98 Corvette, heater A/C control won't change 'modes'? Fan runs fine but very little flow comes out anywhere. Can you tell me what I need to replace? Thanks. Martin

With the engine running do you have vacuum to the vacuum control switch in the heater control?

This is a malfunction with the climate control switch. The switch is electronic and will need to be replaced.

check for flow through heater core, also check mode doors

Did you check out any u tube video's ?
Corvette Blower Motor Module Diagnostics and Repair Ozzstar

Sounds like a bad actuator, the actuator is a small motor used to control a door in the heater box, there are a few doors to control temp of air and then one for mode (location of air blowing out ) and one for recir. try to locate and unplug it and replace the fuse and see if that stops the fuse from popping if it does then replace the actuator.

You may have a faulty thermostat. If its stuck closed the fan won't run. Thermostat tells the car when to turn on/turn off the fan based on how hot the engine is getting.

The mode doors are operated by vacuum. Check the vacuum supply line to verify it is connected to the intake manifold. If that looks good, remove the control panel to see if vacuum is coming to the mode switch. Then check to see if the switch is transferring vacuum to the actuator lines. Here is the panel removal procedure:

1. Disconnect the negative battery cable.
2. Remove the necessary bezel(s) in order to gain access to the control head.
3. Remove the screws that fasten the control head to the instrument panel.
4. Pull the unit out to troubleshoot.

I would take the battery cables loose and actually verify battery is not leaking. If "security" is causing no start then you can tell by watching the security lamp on dash. It should be on solid when key is turned to run if it is part of your concern. also sounds like you could have a body control module problem it controls the interior lamps which may explain clicking you heard and also controls the security.

Keep us updated.

change fan control switch on heater control panel has short