GAS Heating System, Control Circuit | Carrier 48TC*D08 manual

Condenser Fan Motor Protection

The condenser fan motor is internally protected against overtemperature.

Control Circuit, 24-V

The control circuit is protected against overcurrent conditions by a circuit breaker mounted on control transformer TRAN. Reset is manual.

GAS HEATING SYSTEM

General

The heat exchanger system consists of a gas valve feeding multiple inshot burners off a manifold. The burners fire into matching primary tubes. The primary tubes discharge into combustion plenum where gas flow converges into secondary tubes. The secondary tubes exit into the induced draft fan wheel inlet. The induced fan wheel discharges into a flue passage and flue gases exit out a flue hood on the side of the unit. The induced draft fan motor includes a Hall Effect sensor circuit that confirms adequate wheel speed via the Integrated Gas Control (IGC) board. Safety switches include a Rollout Switch (at the top of the burner compartment) and a limit switch (mounted through the fan deck, over the tubes). (See Fig. 29 and 30.)

	INDUCED-
	DRAFT
	MOTOR	ROLLOUT
	MOUNTING	ROLLOUT
	MOUNTING	SWITCH
	PLATE	SWITCH
	PLATE
	BURNER	FLUE
	SECTION	EXHAUST
	INDUCED-	VESTIBULE
	DRAFT MOTOR	PLATE
	MANIFOLD
	PRESSURE
	TAP
	GAS	BLOWER
	VALVE	HOUSING
		C09153

Fig. 29 - Burner Section Details

Limit Switch

and Shield

C08284

Fig. 30 - Limit Switch Location

Fuel Types and Pressures

Natural Gas — The 48TC unit is factory-equipped for use with Natural Gas fuel at elevation under 2000 ft (610 m). See section Orifice Replacement for information in modifying this unit for installation at elevations above 2000 ft (610 m).

Gas line pressure entering the unit’s main gas valve must be within specified ranges. Adjust unit gas regulator valve as required or consult local gas utility.

Table 5 – Natural Gas Supply Line Pressure Ranges

UNIT MODEL	UNIT SIZE	MIN	MAX

48TC	All	4.0 in. wg	13.0 in. wg
48TC	All	(996 Pa)	(3240 Pa)
		(996 Pa)	(3240 Pa)

Manifold pressure is factory-adjusted for NG fuel use. Adjust as required to obtain best flame characteristic.

Table 6 – Natural Gas Manifold Pressure Ranges

UNIT	UNIT	HIGH	LOW	RANGE
MODEL	SIZE	FIRE	FIRE	RANGE
MODEL	SIZE	FIRE	FIRE

48TC	All	3.5 in. wg	1.7 in. wg	2.0--- 5.0 in. wg (Hi)
48TC	All	(872 Pa)	(423 Pa)	(498--- 1245 Pa)
		(872 Pa)	(423 Pa)	(498--- 1245 Pa)

Liquid Propane — Accessory packages are available for field-installation that will convert the 48TC unit to operate with Liquid Propane (LP) fuels. These kits include new orifice spuds, new springs for gas valves and a supply line low pressure switch. See section on Orifice Replacement for details on orifice size selections.

Fuel line pressure entering unit gas valve must remain within specified range.

Table 7 – Liquid Propane Supply Line Pressure Ranges

UNIT MODEL	UNIT SIZE	MIN	MAX
48TC	All	11.0 in. wg	13.0 in. wg
48TC	All	(2740 Pa)	(3240 Pa)
		(2740 Pa)	(3240 Pa)

Manifold pressure for LP fuel use must be adjusted to specified range. Follow instructions in the accessory kit to make initial readjustment.

Table 8 – Liquid Propane Manifold Pressure Ranges

UNIT MODEL	UNIT SIZE	HIGH FIRE	LOW FIRE
48TC	All	10.0 in. wg	5.0 in. wg
48TC	All	(2490 Pa)	(1245 Pa)
		(2490 Pa)	(1245 Pa)

Supply Pressure Switch — The LP conversion kit includes a supply low pressure switch. The switch contacts (from terminal C to terminal NO) will open the gas valve power whenever the supply line pressure drops below the setpoint. (See Fig. 31 and 32.) If the low pressure remains open for 15 minutes during a call for heat, the IGC circuit will initiate a Ignition Fault (5 flashes) lockout. Reset of the low pressure switch is automatic on rise in supply line pressure. Reset of the IGC requires a recycle of unit power after the low pressure switch has closed.