Troubleshooting 85GT Heat Problem

[carhopper]

I started looking at the heat problem in my 85 GT AOD/CFI. I decided to start with tracking down the vacuum to ensure that the valve is being actuated. There is a vacuum rail on the drivers side fender that has a vacuum feed on a red line. I pulled the line with the engine running and no vacuum, so I back up to this little attached device and it's good coming in. I pulled the device and I can't suck or blow in either direction. I have to believe this isn't normal. I had a reducer that I had used for a blow off valve on another car and put it in line and now I have vacuum. Unfortunately the heater still doesn't work so I need to move to the next step. Any help or vacuum diagram would be helpful.

Should I order a replacement for this little thing or is it not necessary?

 

[mustangmutt]

That is the Vacuum check valve and it is needed. You should be able to suck through it one way and not the other. Make sure you put the manifold vacuum on the side you can suck on. With out it your airflow will change to the defrost under load. I think there is a Vacuum connector behind the glove box that has all of the hoses going to it. I would look there to make sure you are getting vacuum to the connector. If you have vacuum there you probably need a vacuum mode switch on the control head. Or have a leak between the connector and the controls.

 

[mustangmutt]

On my 90 the vacuum that feeds the climate controls comes in on the passenger side where the a/c fittings and heater hoses go through the firewall.