Heater not heating at Highway Speeds

[janschutz]

I have a Classic Auto Air system in my 68 Coupe. I have had it 2 years. Coming back from the farm yesterday, the outside temps were below 30. While I was in the city with stop and go lights, the heater was fine. But when I was on the highway, the engine temp would drop and the heater would get just warm. I did not notice this behavior last winter. I am thinking that maybe the thermostat is stuck open. What do y'all think?

 

[AzPete]

That or the wrong temp. thermostat....are the heater hoses real hot? No air in the system? Is the inner door operating full range? Did you have the window closed....? lol Cable adjustment slipped from install. The a/c works on defroster I believe......

 

[guruatbol]

My woek truck which is a Ranger, only heats up when moving sometimes, just started it now that it is super cold!

Mel

 

[dodgestang]

Sounds indicative of no thermostat...or malfunctioning one.