Heater System Solving Guide
FAUL
T CODE THUMBNAILS –
PAGE
F 18
FAUL
T CODE THUMBNAILS –
PAGE
F 18
Heater System Solving Guide
Fault Code Thumbnails F
ault Conditions with NO CODE
F
AULT
C
ODE
T
HUMBNAILS
F
AULT
C
ONDITIONS
WITH
NO CODE
F
AULT
C
ONDITIONS
WITH
NO CODE
UHS, IDL2
P
ARTS
T
HAT
M
AY
B
E
N
EEDED
• Fuses (FC1, FC2, FC3, FC4)
• Transformer
• Fuse Board
• Control Module
• Wiring
• Wiring Harness
D
IAGNOSTIC
S
EQUENCE
Heater Will Not Power Up
A. Verify that low & high voltage is being output from fuse board:
Disconnect the P5 connector from fuse board plug, and measure for
24vac between pins on fuse board receptacle. Reconnect the P5 plug, and
disconnect P6 connector plug on the fuse board. Measure for 120VAC
between pin 3 and 6 of receptacle on fuse board.
If OK, reconnect P6 plug and proceed to next fault condition,
Low
Voltage Circuit Fault.
Otherwise, reconnect P6 plug and proceed to
step B
.
B. Verify heater is getting field power by measuring for field supply voltage
across terminals of TB1 terminal block on fuse board.
C. Inspect fuse board wiring, and ensure all plugs are securely fastened to
fuse board.
D. Remove FC1 and FC2 fuses from fuseholder. Measure continuity across
fuse.
If fuses are open, proceed to fault condition
Open Fuse: FC2 or F1
.
If fuses are OK, reinstall them and proceed to
step E
.
E. Check that the proper voltage selector plug is installed in fuse board.
F. Disconnect P4 connector from fuse board plug. Measure for 24VAC
between pins 1 & 2 of plug of transformer and for 120VAC between pins
4 & 6.
If 24VAC or 120VAC is not present, replace transformer.
Otherwise, replace fuse board.
Low Voltage Circuit Fault
G. Disconnect P5 connector from fuse board plug. Measure for 24VAC
across pins. Reconnect plug.
If OK, proceed to
step H
. Otherwise proceed to
step K
.
H. Inspect control module wiring. Ensure all plugs are securely fastened to
control module.
I. Verify 24VAC across R and C terminals on control module.
If not OK, replace harness.
J. Remove F1 fuse from fuseholder. Measure continuity across fuse.
If OK, replace control module.
If fuse is open, proceed to fault condition
Open Fuse: FC3 or F1
.
K. Remove FC3 fuse from fuseholder. Measure continuity across fuse.
If fuse is open, proceed to fault condition
Open Fuse: FC3 or F1
.
If OK, reinstall fuse and proceed to step L.
L. Disconnect P4 connector from fuse board plug. Measure for 24VAC
between pins 1 & 2 of plug from transformer. If 24VAC is not present,
replace the transformer. Otherwise, replace fuse board.
Open Fuse: FC2 or FC1
M. Check that proper voltage selector plug is installed.
N. If 120VAC plug is installed but field supply voltage is 240VAC, FC1 and
FC2 fuses will have opened. Install the correct voltage selector plug
(240VAC) and new FC1 and FC2 fuses.
O. Inspect transformer wiring. Ensure insulation on wiring is not worn.
If OK, replace the transformer.
Open Fuse: FC3 or FC1
P. Inspect gas valve wiring. Ensure insulation on wiring is not worn.
Q. Measure for resistance across gas valve terminals and between each ter-
minal and ground. If short exists, replace gas valve.
R. Inspect control module wiring. Ensure insulation on wiring is not worn.
If OK, replace the control module.
Open Fuse: FC4
S. Inspect ignitor wiring. Ensure insulation on wiring is not worn.
T. Inspect blower wiring. Ensure insulation on wiring is not worn.
U. Disconnect ignitor plug from control module. Measure resistance across
Igniter. If shorted, replace ignitor.
V. Disconnect blower plug from control module. Measure resistance across
blower windings. Winding resistance across lead should be in the following
range:
IDL2:
Black to White 10-14 ohms
Red to White 18-22 ohms
UHS:
Red to White 8-9 ohms
If measured values vary substantially from these values, blower is defective
and must be replaced. Otherwise, replace the control module.