Carrier 48TC 17 Series Service And Maintenance Instructions page 49

Minimum heating entering air temperature
When operating on first stage heating, the minimum
temperature of air entering the dimpled heat exchanger is
50_F (10_C) continuous and 45_F (7_C) intermittent for
standard heat exchangers and 40_F (4_C) continuous and
35_F (2_C) intermittent
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. 60. Set the outdoor−air thermostat at 35_F
(2_C) for stainless steel heat exchangers or 45_F (4_C)
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 can be compromised when heating is
PROBLEM
Burners Will Not Ignite.
Inadequate Heating.
Poor Flame
Characteristics.
Burners Will Not Turn
Off.
for stainless steel heat
Table 17 – Heating Service Troubleshooting
CAUSE
Misaligned spark electrodes.
No gas at main burners.
Water in gas line.
No power to furnace.
No 24V power supply to control
circuit.
Miswired or loose connections.
Burned-out heat anticipator in
thermostat.
Broken thermostat wires.
Dirty air filter.
Gas input to unit too low.
Unit undersized for application.
Restricted airflow.
Blower speed too low.
Limit switch cycles main burners.
Too much outdoor air.
Incomplete combustion (lack of
combustion air) results in:
Aldehyde odors, CO, sooting
flame, or floating flame.
Unit is locked into Heating mode
for a one minute minimum.
initiated using low entering air temperatures with
insufficient heating temperature rise.
Thermostat
TH1
W1
TH2
W2
Fig. 60 − OATL Connections
Troubleshooting Heating System
Refer to Tables 17 and 18 for additional troubleshooting
topics.
REMEDY
Check flame ignition and sensor electrode positioning.
Adjust as needed.
Check gas line for air, purge as necessary. After purging
gas line of air, allow gas to dissipate for at least 5 minutes
before attempting to relight unit.
Check gas valve.
Drain water and install drip leg to trap water.
Check power supply, fuses, wiring, and circuit breaker.
Check transformer. Transformers with internal overcurrent
protection require a cool down period before resetting.
Check all wiring and wire nut connections.
Replace thermostat.
Run continuity check. Replace wires, if necessary.
Clean or replace filter as necessary.
Check gas pressure at manifold. Clock gas meter for input.
If too low, increase manifold pressure, or replace with
correct orifices.
Replace with proper unit or add additional unit.
Clean filter, replace filter, or remove any restrictions.
Use high speed tap, increase fan speed, or install optional
blower, as suitable for individual units.
Check rotation of blower, thermostat heat anticipator
settings, and temperature rise of unit. Adjust as needed.
Adjust minimum position.
Check economizer operation.
Check all screws around flue outlets and burner
compartment. Tighten as necessary.
Cracked heat exchanger.
Overfired unit — reduce input, change orifices, or adjust
gas line or manifold pressure.
Check vent for restriction. Clean as necessary.
Check orifice to burner alignment.
Wait until mandatory one-minute time period has elapsed
or reset power to unit.
49
LCTB
W1
OALT
W2
C08442