Carrier 48AY020-060, 48EW, 48EY024-068, 48AW, 48EK, 48AK, 48AJ, 48EJ Heat Interlock Relay Wiring

GAS HEATING, VARIABLE AIR VOLUME (VAV) UNITS — All of the gas heating control is performed through the integrated gas control (IGC) board. The control module board serves only to initiate and terminate heating operation.

NOTE: The unit is factory-configured for disabled occupied heating. DIP switch 5 is used to enable occupied heating (DIP switch 5 set to OPEN).

Variable Air Volume (VAV) occupied heat is controlled by return-air temperature (RAT) using a 5k thermistor located just below the outdoor-air dampers. A VAV unit without a space temperature sensor is also controlled by RAT. A VAV unit with a space temperature sensor has Unoccupied Heat controlled by space temperature (SPT).

The control module board is powered by 24 vac. When there is a call for heating (either Morning Warm-Up, Unoccu- pied, or Occupied modes), power is sent from the control mod- ule board to W on each of the IGC boards and W2 of the main gas valve. When heating, the control module board will ener- gize a field-supplied heat interlock relay output to drive the VAV terminal boxes wide open. The HIR is not required on a DAV system. See Fig. 59. In the Occupied mode the indoor-fan motor will be operating and the outdoor-air dampers will be in the minimum position. In the Unoccupied mode the indoor-fan motor will be off, but will energize 45 seconds after the call for heat and the outdoor-air dampers will move to the IAQ Unoccupied position (generally set to zero in the Unoccupied mode). The duct pressure sensor will signal to the variable fre- quency drive to operate at full speed since all terminals have been driven open. An LED on the IGC board will be on during normal operation. A check is made to ensure that the rollout switches and limit switches are closed and the induced-draft motors are not running. The induced-draft motors are then en- ergized 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.

When ignition occurs the IGC board will continue to moni- tor the condition of the rollout and limit switches, the hall effect sensor, and the flame sensor.

If the call for heat lasted less than 1 minute, the heating cy- cle will not terminate until 1 minute after heat became active. When heating is satisfied, the power will be interrupted to the IGC board and W1 and W2 of the main gas valve. If the unit is controlled through a room sensor, the indoor fan will be operat- ing in the Occupied mode and turned off after 45 seconds in the Unoccupied mode.

STAGED GAS UNIT HEATING — The Staged Gas Control option offered on 48EJ,EK,EW,EY024-068 and 48AJ,AK,AW, AY020-060 units adds the capability to control the rooftop unit’s gas heating system to a specified Supply Air Tempera- ture Set Point for purposes of tempering a cool mixed-air con- dition. The gas heating system employs multiple heating sec- tions. Each section is equipped with a two-stage gas valve. The gas valves are sequenced by a factory-installed staged gas con- troller (SGC) as required to maintain the user-specified Supply Air Set Point. Up to eleven stages of heating control are avail- able, based on quantity and heating capacity sizes of the indi- vidual heat exchanger sections provided in the base unit. In addition to providing system control for tempering heat opera- tion, the new SGC also controls Demand Heat sequences for both First-Stage (W1) and Second-Stage (W2 or full-fire) operation.

Tempering of supply air is desirable when rooftop units are operating in ventilation mode (economizer only operation) at low outdoor temperatures. At low outdoor temperatures, the mixed air temperature (combination of return-from-space tem- perature and outdoor/ventilation air temperature) may become too low for the comfort of the occupants or for the terminal reheat systems. The tempering function adds incremental steps of heat capacity to raise the temperature of the mixed air up to levels suitable for direct admission into the occupied space or to levels consistent with reheat capabilities of the space termi- nals. Refer to Table 37 for the staged gas heating control sys- tem components. Refer to Table 38 for the heating system con- troller (SGC) inputs. The heating system controller (SGC) out- puts consist of six relays (K1 through K6) which control the individual gas valves.

	TRAN2
B	COM
CB4	SECONDARY
3.2 AMPS	24 VOLT

BASE MODULE

CONTROL BOARD

INDOOR FAN RELAY COM

T

30

T29

T

28

LEGEND

CB — Circuit Breaker

COM — Common

HIR — Heat Interlock Relay

T — Terminal

TRAN — Transformer

HIR

FIELD

INSTALLED

(HN61KK040)

(24V, 9.5VA)

Fig. 59 — Heat Interlock Relay Wiring

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