Vette(s): #1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/
Am-Fm/map light National/Regional/Chapter NCRS "Top Flight"
#2-1985 Bright Red/Carmine Cp.L-98/auto
Member: NCRS, NCRS Texas, Corvette Legends of Texas
Prolly have a vacuum line off, possibly in the engine compartment. A more likely cause is gonna be in the control switch(es) in the console. The vacuum switch there can/will dry out over time, and create what amounts to a vacuum leak, so when you move the lever to change the "mode", there is no vacuum to pull the servo and change the door positions.
If you can get in a really quiet area, start it up, close the doors/windows, and listen around the HVAC control in the console for a hissing noise as you move the lever slowly from position to position, stopping in each position for a few seconds to allow the switch to complete the vac. circuit. If you hear a constant hiss, that will be a vacuum leak. You may normally hear a little hiss as the doors change, but a constant hiss is a leak.
You'll prolly wind up changing the control..
____________________________________ Joel Adams C3VR Lifetime Member #56 My Link
Vette(s): 70 LT1 coupe, 69 350 HP coupe, 69 390HP 427 coupe, 71 LS5 convert, 85 coupe, 93 coupe
Another common problem is the diaphragm in the actuators. There are several on an AC car. The one that leaks is always the one that is hardest to get to. On my '68. the bad one required removing the gauge cluster, right side dash, and entire heater box. Then 30 seconds to change the actuator.
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Corvette (Vette) Model Years on this site: 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982