4.9 LOGIC CONTROL DETAILS - CONTINUED.
Lethal voltage levels are used in operating the FDECU. Be sure to observe
extreme caution when accessing pc board with power connected. Injury or death
can occur if personnel contact any electrical terminal while the unit is connected to
Operating the system components in the manual mode will override the safety
features of the pc board and could cause equipment damage if components are
operated improperly. Use great care when operating in manual mode to consider
which components must be activated to simulate various operational modes to
prevent equipment damage.
4.9.4 Manual Override of Logic Control. See figure 4-9. For troubleshooting purposes it may be helpful to override the
automatic control of the pc board logic circuits and operate the system components manually to observe the function of
the light emitting diodes (LED's) and check for operation of the individual system components. With power applied to the
FDECU and no operating mode selected, put the pc board into the maintenance mode by placing switch number 8, on the
dual inline parallel (DIP) switch S3, down (ON). Use a non- conducting probe such as a plastic or wooden toothpick to
move the DIP switches. When in the maintenance mode, the other DIP switches can be positioned down (ON) to activate
various system components as follows; RV (7) reversing valve, RH 2 (5) electric resistance heat bank 2, RH 1 (4) electric
resistance heat bank 1, BLOW (3) inside blower, COMP (2) compressor, and FAN (1) outside fan. LED's D31 through
D35 will indicate in binary code the terminal point number on TP1 where the feedback signal is being indicated for each of
the component contactors being activated. See table 4-3 to convert the binary code to a numeric value. After operating in
the manual mode, be sure to place all DIP switches back to the up (off) mode. Failure to put the DIP switches in the off
mode will prevent the safety circuits from protecting the components and could cause equipment damage.