M-Series Technical Manual
35
Cambridge Engineering, Inc.
OPERATING INSTRUCTIONS
OPERATING SEQUENCE
POWER ON
1. Control transformer energized.
2. Operator must select “SUMMER
VENTILATION” or “HEATING” mode.
SUMMER VENTILATION MODE
1. Mode switch in “SUMMER VENTILATION”
position.
2. Optional TSS Controller schedule calls for ventila-
tion.
3. Optional motorized inlet or discharge damper
opens.
4. Blower motor starts.
5. Unit continues to run until turned off.
HEATING MODE
1. Mode switch in “HEATING” position.
2. Thermostat or interlock calls for heat.
3. Optional motorized inlet or discharge damper
opens.
4. Blower motor starts.
5. Low airflow switch closes.
6. Entering air thermostat closes when inlet tempera-
ture is below setpoint after the prepurge delay.
7. Igniter warm up timing.
8. Gas valve opens.
9. Burner lights.
10. Igniter is de-energized.
11. Low Fire Start is de-energized after 15 seconds.
12. Unit runs and modulates until operating thermostat
and/or interlock opens (heater shuts off).
13. Steps (2) through (12) repeat themselves automati-
cally as necessary.