Test Choke Heater; Diagnostic Tests - Guardian 4700 Repair Manual

Section 7

DIAGNOSTIC TESTS

TEST 41 - TEST CHOKE HEATER
DISCUSSION:
The Choke Heater is a sensitive heating element
wrapped around a temperature sensitive Bi-Metal
strip. The Bi-Metal strip positions the Choke Plate
during startup. Once running, the Bi-Metal strip will
also allow the Choke Plate to fully open. Power for
the heater element is supplied from Wire No. 14 to
assist the Bi-Metal strip in opening the Choke Plate
after starting. Failure of the Choke Plate to open will
cause an excessively rich fuel-air mixture and engine
performance will suffer.
PROCEDURE:
1. Verify that the Choke Plate on the carburetor is mechanically
free to move and is not binding. If the engine runs rough, check
the operation of the Bi-Metal strip. Allow the engine to run for
five minutes, then inspect the choke position. The Bi-Metal strip
should have been heated by the Choke Heater and should
have expanded to allow the Choke Plate to open fully.
2. If the Choke Plate did not open in Step 1, check the Choke
Heater. Set the VOM to measure DC voltage. Disconnect
Connector 1 at the Choke Assembly. Connect the positive (+)
meter test lead to Wire No. 14 (Connector 1, Pin 3) going to the
control panel. Connect the negative (-) meter test lead to a
clean frame ground. Set the Start-Stop switch to "START."
Battery voltage should be measured.
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3. If battery voltage was not measured in Step 2, set the VOM to
measure resistance. Disconnect Connector 1 at the Choke
Assembly. Connect one meter test lead to Wire No. 14
(Connector 1, Pin 3) going to the control panel. Connect the
other meter test lead to the 4-tab terminal for Wire No. 14 in
the control panel. Continuity should be measured.
4. Set the VOM to measure resistance. Connect one meter test
lead to Wire No. 14 (Connector 1, Pin 3) going to the Choke
Heater. Connect the other meter test lead to the exposed steel
portion of the Choke Heater/Bi-Metal strip. Approximately 37
ohms (±20%) should be measured. (Current draw of the Choke
Heater at nominal voltage is approximately 340 milliamps or
0.340 amps). If continuity is present the Choke Heater has a
short to ground.
RESULTS:
1. If Choke Plate is binding in Step 1, repair or replace binding
Choke Plate. If Choke Heater tests good, go to Test 35.
2. If battery voltage was not measured in Step 2 and continuity
was measured in Step 3, go to Test 29.
3. If continuity was not measured in Step 3, repair or replace Wire
No. 14 between the 4-tab Terminal and Connector 1.
4. If the resistance value is incorrect in Step 4 or the Bi-Metal strip
does not function with voltage present, replace the Choke
Heater.