Specifications

A redLEDisprovidedtoindicatethefunctionoftheboard.
Seethetablebelow.
LED STATUS FUNCTION
On Continuously Relay contact closed (normal operation).
Relay contact open (phase loss or phase
Blinking reversal has occurred) -- No power will be
supplied to the control system.
Off 24 vac control power not present (off).
Thermistor Troubleshooting -- The electronic con-
trol uses thermistors to sense temperatures used to control
operation of the unit. Resistances at various telnperatures are
listed in Tables 50 and 51. Thermistor pin connection points are
shown in the Major System Components section. The general
locations of the thermistors are shown the Major System
Components section.
AIR TEMPERATURES Air temperatures are measured
with 10 kilo-ohin thermistors. This includes supply-air temper-
ature (SAT), outdoor-air temperature (OAT), space telnperature
sensors (T55, T56, T58), and return air telnperature (RAT).
The supply air temperature (SAT) and outdoor air tempera-
ture (OAT) thermistors use a snap-mount to attach through the
unit sheet metal panels. The snap-mount tabs must be flattened
on the tip end of the sensor to release _br relnovat from the
panel. See Fig. 13. To reinstall, make sure the snap-mount tabs
extend out.
REFRIGERANT TEMPERATURES Condenser coil tem-
peratures are measured with 5 kilo-ohin thermistors. These
measurelnents provide an approximate saturated condensing
telnperature tbr each circuit (SCT.A, SCT.B). Ensure that ther-
mistors are placed at the correct location and axe snapped se-
curely over the return bend so that contact is made between the
thermistor and the tube.
THERMISTOR/TEMPERATURE SENSOR CHECK A
high quality digital volt-ohinmeter is required to perform this
check.
1. Connect the digital voltmeter across the appropriate ther-
mistor terminals at the J8 terminal strip on the Main Base
Board (see Major System Components section).
2. Using the voltage reading obtained, read the sensor tem-
perature fiom Tables 50 and 51.
3. To check thermistor accuracy, measure temperature at
probe location with an accurate thennocouple-type
temperature-measuring instrument. Insulate thennocou-
pie to avoid ambient temperatures tioln inlluencing
reading. Temperature measured by thennocouple and
telnperature determined fiom thermistor voltage reading
should be close, within 5° F if care was taken in applying
thennocouple and taking readings.
Table 47 -- Gas Heating Service Analysis
PROBLEM CAUSE REMEDY
Burners Will Not Ignite. Active alarm. Check active alarms using ComfortLink TM Scrolling Marquee.
No power to unit. Check power supply, fuses, wiring, and circuit breakers.
No power to IGC (Integrated Gas Control). Check fuses and plugs.
Heaters off due to time guard to prevent short cycling. Check using ComfortLink Scrolling Marquee.
Thermostat or occupancy schedule set point not Check using ComfortLink Scrolling Marquee.
calling for Cooling.
No gas at main burners. Check gas line for air and purge as necessary. After purging gas
line of air, allow gas to dissipate for at least 5 minutes before
attempting to re-light unit.
Water in gas line. Drain water and install drip.
Inadequate Heating. Dirty air filters. Replace air filters.
Gas input too low. Check gas pressure at manifold. Refer to gas valve adjustment on
page 90.
Thermostat or occupancy schedule set point only Allow time for W2 to energize.
calling for Wl.
Unit undersized for load.
Restricted airflow.
Too much outdoor air.
Limit switch cycles main burners.
Poor Flame
Characteristics.
incomplete combustion (lack of combustion air)
results in: Aldehyde odors, CO, sooting flame, or
floating flame.
Burners Will Not Turn Off. Unit is in Minimum on-time.
Unit running in Service Test mode.
Main gas valve stuck.
Decrease load or increase of size of unit.
Remove restriction.
Check economizer position and configuration. Adjust minimum
_osition using ComfortLink Scrolling Marquee.
Check rotation of blower, thermostat heat anticipator settings, and
temperature rise of unit. Adjust as needed.
Check al! screws around flue outlets and burner compartment.
Tighten as necessary.
Cracked heat exchanger, replace.
Unit is over-fired, reduce input. Adjust gas line or manifold
_ressure.
Check vent for restriction. Clean as necessary.
Check orifice to burner alignment.
Check using ComfortLink Scrolling Marquee.
Check using ComfortLink Scrolling Marquee.
Turn off gas supply and unit power. Replace gas valve.
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