dash heater control

[jsprving]

I have an 85 honey. When using the heater control the defrost works when the button is pressed but when I press either the heat or vent button the 25 amp fuse pops. I was thinking the control switch but not sure since the defrost works. Any suggestions.

[BFlinn181]

Most automotive HVAC systems are required to default on the defrost vents setting. That might explain why it only works on defrost. Many HVAC systems are vacuum operated, so not sure why you'd blow the fuse unless it's an electric operated flap system. Evans Tempcon supplies many of the dash HVAC systems, you might look at these photos of control panels and see if any look like yours.

Evans Tempcon, Inc - Service Parts

You may have to remove the panel to see if it's identified on the back.

[jsprving]

There is electric going to a small black device with 2 connections that go to a connection in the middle of the control unit and then to the fan speed controller. The vent system is vacumn controlled which is why I am confused why pushing the defrost or vent causes the fuse to pop.

[jsprving]

Here are a couple of pics of the control unit.