GMC 1976 ZEO 6083 Maintenance Manual page 767

FURNACE TROUBLE DIAGNOSIS
BURNER WILL NOT LIGHT
FURNACE
24G- 5
IMPORTANT NOTE : Before any diagnosis is attempted on the furnace, there are two necessary and sufficient
external conditions that must be met.
1 . With the thermostat calling for heat, there must be 12 volts (absolute minimum of 10.5
volts) present at the furnace.
2. With the thermostat calling for heat, there must be a gas pressure of 11" of water
present to the furnace measured at the range/oven.
o. Check to Make
Results Go To Problem
1 . a. Turn off gas.
b . Make sure ignition wire is secure
Spark Present
#2
on the spark electrode .
c. Remove locking nut from the spark
electrode.
d . Turn on thermostat .
No Spark #3
e . Hold spark electrode approx . 1 / z"
from the burner and check for
sparking .
2. a. Replace the spark electrode. (Turn
Gas Present Primary air adjustment too
the locking nut on finger tight .) lean .
b. Turn on L.P.G .
c. Turn on the thermostat .
d. Sniff for L.P. fumes at the right
No Gas Present
#7
hand exterior furnace vent.
3 .
a. Check to make sure the ignition
Ground wire not connected. Loose ground to the ignition
pak ground is connected to ground
pak .
at the burner housing and at the
ignition pack .
Ground wire securely
#4
connected .
4. a. Check for correct polarity at the
Polarity not correct.
Polarity wrong, switch wires,
ignition pak ground (black wire) on
right; hot (red wire) on left .
Polarity is correct. #5
5. a. Check the voltage at the hot wire
12 volts .
Defective ignition pak.
red wire) at the ignition pak with
the thermostat on.
0 volts .
#6