Filter
Top Products
40
Table 31 — Heating Service Analysis
Table 32 — Durablade Economizer Service Analysis
LEGEND
PROBLEM CAUSE REMEDY
Burners will not
ignite.
Misaligned spark electrodes. Check flame ignition and sensor electrode positioning. Adjust as
needed.
No gas at main burners. 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.
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 circuit. Check transformer. Transformers with internal overcurrent protection
require a cool-down period before resetting. Check 24-v circuit
breaker; reset if necessary.
Miswired or loose connections. Check all wiring and wirenut connections.
Burned-out heat anticipator in thermostat. Replace thermostat.
Broken thermostat wires. Run continuity check. Replace wires, if necessary.
Inadequate heating.
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.
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, Adjust pulley.
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.
Poor flame
characteristics.
Incomplete combustion (lack of
combustion air) results in:
Aldehyde odors, CO (carbon monoxide),
sooting flame, or floating flame.
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.
Burners will not
turn off.
Unit is locked into Heating mode for a
one minute minimum.
Wait until mandatory one minute time period has elapsed or reset
power to unit.
PROBLEM CAUSE REMEDY
Damper does not
open.
Evaporator fan not on. Check wiring between G on connection board and evaporator-fan
contactor.
No power to economizer motor. 1. Check that SW3 is making proper contact with the damper blade.
2. Check continually across R1 coil. If not connect, replace relay R1.
3. Check diode D18. If diode is not functioning properly, replace D18.
4. Check wiring in economizer relay pack. (See unit label diagram.)
Economizer motor failure. If there is 24 vac power at the motor terminals, but motor is not operat-
ing, replace motor.
Economizer
operation limited to
minimum position.
OAT or EC set too high. 1. Set at correct temperature (3 F below indoor space temperature).
2. Check OAT or EC by setting set point above outdoor temperature or
humidity level. If switch does not close, replace OAT or EC.
Check wiring of economizer relay packs. 1. Check continuity across relay R2 coil. If not connected, replace R2
relay.
2. Check continuity across relay R3 coil. If not connected, replace R3
relay.
Check SAT. If supply-air temperature is over 57 F, switch T2 should be closed. If
not, replace SAT.
Damper does not
close.
Incorrect wiring or wiring defects. 1. Check switches 2 and 4. If non-operational, replace.
2. Check diode D19. If diode D19 is not functioning properly, replace.
3. Check wiring on economizer and on economizer relay pack. (See
unit label diagram.)
Check SAT. If supply-air thermostat is below 52 F, switch T1 should be closed. If
not, replace SAT.
Economizer motor failure. If there is 24 vac power at motor terminals, but motor is not operating,
replace the motor.
EC —
Enthalpy Control
OAT —
Outdoor-Air Thermostat
SAT —
Supply-Air Thermostat
SW —
Switch