Who needs a heater valve?

[1998Exp]

You know, that all-plastic, failure-prone gizmo at the connection to the heater core behind the firewall. As it recently broke, relieving my Ex of all coolant in a jiffy and I am waiting for kind people to tell me which way to install the replacement (see my previous post on the subject), I have been contemplating the need for this thing. It closes in MAX AC or OFF to block the coolant flow to the heater core, but doesn't the blend door perform a similar function anyway? A point of reference: my 04 Crown Vic, with a virtually identical HVAC system doesn't have a heater valve.

 

[BKennedy]

The valve keeps coolant out of the passenger compartment when the heater is not being used. Without it, you can feel the heat radiating through the HVAC by the passenger's feet. You can bypass it and see how you like or don't like it with 2 pieces of 1/2" OD tubing, hose clamps, and a plug for the vacuum line. I carry 2, 3" pieces of tube in my Explorer in case the plastic valve (or heater core) falls apart. It fell apart on me before, luckily in the garage.

You install it just like the old one came off. There are arrows on the valve showing you the direction of flow. Some of the aftermarket valves don't line up right because the flow direction of wrong.