected on either the driver's side or the passenger's side the temperature fluctuates from absolute hot to icy cold. Sometimes the zones are synchronized and other times one side will be hot and the other cold. Anytime the truck is running there is no rhyme or reason as to when it switches or what it switches to.





In desperation, we have attempted to re-learn the actuators and access any codes (with a Snap On scanner). There are no codes of any kind.





Recent repairs include alternator, battery, and blower motor resistor, but I believe this problem preceeded those replacements.





We do not have access to a Tech 2, so any suggestions that include the use of one won't be of much help.





Thank you2003 Silverado Automatic Temperature Control?
Not sure if this will help, but it is worth a shot.





Vehicle: 1999 - 2004 Chevrolet Silverado 1500 4.3L


1999 - 2004 Chevrolet Silverado 1500 4.8L


1999 - 2004 Chevrolet Silverado 1500 5.3L





Symptom: Hot air only from the heating ventilation and air conditioner (HVAC) system after replacement or repair of an HVAC system component. Automatic air conditioning system only.





Problem: The Air Mix Valve Actuator needs to be recalibrated.





Test %26amp; Fix: The HVAC system will default to blowing hot air when the system has lost battery voltage or if the Air Mix Valve Actuator has been commanded to move without being correctly installed in the HVAC case first. Any one of the above conditions will require the Air Mix Valve Actuator to be recalibrated. To recalibrate the Air Mix Valve Actuator, start with the Ignition Key removed from the Ignition Lock Cylinder, disconnect the negative battery cable and touch the negative cable to the positive. Reconnect the negative cable to the battery. Place the Ignition Key in the lock cylinder and turn the key to the key on engine off (KOEO) position for a minimum of 40 seconds. Turn the key off. Now start the engine and check for proper operation of the HVAC system. NOTE: If the Air Temperature Actuator had been operated with the Air Mix Valve Actuator disconnected from the heater case and temperature door, it will be necessary to supply power and ground to the Air Mix Valve Actuator in order to activate the motor to center the actuator before reinstalling it on the heater case. After reinstalling, follow the procedure above to recalibrate the actuator.