I've read all the posts but still need some help with routing heat to the desired dash vents. I have an 89 camaro, 305 v8, carb, swapped from orig v6. Had A/C but I disconnected it. All I get is air or heat thru the defrost vent. I've hooked up a black vacuum line from intake manifold to the rotary climate control switch. Now I hear hissing when moving the temp lever to hot, no hiss when on cold. No hiss at all prior to hooking up the vac line. Heat works. I've pulled the controls out, took apart the rotary switch, lubed, reassembled. No change in symptoms. Also same with elec switch that operates in conjunction with the vacuum. All vac lines and elec lines are connected. Took dash pad off, cant see the doors, motors, or whatever routes the air to vents. Any clues or help is appreciated!

 

The default operation of the vents is in the defrost configuration. This usually happens when there is a vacuum leak that doesn't allow the controls to switch vent positions. Check all vacuum lines and make sure you have them routed correctly.

 

Upon further checking, the hiss comes from the valve/switch on the left side of the controls, where the gray and violet vac lines connect. The valve/switch rotates when moving the heat/cool lever. No hiss on cold; hisses when moving lever to hot. Does anyone know the name of this part? Also wondering about the vac motors. I see the lower mode unit (brown vac line) and the recirc unit (orange vac line). The vac lines connect to a round, flat, black unit (about the size of a hockey puck). Are these the vac motors, or something else? I've seen them described as silver top-like units, so I'm not sure what I'm looking at.

 

I had this same problem on my 88 camaro V-6 to V-8 swap. In my case it was that i had the wrong small black vac. line hooked up under the hood. There are 2 of them coming out through the firewall, one goes to the heater control panel, and the other goes to the heater control valve(which is under the hood).I had them both hooked to vac. and it caused the same problem. I would suggust that you look under the hood for another small black vac. line coming from the firewall. You may be having the same problem i had. Remember only one of them should be hooked to vac.

I think.

 

Thank you! I did find another vac line and hooked it up. Seems to be working now. I dont have a heater control valve, so one of the vac lines isn't connected to anything.