Duty Cycle Valve, Control Unit

Duty cycle valve, checking

- operate switch on remote control US 4480/3
^ duty cycle valve must audibly click

If duty cycle valve clicks, continue with test (B) (checking control unit)

If duty cycle valve does not click, perform the following test



- remove connector from duty cycle valve -check prongs of the connector and of the duty cycle valve for correct positioning (must not be damaged or pushed in)
- measure voltage supply with multimeter US 1 1 19 Note

Preset multimeter to the 20VDC range prior to making test connection.

- operate remote control US 4480/3
^ specification - approx. battery voltage

If NO:
- check for open circuit to duty cycle valve, power supply relay, and control unit, using current flow diagram
- make corrections if necessary

If NO open circuits
- replace power supply relay

If voltage spec. is not obtained
- replace control unit

- measure duty cycle valve resistance
^ specification - 2-3 ohms

If NO
- replace duty cycle valve
Control unit, checking

Cold running enrichment mode



- remove wires from thermoswitch (A) and bridge them (B)
- operate remote control US 4480/3
^ duty cycle constant 80 +/- 2%

If NO:
- check for breaks in wiring using current flow diagram
- make corrections if necessary

If NO breaks in wiring:
- replace control unit
- repeat test
Stand-by mode
- remove bridge (B)
- operate remote control US 4480/3
^ duty cycle constant 50 +/- 2%

If NO
- check for breaks in wiring using current flow diagram
- make corrections as necessary

If NO breaks in wiring:
- replace control unit
- check thermoswitch (page 4)
- repeat test
Oxygen sensor regulating function of control unit

- remove wires from thermoswitch



- pull apart connector for oxygen sensor cable and hold connector (1) of the green cable on ground (A)
- operate remote control US 4480/3
^ duty cycle must exceed 87%

If NO:
- check for breaks in wiring using current flow diagram
- make corrections if necessary

If NO breaks in wiring: control unit is defective
- replace control unit
- connect a 1.5 volt (flashlight type) battery as follows:
^ (+) terminal to oxygen sensor green wire, (-) to ground

- operate remote control US 4480/3
^ duty cycle must fall below 20%

If NO: control unit is defective
- replace control unit
- repeat test