Don't push hard
If it's like an '85, don't push hard on the flaps! They are closed with a vacuum diaphram that's spring loaded. (normally closed). If you push hard you will break the ends of the flaps off (sounds like the words of experience?!) That's a real booger to fix.
Check the vacuum to the diaphram. If vacuum opens the flaps then the switchover valve that sends vacuum to the diaphram may be bad. Make sure you have 11+ volts to the switchover valve. If no voltage, check CCU.