Carrier 48TC*D08 appendix Troubleshooting Heating System, Minimum Heating Entering Air Temperature

Minimum Heating Entering Air Temperature

When operating on first stage heating, the minimum temperature of air entering the dimpled heat exchanger is 50_F continuous and 45_F intermittent for standard heat exchangers and 40_F continuous and 35_F intermittent for stainless steel heat exchangers. To operate at lower mixed-air temperatures, a field-supplied outdoor-air thermostat must be used to initiate both stages of heat when the temperature is below the minimum required temperature to ensure full fire operation. Wire the outdoor-air thermostat OALT (part no. HH22AG106) in series with the second stage gas valve. See Fig. 40. Set the outdoor-air thermostat at 35_F for stainless steel heat exchangers or 45_F for standard heat exchangers. This temperature setting will bring on the second stage of heat whenever the ambient temperature is below the thermostat setpoint. Indoor comfort may be compromised when heating is initiated using low entering air temperatures with insufficient heating temperature rise.

Thermostat	LCTB
TH1	W1
W1
	OALT
TH2
W2	W2

C08442

Fig. 40 - OATL Connections

Troubleshooting Heating System

Refer to Table 13 and 14 for additional troubleshooting topics.

48TC

	Table 13 – Heating Service Analysis
PROBLEM	CAUSE	REMEDY
	Misaligned spark electrodes.	Check flame ignition and sensor electrode positioning.
		Adjust as needed.
		Check gas line for air, purge as necessary. After purging
	No gas at main burners.	gas line of air, allow gas to dissipate for at least 5 minutes
		before attempting to relight unit.
		Check gas valve.
Burners Will Not Ignite.	Water in gas line.	Drain water and install drip leg to trap water.
	No power to furnace.	Check power supply, fuses, wiring, and circuit breaker.
	No 24 v power supply to control	Check transformer. Transformers with internal overcurrent
	circuit.	protection require a cool down period before resetting.
	Miswired or loose connections.	Check all wiring and wire nut connections.
	Burned---out heat anticipator in	Replace thermostat.
	thermostat.
	Broken thermostat wires.	Run continuity check. Replace wires, if necessary.
	Dirty air filter.	Clean or replace filter as necessary.
	Gas input to unit too low.	Check gas pressure at manifold. Clock gas meter for input.
		If too low, increase manifold pressure, or replace with
		correct orifices.
	Unit undersized for application.	Replace with proper unit or add additional unit.
Inadequate Heating.	Restricted airflow.	Clean filter, replace filter, or remove any restrictions.
	Blower speed too low.	Use high speed tap, increase fan speed, or install optional
		blower, as suitable for individual units.
	Limit switch cycles main burners.	Check rotation of blower, thermostat heat anticipator
		settings, and temperature rise of unit. Adjust as needed.
	Too much outdoor air.	Adjust minimum position.
		Check economizer operation.
		Check all screws around flue outlets and burner
	Incomplete combustion (lack of	compartment. Tighten as necessary.
Poor Flame		Cracked heat exchanger.
	combustion air) results in:
		Overfired unit — reduce input, change orifices, or adjust
Characteristics.	Aldehyde odors, CO, sooting
		gas line or manifold pressure.
	flame, or floating flame.
		Check vent for restriction. Clean as necessary.
		Check orifice to burner alignment.
Burners Will Not Turn	Unit is locked into Heating mode	Wait until mandatory one---minute time period has elapsed
Off.	for a one minute minimum.	or reset power to unit.

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