Written on: October 14, 2024 by Timmie McElwain
As we continue looking at some of the more advanced electronic controls used on gas heating, and particularly the more advanced high efficiency equipment, it is important to understand how the controls are applied. The majority of new equipment today involves some form of electronics.
Different equipment manufacturers may have different ways of applying these controls—from intermittent pilot application to direct spark ignition and including hot surface. It is important to understand how the controls operate and not jump to conclusions without going through the operating procedures. As we continue our series on Advanced Controls for gas heating, we are going to address two-stage heating.
As many of you know, we have closed the Gas Training Institute. The eight manuals that we have used in our one-week course are still being printed and are available for purchase, and I am available for classroom training.
Honeywell ST9162 Two-Stage Electronic Fan Timers
The ST9162 Two-Stage Electronic Fan Timers integrate control of all the circulating fan operations in a two-stage gas warm air furnace. These controls are the central wiring point for most of the electrical components of the appliance. The ST9162 monitors the thermostat for heat, cool and fan demands and controls a multi-speed circulating fan as required. Communication with the SmartValve System Control initiates appliance lightoff.
The ST9162 connects to either a single-stage or two-stage thermostat. For both thermostats, it provides sequencing of two heat stages in a two-stage gas warm air appliance.
The ST9162A features a field-adjustable heat fan-on delay and a field-adjustable heat fan-off delay. Cooling fan-on and -off delay is fixed. Specific timings vary. See appliance label or instructions for timings that are available for a specific appliance.
A single-stage thermostat mode with a fixed, 12-minute, second stage delay is field-selectable. Electronic air cleaner (EAC) and humidifier (HUM) convenience terminal connections can be provided as an option. Continuous low speed indoor air circulation is also available as an option. Thermostat connections are screw terminals.
Figure 2 shows the dipswitch location and also the Y2 connection, which is for humidification.
The ST9162 can be set up for a two-stage or a single-stage thermostat as shown by the settings on dip switch 4 in Figure 3 (seen in the lower left hand corner).
In addition, Figure 3 shows the different settings for dip switches. Switch 3 is for heat fan-on delay. Switch 1 and switch 2 are for the heat fan- off delay of 60, 100, 140 or 180 seconds.
Figure 4 shows the location of connections and switches on the circuit board. Figure 5 is the diagram for the SmartValve two-stage valve with the ST9162. ICM
