Fig. 32 Ð Condenser-Fan Adjustment
Initial Check
IMPORTANT: Do not attempt to start unit, even mo- mentarily, until all items on the Start-Up Checklist and the following steps have been completed.
1.Verify unit has been installed per the Installation section of this literature.
2.Certify that all auxiliary components (sensors, controls, etc.) have been installed and wired to the control boxes per these instructions, the Controls and Troubleshooting literature (DK,DY,NB,NP units only), and the unit wiring label diagrams.
3.Verify that pressure hoses (static, duct, etc.) are properly attached, routed, and free from pinches or crimps that may affect proper control operation.
4.Set any control con®gurations that are required (®eld- installed accessories, etc.). The unit is factory con®gured for all appropriate factory-installed options with the ap- plicable controls programmed to the default values. See unit Controls and Troubleshooting literature for appli- cable con®guration values.
5.Enter unit set points (if applicable). The unit is shipped with the set point default values shown in the Controls and Troubleshooting literature (as applicable). If a dif- ferent set point is required, change per the example shown under Set Point Function section in appropriate unit Con- trols and Troubleshooting literature.
6.Con®gure schedule subfunctions (if applicable): occu- pied, unoccupied, and holiday periods. See Schedule Func- tion section in Controls and Troubleshooting literature for details on setting periods.
7.Verify that control time periods programmed meet cur- rent requirements.
8.Check all electrical connections to be sure they are tight.
START-UP
General
1.Put the ON/OFF switch in the ON position. Close the con- trol circuit breaker (CCB), which will energize the con- trol circuit and the crankcase heaters.
2.For PIC and VAV units, refer to Controls and Trouble- shooting literature for quick test details.
3.Complete Pre-Start-Up section items and Start-Up Check- list.
Operating Sequences Ð Base unit operating se- quences are presented below. Refer to unit Controls and Trouble- shooting literature for details on VAV and PIC controls op- eration.
COOLING, UNITS WITHOUT ECONOMIZER Ð Unit power on, system selector switch set at COOL or AUTO. position, fan switch set at AUTO. position.
On a call for cooling, Y1 on the thermostat subbase closes, energizing compressor no. 1 as ®rst stage of cooling. (Com- pressor no. 1 is always the larger of the 2 unit compressors.) If cooling load cannot be satis®ed with only ®rst-stage cool- ing, Y2 on the thermostat will close, energizing compressor no. 2.
Condenser fans are energized with compressor no. 1. The no. 1 fan runs continuously while the unit is on mechanical cooling; the no. 2 fan is cycled on and off in response to outdoor ambient temperature for head pressure control. Check cooling effects at a setting below room temperature. Reset thermostat at a setting above room temperature. Compres- sors will shut off.
HEATING, UNITS WITHOUT ECONOMIZER
48 Series Low-Heat Units Ð Unit power on, thermostat sys- tem switch set at HEAT or AUTO. position, and fan switch set at AUTO. position.
First-stage thermostat (W1) calls for heat. Time-delay re- lay (built into constant volume control board), controlling evaporator fan, begins timer sequence (55 ± 10-second de- lay). Induced-draft contactor closes and induced-draft motor starts.
Centrifugal switch closes. Pilot valve opens, allowing gas to ¯ow to ®rst-stage pilot. Spark ignitor ignites pilot ¯ame. Sensor detects ¯ame, energizes main gas valve coil and main gas valve opens. Gas ¯ows to main burners and ®rst-stage burners ignite. Spark ignitor shuts off and pilot remains on.
The spark ignitor will continue to spark for 90 seconds until pilot ¯ame is sensed. If the pilot fails to ignite or the sensor fails to detect ¯ame, the pilot valve closes and the spark ignitor shuts off for 300 seconds (5 minutes). During this time the induced draft motor remains on to purge any unburnt gas from the combustion tubes. This ignition se- quence will repeat inde®nitely.
When time-delay sequence is complete, time-delay relay closes and evaporator-fan motor starts.
When additional heat is needed on 034,044 units, W2 is energized and a second coil in the main gas valve is ener- gized. This brings on an additional stage of heat. When second- stage thermostat is satis®ed, the second-stage gas valve coil is deenergized.
When additional heat is needed on 054-074 units, W2 is energized, and pilot valve number 2 opens. Gas ¯ows to second- stage pilot, and spark ignitor ignites pilot ¯ame. Sensor de- tects ¯ame, energizes the main gas valve coil, and main gas valve number 2 opens. Gas ¯ows to main burners and second- stage burners ignite. Second-stage spark ignitor shuts off. When second-stage thermostat is satis®ed, the second-stage gas valve coil is deenergized.
