It could definitely be electrical in nature. I've got some Gremlins running around in the system. Cruise is schizo and when plugged in will periodically give me the clickity clack crap from the actuator. High beams absolutely refuse to work. They work in "flash" mode (pulling on the stick) so it's not the lights themselves or the wires, but they will not turn on for driving. In fact I lose all of my headlights when I try to push the stick forward for high beams. Running and tailights stay on, headlights take a nap. Probably a combi-switch issue.

Anyway, when this happens the heat blows out the center registers too. I may be wrong but I think when the ACC is set to high heat the air only comes out the side registers and the floor. When this happens it blows out full bore from all the registers. And yes, it's serious heater core air, significantly and noticeably hotter than even the 95 degree ambient air outside. Setting the wheel to MIN makes no difference the only way to make it stop is to hit O and restart the system after several minutes.

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'84 300D Turbo Black w/Tan (104k)
'94 GMC K1500 Z-71 (198k)
'96 Ford Explorer V8 AWD (178k)
'51 Ford 8N ( about 2000hrs)
'98 English Setter "Jade" (10k foot weary, bird finding miles)