39
RP-HRPD-IOM (07-22) 132210-B
TROUBLESHOOTING
NOTE: If the furnace is equipped with electronic modulation option AG39, AG40, AG41, or AG42,
see
for additional troubleshooting guidelines.
Table 21. General Troubleshooting
Symptom
Probable Cause
Remedy
A . Venter
motor will
not start on
power-vented
unit
1 . No power to furnace
Turn ON power and check supply fuses or circuit breaker
2 . No 24V power to venter relay
Turn up thermostat and check control transformer output
Check for loose or improper wire connections
3 . Defective venter relay
Replace defective part
4 . Defective motor or capacitor
Replace defective part
B . Pilot will
not light
on power-
vented unit
with venter
operating
1 . Manual valve not open
Open manual valve
2 . Air in gas line
Bleed gas line
3 . Dirt in pilot orifice
Remove pilot orifice and clean with compressed air or solvent
4 . Gas pressure too high or too low
Adjust gas pressure (refer to
Measure and Adjust Manifold (Outlet) Gas
section)
5 . Kinked pilot tubing
Replace tubing
6 . Pilot valve does not open
If 24V power is available at valve, replace valve
7 . No spark
a . Loose wire connections
Ensure that all wires connections are solid
b . Transformer failure
Ensure that 24V power is available
c . Incorrect spark gap
Maintain spark gap at 7/64 inch
d . Spark cable shorted to ground
Replace worn or grounded spark cable
e . Spark electrode shorted to ground
Replace pilot if ceramic spark electrode is cracked or grounded
f . Drafts affecting pilot
Ensure that all panels are in place and are tightly secured to prevent drafts
at pilot
g . Ignition control not grounded
Ensure that ignition control is grounded to furnace chassis
h . Faulty ignition controller
If 24V power is available to ignition controller and all other causes have been
eliminated, replace ignition control
8 . Optional lockout device interrupting control
circuit due to above causes
Reset lockout by interrupting control at thermostat
9 . Faulty combustion air proving switch
Replace combustion air proving switch
C . Pilot lights
but main
valve will not
open
1 . Manual valve not open
Open manual valve
2 . Main valve not operating
a . Defective valve
If 24V power is available at valve connections and valve remains closed,
replace valve
b . Loose wire connections
Check and tighten all wiring connections
3 . Ignition control does not power main valve
a . Loose wire connections
Check and tighten all wiring connections
b . Flame sensor grounded, pilot lights, and
spark continues
Ensure that flame sensor lead is not grounded and that insulation or ceramic
is not cracked; replace as required
c . Incorrect gas pressure
Adjust gas pressure (refer to
Measure and Adjust Manifold (Outlet) Gas
section)
d . Cracked ceramic at sensor
Replace sensor
e . Faulty ignition controller
If all checks listed in
Spark Ignition System Maintenance
no other cause, replace ignition controller (do not attempt to repair ignition
controller, which has no field-replaceable parts)
f . Poor microamp signal
Adjust pilot regulator
D . Insufficient
heat with
heater
operating
1 . Dirty filters in blower system
Clean or replace filters
2 . Incorrect manifold pressure
Check manifold pressure (refer to
Measure and Adjust Manifold (Outlet)
section)
3 . Limit control cycling on
Check air throughput
4 . Improper thermostat location or adjustment Refer to thermostat manufacturer’s instructions
5 . Belt slipping on blower
Adjust belt tension
E . Cold air at
startup
1 . Fan control improperly wired
Ensure that wiring connections are in accordance with wiring diagram
2 . Defective fan control
Replace fan control
F . Cold
air during
operation
1 . Incorrect manifold pressure
Check manifold pressure (refer to
Measure and Adjust Manifold (Outlet)
section)
2 . Blower set for too low temperature rise
Decrease blower speed or increase static pressure
