Fig. 27 — Fan Performance Using Accessory
Power Exhaust
XIII. GAS HEAT
Verify gas pressures before turning on heat as follows:
1.Turn off manual gas stop.
2.Connect pressure gage to supply gas pressure tap (see Fig. 13).
3.Connect pressure gage to manifold pressure tap on gas valve.
4.Turn on manual gas stop and set thermostat to
HEAT position. After the unit has run for several minutes, verify that incoming pressure is 5.5 in. wg or greater, and that the manifold pressure is
3.3 in. wg. If manifold pressure must be adjusted, refer to Gas Valve Adjustment section on page 29.
5.After unit has been in operation for 5 minutes, check temperature rise across the heat exchangers. See unit informative plate for correct rise limits of the heat supplied. Air quantities may need to be adjusted to bring the actual rise to within the allowable limits.
XIV. BASE UNIT OPERATION
A. Cooling, Units Without Economizer
When thermostat calls for cooling, terminals G and Y1 are energized. The indoor (evaporator) fan contactor (IFC) and- compressor contactor no. 1 (C1) are energized and evapora- tor-fan motor (IFM), compressor no. 1 and condenser fan start. The condenser-fan motors run continuously while unit is cooling. If the thermostat calls for a second stage of cooling by energizing Y2, compressor contactor no. 2 (C2) is ener- gized and compressor no. 2 starts.
B. Heating, Units Without Economizer
NOTE: The 581A155-240 units have 2 stages of heat.
When the thermostat calls for heating, power is sent to W on the IGC (integrated gas unit controller) board. An LED (light-emitting diode) on the IGC board will be on during normal operation. A check is made to ensure that the rollout switch and limit switch are closed and the induced-draft motor is running. The induced-draft motor is then energized, and when speed is proven with the hall effect sensor on the motor, the ignition activation period begins. The burners will ignite within 5 seconds.
If the burners do not light, there is a 22-second delay before another 5-second attempt. If the burners still do not light, this sequence is repeated for 15 minutes. After the 15 min- utes have elapsed, if the burners still have not lighted, heat- ing is locked out. To reset the control, break 24-v power to the thermostat.
When ignition occurs the IGC board will continue to monitor the condition of the rollout and limit switches, the hall effect sensor, as well as the flame sensor. If the unit is controlled through a room thermostat set for fan auto.,45 seconds after ignition occurs, the indoor-fan motor will be energized (and the outdoor-air dampers will open to their minimum posi- tion). If for some reason the overtemperature limit opens prior to the start of the indoor fan blower, on the next attempt, the 45-second delay will be shortened to 5 seconds less than the time from initiation of heat to when the limit tripped. Gas will not be interrupted to the burners and heat- ing will continue. Once modified, the fan on delay will not change back to 45 seconds unless power is reset to the control.
When additional heat is required, W2 closes and initiates power to the second stage of the main gas valve. When the thermostat is satisfied, W1 and W2 open and the gas valve closes, interrupting the flow of gas to the main burners. If the call for W1 lasted less than 1 minute, the heating cycle will not terminate until 1 minute after W1 became active. If the unit is controlled through a room thermostat set for fan auto., the indoor-fan motor will continue to operate for an additional 45 seconds then stop (and the outdoor-air damp- ers will close). If the overtemperature limit opens after the indoor motor is stopped within 10 minutes of W1 becoming inactive, on the next cycle the time will be extended by 15 seconds. The maximum delay is 3 minutes. Once modi- fied, the fan off delay will not change back to 45 seconds unless power is reset to the control.
A LED indicator is provided on the IGC to monitor opera- tion. The IGC is located by removing the side panel and viewing the IGC through the view port located in the control box access panel. See Fig. 28. During normal operation, the LED is continuously on. See Table 15 for error codes.
Table 15 — IGC LED Indications
| | ERROR CODE | | LED INDICATION |
| | Normal Operation | | On |
| | HardwareFailure | | Off |
| | Fan On/Off Delay | | 1 Flash |
| | Modified | |
| | | |
| | Limit Switch Fault | | 2 Flashes |
| | Flame Sense Fault | | 3 Flashes |
| | Five Consecutive Limit | | 4 Flashes |
| | Switch Faults | |
| | | |
| | Ignition Lockout Fault | | 5 Flashes |
| | Inducer Switch Fault | | 6 Flashes |
| | Rollout Switch Fault | | 7 Flashes |
| | Internal Control Fault | | 8 Flashes |
| | LEGEND | |
IGC | — | Integrated Gas Unit Controller | |
LED | — | Light-Emitting Diode | |
NOTES:
1.There is a 3-second pause between error code displays.
2.If more than one error code exists, all applicable error codes will be displayed in numerical sequence.
3.Error codes on the IGC will be lost if power to the unit is interrupted.
C. Cooling, Units With Economizer
Upon a call for cooling, when outdoor ambient is above the changeover control setting, the economizer damper moves to VENT position. The compressors and evaporator and con- denser fans energize and operate as per Cooling, Units With- out Economizer section on this page.
Upon a first call for cooling, when outdoor ambient is below the changeover control setting, the evaporator fan starts and the economizer is fully open. The compressors remain off.
