how does an 81 heater work? i have never seen heater hoses in a c3 engine bay and am curious as my aircon works cold but my heater has never. got any pics of how it should be hooked up???? is it something to do with that electric component in the top of the air box?

 

there are two heater hoses on your '81, or at least there should be. If your car only was driven in warm weather a previous owner may have removed them or bypassed them to keep additional heat out of the cabin.

Since you have AC on your car, the heater hose connections to the heater box are on the bottom of the box and not fun to get to with the body on the car, it's tight in there.

one hose runs directly from the heater box to a leg on the water pump. The other hose runs from the heater box to a vacuum controlled valve and than out of that valve to the intake manifold.
The vacuum control valve has a small vacuum line attached to it to open and close it via the AC/Heater control in the dash.

If the heater hoses and parts have been removed off your car it's not that big of a deal to replace them. You can get the heater hoses from any of the major parts vendors, even very possibly from your local Chevy dealer parts counter and the vacuum valve can be gotten from most local parts stores.
The intake manifold and waterpump connections had to have been plugged if your heater hoses were previously removed so just remove the plugs, install the new heater hoses and vacuum valve and hook up the valve to the vacuum line that go to thew control panel in the dash.

Here is a pic I scanned for you from my '78 AIM showing the heater hoses on a car with the AC option.

http://www.lbfun.com/warehouse/misc/172.jpg

Here are some additional pics that may help:

bottom of the heater box showing the two connections for the heater hoses:


showing the vacuum control valve on the one heater hose line:


here you can see where the heater hoses connect to the intake manifold and to the leg on the waterpump. Excuse the dirty motor, this was during disassembly so I could clean the motor up.

 

thanks barryK . thats good info and pics. i must have no heating accesories at all anymore because under there where the two pipes hang under the airbox in your picture i have nothing , just the void that goes between the firewall and airbox. im wondering if because i have had a right hand drive conversion done with a steering wheel now going through the edge of my airbox it had to get removed. there was no heater hoses or control module on my car when i got it.