______________
Tom
71 454/365 Mulsanne Blue Convertible

Assuming all of the other HVAC vacuum operated functions work normally, I would start at the control module and treat it like an electrical problem and see where you're losing the vacuum for the heater control valve.

______________

1973 L-82 4 spd

 Tom, do the doors on the system move when you change from Defrost to A/C to heat?(Air blows out where you want it to?) If not, first thing to check is vacuum AT the control switch from the engine. If all of the doors are operating properly, and you're just not getting a vac signal at the hot water shut-off valve, then you would need to trace the vacuum line from the switch to the valve. While you're at it, make SURE that when you turn the wheel to "Heat" or "Cold", that the vacuum AT the switch for the valve is working. Many times this problem is due to the switch itself drying out, and not directing vacuum to where it should. hth

|UPDATED|4/15/2019 10:10:27 AM (AZT)|/UPDATED|


______________
Joel Adams
C3VR Lifetime Member #56    
My Link


(click for Texas-sized view!)             NCRS

"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"