Climate Control System Question

[Bill O']

I have a '90 LS 400 with 300,000+miles. With the A/C "off", the temperature button set to "65", the air intake button set to "outside air", the fan speed set to "medium," and the airflow set to "bi-level", I get air from the vents that is warmer than the outside air temperature. If I increase the temperature button to "85", I get hot air as expected but I can't get cool outside air to to flow into the passenger compartment. I suspect the heater core valve may not be closing completely. How big a deal is it to confirm this or is there something else I should be looking for?

[wwest]

The airflow reheat "blend" door/vane inside the plenum has a cable that operates the hot water control valve in the engine compartment. Located in the center at the top of the firewall. It should cycle from full closed to full open as you move from max cool to max heat.

In the summer I often remove the cable from the valve and simply tie it closed so no hot water at all flows to the A/C system.

[Bill O']

Thanks very much for the info!