XIII. OPERATING SEQUENCE
A. Cooling, Units Without Economizer
When thermostat calls for cooling, terminals G and Y1 are energized. The indoor (evaporator) fan contactor (IFC), com- pressor contactor no. 1 (C1) and
When the thermostat is satisfied, C1 and C2 are deener- gized and the compressors and outdoor (condenser) fan motors (OFM) shut off. After a
B. Heating, Units Without Economizer
When the thermostat calls for heating, terminal W1 is ener- gized. In order to prevent thermostat
C. Cooling, Units with EconoMi$erIV
When free cooling is not available, the compressors will be controlled by the zone thermostat. When free cooling is avail- able, the
For EconoMi$erIV operation, there must be a thermostat call for the fan (G). This will move the damper to its mini- mum position during the occupied mode.
Above 50 F
If optional power exhaust is installed, as the
If
Damper movement from full closed to full open (or vice versa) will take between 11/2 and 21/2 minutes.
If free cooling can be used as determined from the appropri- ate changeover command (switch, dry bulb, enthalpy curve, differential dry bulb, or differential enthalpy), a call for cool- ing (Y1 closes at the thermostat) will cause the control to modulate the dampers open to maintain the supply air tem- perature set point at 50 to 55 F.
As the
D. Heating, Units With EconoMi$erIV
When the room thermostat calls for heat, the heating con- trols are energized as described in the Heating, Units With- out Economizer section. When the indoor fan is running, the economizer damper moves to the minimum position. When the indoor fan is off, the economizer damper is fully closed.
SERVICE
WARNING: Before performing service or mainte- nance operations on unit, turn off main power switch to unit and install lockout tag on disconnect switch. Electrical shock could cause personal injury.
I. CLEANING
Inspect unit interior at beginning of each heating and cool- ing season and as operating conditions require. Remove unit top panel and/or side panels for access to unit interior.
A. Main Burner
At the beginning of each heating season, inspect for deterio- ration or blockage due to corrosion or other causes. Observe the main burner flames. Refer to Main Burners section on page 37.
B. Flue Gas Passageways
The flue collector box and heat exchanger cells may be inspected by removing heat exchanger access panel (Fig. 4- 6), flue box cover, and main burner assembly (Fig. 10 and 11). Refer to Main Burners section on page 37 for burner removal sequence. If cleaning is required, remove heat exchanger baffles and clean tubes with a wire brush.
Use caution with ceramic heat exchanger baffles. When installing retaining clip, be sure the center leg of the clip extends inward toward baffle. See Fig. 37.
C. Combustion-Air Blower
Clean periodically to assure proper airflow and heating effi- ciency. Inspect blower wheel every fall and periodically during heating season. For the first heating season, inspect blower wheel
To inspect blower wheel, remove heat exchanger access panel. Shine a flashlight into opening to inspect wheel. If cleaning is required, remove motor and wheel assembly by removing screws holding motor mounting plate to top of combustion fan housing. The motor and wheel assembly will slide up and out of the fan housing. Remove the blower wheel from the motor shaft and clean with a detergent or solvent. Replace motor and wheel assembly.
D. Evaporator Coil
Clean as required with commercial coil cleaner.