Heater core valve?

[F14CRAZY]

Howdy. I once read about 2nd gens having an electric valve on the heater core hoses, that would stop coolant flow to the core when the air con was on, since there's still a little bit of airflow going through the core. Turning off coolant to the core would result in cooler air con.

Is this simply a shut off valve on the inlet hose? (I think it's the one nearest the driver's side). Or is it more like a bypass, like a water softener? Anything will help, with it sometimes getting above 100 here in mid Michigan

 

[shamaal]

On my 91, setting the environmental control to MAX A/C shuts the vacuum controlled recirc door. I'm told on the later vehicles it also shuts off the vaccum valve on the heater line. (your question).
When you go into MAX A/C you should hear a gentle 'whump' from behind the glove box as it closes.

 

[BrooklynBay]

The plastic color coded vacuum lines dry out over time, and crack. When this happens, you get either delayed, or no movement of your vacuum controlled pistons.