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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.
Do not permit the white lead to touch ground while making these tests.
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.
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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