sparky77

Started playing with the heater and AC this week,the fuse kept blowing,it was the AC compressor I have that disconnected now.When I turn the AC on I'm getting very little air out of the vents or the defroster .When I turn the heat on it blows on the the floor just like it should but not out of the defroster. So is there a common problem with 77 C3s or is there something I could look at that will trace the problem .


Thanks,Pete

Rotonda

Pete,

You need to do more investigation. Your problems may range from electrical to debris (leaves etc.) clogging your intake to problems with the system's doors & bypasses (rather vacuum or mechanical).

I suggest that you first determine whether your system's fan produces multiple speeds (the 'electrical' problem). If not, do an advanced search on the Forum looking at fan or blower or defroster fan speed. The fix is usually neither expensive or difficult. After this, things get more involved.

As a resource, look at the Willcox Corvette site. They have a lot of info under their tech help tab that may help

sparky77

Thanks, the fan works at all speeds checked that,will go to Willcox and read ,see what could be the problem.

sparky77

The temp switch works air temp goes hot when it's slid over to hot cool when over to cold ,the blower works,I get a lot of air out of the bottom vent .I'm not getting any air out of the vents up high or the defroster any ideas.Is there a common problem with 77 vettes .

Thanks,Pete

MajD

Pete,

As I recall, there are two separate pathways for the air out of the cabin heater box. These pathways are determined by a vacuum controlled flap at the box outlet. One path directs air into a large central vent connected to the side and top center vents. This is the outlet shown in the picture below.



Note you can see the flap I'm referring to as well. It is blocking the airflow to the path described above and a spring in the vacuum actuator returns it to this default position when vacuum is removed. In this configuration, air is actually flowing out the left side of the box into a second box (described below). The actuator that controls the flap is located on the side opposite the hole you see, between the box and firewall. You will probably have to remove the box to get to it.

The second flap position directs the air into another box attached to the cabin heater box outlet. This second box also has a vacuum controlled flap that diverts the air either through the floor vents or the defroster vents. Here's a picture of that box:




The two holes on the right connect it to the other outlet of the cabin heater box. That should help you locate it. The linkage and vacuum actuator are located to the left, like in the picture. The default position for this flap passes air through the floor vents.

It sounds like both of these flaps are not working (simultaneous default positions would divert air through the floor vent regardless of switch settings). With the car running, switch the control to defrost and see if the position of the linkage on the second box has changed. If not, then disconnect the vacuum line and use a rubber line to apply vacuum with suction. If the actuator moves, the vacuum line is leaking, if it doesn't move then the actuator is bad.

If the linkage moves with the car running, then your defroster vent is blocked. The vent comes out of the top of the box and is fastened to the firewall near the top of the outlet duct. Of course, all of these things will be difficult to get to, but the actuator should be fairly easy to observe.

You could also check the flap in the cabin box in a similar manner, but the actuator is very difficult to get to without removing the box from the firewall. Good luck and I hope this helps.


MajD

sparky77

Found the problem today it is the hot water turn off switch on top of the heater box the supply vac goes thru a 3 way from the engine side one goes to the dash control one goes to the heat switch. I had no vac at the control until I blocked the supply to the switch. Now everything is working just have to replace the control .

Thanks,Pete