When I have my vette on vent and cool temp, the air coming in from the vents is hot. I always thought that vent meant fresh outside air at outside air temp. Now that summer is here with 90 degree temperatures, I have to put the AC on even if the tops are out, to stop the hot air comming in from the vents. (I also have the shut off valve in the heater line.) Is this normal to have hot vent air for these cars?

Sounds to me like a heater door somewhere is not closing or at least not closing all the way. However if you have a shut off valve in the heater hoses I can't imagine why you still have hot air coming in. The hot air is only coming out of the vents and not through some air leak in/under the dash bringing hot engine air into the cabin?

i also am having the same problem and have been told it is a heater door not closing all the way. will find out this weekend as working on her i am.

I wonder if the shutoff valve is actually closing? Maybe you think you've got shutoff, but actually have'nt due to a leak somewhere... when you push the lever to cold, it operates a big door inside the heater box that bypasses the heater matrix. At its full extent, a lever on said closing door pushes against a little vacuum valve (on the top of the heater box - right up under the dash) which applies suction to the shutoff valve in the heater pipe. The puzzling thing is, the hot / cold lever is attached to a bowden cable, so gives a positive connection to that door I'm talking about - so pulling it over to cold should move the door, no questions asked. Move the lever to cold with the motor running, disconnect then stick your finger over the end of the cutoff valve vaccum line. If there's a vacuum, then perhaps the valve diaphragm itself is stuffed. If there's no vaccum, then i'd suspect one of two things:
Either the little valve on the top of the heater box is not opening at "cold". In this case try adjusting the bowden cable. Do this by taking off the carpet panel on the pass. side, the cable is pretty obvious and should have a double ended screwed insert in it. It just takes slack out of the cable. Turn this either way until moving the heat/cold lever just begins to feel resistance as it enters the cold extent. (this resistance is the door pushing against the shutoff feed valve)
Option number two is that the little valve is working, but not getting any vaccum feed.I'm not sure from memory if it's fed straight from the engine, or via the a/c controls. You could try to listen for a hiss down below the a/c controller, (if you can, over the engine rumble!) which would suggest the valvey thing down there's leaking - but like i say, i can't remember if that part even feeds the shutoff valve or not.
I had mine apart a while ago, to have the leaky heater matrix soldered up. So I took the opportunity to have a look at how the vacuum lines went. Heaters are always a swine to work on, and the vette's vacuum system makes them even worse! Good luck. If you can isolate some more symptoms from what I've said, let me know and we'll see where to go.

Nice description on the heater door. It sounds like that is definately one of my problems. I am also changing out my manual heater hose shutoff valve. I think that it has not been providing a tight shutoff, and allowing hot coolant into the heater core.

FLAVETT,

Theo's description is good, and the water cut off valve vacumn switch is feed from the same source line that runs down to the ac/heat/vent switch via a T, which is located on top of the heater box near the center of the dash. I am going through the process of fixing my heat/ac system. Today I figured out how all the hoses where ran w/ the help of my assembly manual (get one if you don't already have one!). Once I figured out the routing I was able to make use of my Mighty Vac (hand held vacumn pump... can get at most parts stores) and check to make sure all the vacumn actuators were working correctly. Once I determined they were all working, I then hooked back up the ac/heat/vent vacumn switch and nothing worked???... So I took the switch apart, which consists of a little rubber disk with grooves in it to route the vacumn to the correct port, and ended up cutting out a little spacer (I used a piece of 600 grit sandpaper since it was the correct thickness I was looking for) to put behind the rubber disk. I also sanded the surface it seals against, and put a little grease on the disk and sealing surface. After putting things back together, all the vacumn actuators worked correctly according to the switch position... now to put the dash back togther.

Hope this helps you out...

aka

Yeah, I remember now... I did exactly the same thing on mine. The little rubber disc in the controller was leaking, so I gave it a clean and then put the most minute amount of grease on it to get a good seal. I suppose any grease would be suitable, as long as it doesn't attack the rubber. I used some red rubber grease that's intended for sliding rubber suspension bushes onto shafts etc - logic would say that this would be ok. It's obvious if you've fixed it, as you'll no longer hear a permanent hiss coming from under the A/C lever.. I think a bit of noise when you move the lever is ok though.