Automatic Temperature Control: Components: Programmer: Notes
The ACC programmer is of a revised design. The new programmer, designated MK II, is revised in the electrical-to-vacuum transducer mechanism. Previous systems used a "force balancing" valve to provide either vacuum, vent, or closed operation with no flow at controlled (balance) point. The MK II programmer is based on the "bleed" principle, identical in concept to the temperature sensor in the thermal air cleaner and to the servo in the cruise master system.
The higher efficiency of this type of valve results in a simpler amplifier circuit as well as a more compact transducer.
With the MK II programmer, supply vacuum is metered through a 0.016" diameter hole in the vacuum relay, and the transducer provides a variable vent action which regulated the vacuum signal to the power diaphragm. Because the transducer has a high vent flow capacity, a porous metal restriction is provided in the power diaphragm vacuum feed line to maintain position of the programmer output until vacuum relay can lock at engine shutdown. The power diaphragm incorporates a vacuum level valve which is actuated by the diaphragm plate at the maximum heat end of travel to limit the power diaphragm level to approximately 6 in. Hg. This limits the programmer vacuum level, preventing possibility of locking in maximum heater under certain low engine vacuum conditions.
The revised components in the programmer are as follows;