I parked my 97 C5 for about 2 months. I didn't crank it or even open the doors, now with the temp control all the way down it blows ambient air, with the temp control all the way up it blows a little warmer than ambient. The only thing that works half way is when I put it manually in defrost. With the temp control setting as low as possible it feels slightly cooler than ambient but not cold and with the temp all the way up it feels maybe a little warmer than ambient but not much. It makes no sense HELP!!! It's not that cold in Alabama but too cold to drive it as is.

Do you have electronic climate controls?

If so, try this. Are there any codes present too?

This was taken right from the GM serv manuals.

Re-Calibrating Temperature Actuators After Power Loss

Circuit Description
The HVAC control head receives an actuator position signal from the RH and LH electric actuators. The electric actuator position sensor is a potentiometer that is tied to a 5 volt reference source through CKT 1791 and to ground through CKT 1798, both from the HVAC control head. The variable output from the potentiometer feeds back a position signal to a pull-up resistor located in the HVAC control head. This signal is used to determine the necessary drive signal to the electric actuator motor to provide the proper air mix door position. This value is stored in the Keep Alive Memory (KAM) portion of the HVAC control head.

After replacement of either the LH or RH electric actuator has been completed, reinitialization of the actuators must be performed. Reinitialization can be easily executed by removing the HVAC CON MiniFuse® #27 from the Instrument Panel Electrical Center and then reinstalling the fuse back into its proper position. When the HVAC control head is first connected to power, the system will perform an initialization routine lasting approximately 60 seconds. During this routine, both RH and LH electric actuators will cycle full travel in both directions learning the end positions. Position feedback readings are sent back to the HVAC control head and compared to a range of acceptable end readings. If during initialization the position feedback readings are not within the acceptable range, a diagnostic code will be set. If the position feedback readings reach values of 0-5 counts or 250-255 counts, the HVAC control head will then interpret the reading as a "feedback-short" or "feedback-open" condition respectively. NOTE: Feedback-short or feedback-open conditions can occur due to electric actuators being initialized while not being attached to the HVAC module case.

Is the air primarily coming out of the defrost, regardless of the settings? If so, you probably have a vacuum leak. And the most common location is below the battery as the original battery often leaked and the acid would eat the vacuum tubes.

any word? did you find a fix?

ok after getting under the dash and blowing back out the vacuum line it was obvious i have a leak. pulled the battery (again) and spotted what i had missed the first time... acid got the line in 2 spots... WHEW! way better than i was expecting

thanks for the help!