Imperial Home Page -> Repair -> Accessories -> Gas Heater -> Page 8
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37. NO HEAT
a. Clogged fuel nozzle. b. No fuel pressure, or low fuel pressure. c. Ignition failure. d. Insufficient combustion air.
Although these causes
of failure are listed in the order of probability, it is advisable to
check simple causes first to avoid unnecessary disassembly of heater.
Proceed with the check as follows:
e. With ignition switch
on and car engine NOT running, turn heater blower switch on. The fresh
air blower should start immediately. Failure of this blower indicates
a defect in blower switch, fuse, blower, or in associated wiring. The
burner blower motor and pump assembly should also start when switch is
turned on. Failure of this motor to start can be caused by a defective
blower switch. A defective coupling between motor and fuel pump will
cause loss of fuel pressure, even if motor is running. Check voltage
at red terminal of ignition unit with a test light or voltmeter and if
voltage is satisfactory, replace burner blower motor.
f. If both blowers run,
check the fuel control valve by removing the white lead from terminal
block on front of heater case. Touch this lead to terminal and listen
carefully for a click as valve opens and closes. (The temperature
control should be in HIGH HEAT position for this test). The click of
valve is rather faint, but can be heard when engine is not running. If
valve fails to click, shut off ignition, remove four screws from
heater cover and lift it out far enough to install a jumper wire
directly between white terminal inside case and white terminal of the
solenoid valve. Disconnect overheat switch wires from these terminals
but leave all other wires connected. Temporarily replace cover of
heater case and turn on ignition. Touch white lead to terminal on
front of case again and check for valve action. If valve fails to
click with overheat switch shorted out, check voltage at white lead
with a test light or meter. If lead is hot, and valve fails to click
with overheat switch shorted out, the fuel valve solenoid coil is
defective and must be replaced.
CAUTION
Do not permit the
white lead to touch ground while
making these tests.
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g. If the solenoid
valve is operating properly, it will be necessary to check the
ignition unit. TURN IGNITION SWITCH OFF. Separate two sections of
ignition cable at the connector. Insert a dual-electrode automotive
type plug in end of ignition unit section of ignition cable and ground
plug to engine block. This plug should be adjusted to a gap of .085
inches. Turn ignition and heater switches on and check the plug for a
hot spark; If there is no spark, the ignition unit is defective and
must be repaired.
h. If there is a spark
at plug, reconnect ignition cable and check fuel pressure with a
"T" fitting and gage at outlet of fuel pump while car engine
is running. The pressure should be 21 to 23 psi. If pressure is
satisfactory, and heater does not ignite, it can be assumed that
nozzle is clogged or spark plug shorted out and burner assembly be
removed from heater. Fuel pressure as high as 27 psi is usually an
indication of a clogged nozzle.
i. Remove front of
heater case and remove burner assembly from heat exchanger. Pull
ignition cable and fuel line out of case and reconnect them to burner
assembly. Leave solenoid wires disconnected. Ground this assembly to
body of car and turn the heater switch on. Check for a spark at the
spark plug electrodes.
CAUTION
Be sure burner is
properly grounded and avoid touching any part
of assembly during this test.
j. If hot spark appears
at electrodes of spark plug, nozzle is defective and must be replaced.
If spark is being shorted to ground or is completely absent, replace
spark plug. If plug is shorted out by an accumulation of carbon, the
nozzle is probably at fault and the spray pattern should be checked.
k. To examine the
spray pattern, connect the white lead that was removed from front of
case directly to insulated terminal of valve solenoid. Disconnect
ignition cable from spark plug. Connect black lead to ground terminal
in a similar way. At the ignition unit, disconnect both white wires
and clip them together, using tape to insulate the connection. These
wiring connections will energize the solenoid directly without going
through the overheat switch (provided thermostat is calling for heat).
After making connections, start engine and turn heater blower switch
on (tempera-
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This page last updated April 26, 2001. Send us your feedback, and come join the Imperial Mailing List - Online Car Club
