65 300 not switching to defrost

[74delta]

Just noticed today the heat doesnt switch over to defrost. Not 100% sure where to start. Sounds like something is going on when I press it but doesnt switch over. Any advice or common problems would be appreciated.

 

[Davea Lux]

Just noticed today the heat doesnt switch over to defrost. Not 100% sure where to start. Sounds like something is going on when I press it but doesnt switch over. Any advice or common problems would be appreciated.

The defrost function is operated by the push button for defrost on the control, the vacuum switch routes vacuum to a vacuum motor mounted on the top of the heater box. This moves a baffle door to direct air to the defrost plumbing. There are several reasons the defrost function might not be working. If the vacuum switch has an internal leak, the vacuum does not get to the motor and the switch will need to be replaced. The vacuum hose to the vacuum motor has failed and the leak has disabled the vacuum motor. The vacuum motor itself had failed and if so it would need to be replaced. Disconnect the vacuum hose from the vacuum motor to see if vacuum is getting to it. Another common issue is that the defrost door has stuck shut, check to be sure it can move freely. Photo of the layout of the heater box below, click on mail not the icon.

Dave

 

[74delta]

Well that's insanely helpful thank you so much. This all looks to be in the box behind the ash tray area of the dash correct?

 

[Davea Lux]

Well that's insanely helpful thank you so much. This all looks to be in the box behind the ash tray area of the dash correct?

Yes

 

[Gerald Morris]

FWIW, I solved this problem for now by disconnecting the vacuum motor and putting a little handle on the shaft it rotates, thus enabling me to open the defrost vent door when I want it to blow/ Admittedly, this only seems feasible on 1966 and 65 heaters and dashboards, but its really quite easy, and I've kept all the parts in case I am blessed with a new vacuum switch that will connect to the 4 front buttons. (heat only system) You may try this for the sake of getting the defrost to work quickly. Its served me for 3 years thus.

 

[74delta]

FWIW, I solved this problem for now by disconnecting the vacuum motor and putting a little handle on the shaft it rotates, thus enabling me to open the defrost vent door when I want it to blow/ Admittedly, this only seems feasible on 1966 and 65 heaters and dashboards, but its really quite easy, and I've kept all the parts in case I am blessed with a new vacuum switch that will connect to the 4 front buttons. (heat only system) You may try this for the sake of getting the defrost to work quickly. Its served me for 3 years thus.

I ended up looking down there and seems the system has been messed with. Most of the rods are disconnected but when I push the different settings the rods move around. Anyone know where I can get a diagram so I know what solenoid goes to what function?

 

[74delta]

FWIW, I solved this problem for now by disconnecting the vacuum motor and putting a little handle on the shaft it rotates, thus enabling me to open the defrost vent door when I want it to blow/ Admittedly, this only seems feasible on 1966 and 65 heaters and dashboards, but its really quite easy, and I've kept all the parts in case I am blessed with a new vacuum switch that will connect to the 4 front buttons. (heat only system) You may try this for the sake of getting the defrost to work quickly. Its served me for 3 years thus.

You wouldnt be able to take a picture of the one you rigged would you? I'm not sure wich one it is