SUPPLY AIR TEMPERATURE RESET — Supply air tem- perature reset is used to reset the supply-air temperature utility. A 4 to 20 mA signal (field-supplied) is required. The reset op- tion does not require enabling.
POWER EXHAUST OPERATION — Power exhaust has two options (constant volume and modulating) that have the following sequence of operation:
The constant volume power exhaust stage 1 (CVPE1) is en- abled when the indoor fan has been energized and the desired outdoor-air damper position for the economizer increases above the first constant volume (CV) power exhaust stage 1 point (PES1). The PES1 factory default value is set at 25%. The constant volume power exhaust stage 2 (CVPE2) is en- abled when the desired outdoor-air damper position for the economizer increases above the second CV power exhaust stage 2 point (PES2). The PES2 factory default value is set at 75%. Each stage is disabled when the desired damper position decreases below the respective set points.
The modulating power exhaust is enabled when the indoor fan is energized and the building pressure has exceeded the in- dividual sequencer set points. The default set points are 0.04 in. wg (6.3 vdc) for stage 1, 0.10 in wg (6.8 vdc) for stage 2,
0.16in wg (7.3 vdc) for stage 3, and 0.23 in. wg (7.8 vdc) for stage 4, 0.29 in. wg (8.3 vdc) for stage 5, and 0.35 in. wg (8.8 vdc) for stage 6 power exhaust sequencer. Each stage also requires that the building pressure is reduced until it drops be- low the disable set point. The default set points are 0 in wg. (6.0 vdc) for stage 1, 0.060 in. wg (6.5 vdc) for stage 2, 0.13 in. wg (7.0 vdc) for stage 3, 0.19 in. wg (7.4 vdc) for stage 4,
0.25in. wg (8.0 vdc) for stage 5, and 0.31 in. wg (8.5 vdc) for stage 6 power exhaust sequencer. Both of these set points are changed at the specific controlling sequencer. It is not forcible from CCN.
If the indoor fan is on, then PEXE = ON. If the indoor fan is off, then PEXE = OFF. In addition, on units equipped with the Expansion I/O module, the control module board may have di- rect access 4 to 6 Modulated Power Exhausted stages bypass- ing an external sequencer device. These stages will be con- trolled directly in fire/smoke modes.
SMOKE CONTROL MODES — The 48AJ,AK,AW,AY and 48EJ,EK,EW,EY units with an optional expansion board per- form fire and smoke control modes. The expansion board pro- vides 4 modes which can be used to control smoke within the conditioned area. The modes of operation are fire shutdown, pressurization, evacuation, and smoke purge. See Table 41.
SMOKE DETECTOR — A smoke detector can be used to initiate fire shutdown. This can be accomplished by a set of normally closed pilot relay contacts which will interrupt power from the 24-v transformer, secondary ‘‘B’’ terminal to the con- trol circuit breaker (CB4). See Fig. 62. The wire that connects these two points is white and labeled ‘‘W78.’’
NOTE: On standard gas models, the indoor fan will continue to run 45 seconds after the call for heat has been terminated. If fire shutdown is initiated the fan will stop immediately. No 45-second delay will occur.
The smoke detector may be mounted in the return air duct or the supply duct. Carrier does not make recommendations as to specific smoke detector location due to liability considerations.
INDOOR AIR QUALITY (IAQ) CONTROL — The acces- sory IAQ sensor is required for IAQ control on the base control board. The Carrier sensors operate with a 4 to 20 mA signal. The 4 to 20 mA signal is connect to T13 (+) and T14 (-) on the base control board for the IAQ sensor, and T15 (+) and T16 (-) on the base control board for the OAQ (Outdoor Air Quality) sensor. The sensor is field-mounted and wired to the base con- trol board installed in the unit main control box. The IAQ sen- sor must be powered by a field-supplied 24-V power supply (ungrounded). Do not use the unit 24-V power supply to power sensor.
Fig. 62 — Field-Supplied Smoke Detector Wiring
NOTE: The Carrier IAQ/OAQ sensors are shipped configured for a 0 to 10 Vdc signal for use on previously designed PIC (Product Integrated Control) products. This signal must be changed to the 4 to 20 mA signal to be used on these products, which is accomplished through a jumper change. The IAQ/ OAQ input signals are also polarized, with (+) connecting to the odd numbered terminals and (-) connected to the even numbered terminals. Refer to Indoor-Air Quality Section in the Controls, Operation, and Troubleshooting Manual for further sequence of operation.
NOTE: The IAQ Control function was incorporated onto the base control board on these units with serial number of 0600F and later.
Once installed, the sensor must be enabled. The sensor is configured with default values which may be changed through network access software. To work properly, the IAQ sensor high and low reference points for the sensor that is used must match the configured values. The base control board reacts to a 4 to 20 mA signal from the IAQ sensor. The low reference (4 mA output) must be configured to the minimum IAQ sensor reading. The high reference (20 mA output) must be config- ured to the maximum IAQ sensor reading.
The IAQ sensor can be configured to either low or high priority. The priority value can be changed by the user. The default is low.
Low priority — When the priority is set to low, the initial con- trol is to the IAQ set point, but the outside air damper position will change to its minimum position when the following condi- tions occur:
•CV units with sensor — when the space temperature is greater than the occupied cooling set point plus 2° F or when the space temperature is less than the occupied heating set point minus 2° F.
•VAV units and CV units with thermostat — when the supply-air temperature is less than the supply-air temper- ature set point minus 8° F or when the supply-air temper- ature is greater than the supply air temperature set point plus 5° F for 4 minutes.
•When the outdoor air quality is greater than the outdoor air quality set point (ppm)
High priority — When the priority is set to high, the IAQ set point controls the outside air damper exclusively, with no re- gard to comfort conditioning.
TIME GUARD® CIRCUIT — The Time Guard function (built into the rooftop control module board) maintains a mini- mum off time of 5 minutes, a minimum on time of 10 seconds, and a 10-second delay between compressor starts.
CRANKCASE HEATER — Unit main power supply must remain on to provide crankcase heater operation. The crank- case heater in each compressor keeps oil free of refrigerant while compressor is off.
