J's Nest

The heater in my 87 is not putting out any hot air. I checked the heater water control valve and found if I remove the vaccum tube the valve opens, the coolant circulates through the heater core and I have hot air. As soon as I reconnect the vaccum hose it shuts off. To me this means the valve is working, there is no blockage in the heater core and my problem is somewhere else. The control panel seems to function fine in auto or manual and it switches to A/C ok. Any ideas where I should look?

Thanks........

floridamale

Dose the control open the vents on floor bi level & defrost ok, If not try the check valve it’s located on drivers side near dizzy it’s a T valve it dose supply vacuum to the heater controls, and cruise control, connects to source at plenum. It might be a place to start the vac line is a small hard plastic one that runs into the main loom on firewall bottom of T valve.

rodj

Obviously you have vac available because the vac is closing the valve when you reinstall the line .
One of two things
The controller unit under the dash that operates the vac to the valve must be locked in the open position giving full time vac to the valve and keeping it closed.
Or the controller is not getting a signal from the head unit .

Under the dash there is a black box , approx 5 x 4" that has all the vac lines to the A/C pots coming from it; also has a large elec plug.
Inside are elec operated valves that control the vac