Onan Demo

Click HERE to download and / or print this document in booklet form

GMC MOTORHOME
INTERNATIONAL CLUB

MANY THANKS TO LEN MORTIMER FOR THE COVER ART WORK & ALL THOSE GMC PACIFIC CRUISERS THAT REVIEWED THIS DOCUMENT PRIOR TO PUBLICATION.

THE CONTENTS OF THIS DOCUMENT ARE BASED UPON PERSONAL EXPERIENCE GAINED BY “HANDS-ON” VEHICLE MAINTENANCE OVER MANY YEARS. THEY ARE “ONE MAN’S” VIEWPOINT & DO NOT REPRESENT AUTHORIZED DATA PERTAINING TO THE GMC MOTORHOME. IT IS THE READER’S RESPONSIBILITY TO ESTABLISH HIS/HER POSITION ASSOCIATED WITH EACH SUBJECT MATTER BEFORE VEHICLE REPAIR &/or MODIFICATIONS ARE ACCOMPLISHED.

• AIR FILTER:
- K&N WASHABLE FILTER #R-1030 FOR 6 KW ONLY
-CUT OFF UPPER RUBBER ELBOW FOR FLAT SURFACE & MOUNT W/ORIGNAL BOLT

• OIL FILTER:
- MANY AFTERMARKET FILTERS AVAILABLE...SELECT ONE W/BUILT IN BYPASS

• STARTER MOTOR:
- ORIGINAL STARTER (191-1052) IS DISCONTUNED W/O REPLACEMENT
- ASK FOR 191-1949-03 STARTER…MAY REQUIRE SLIGHT MOD TO CLEAR BRACKET

• ONAN CARBURATOR IS DISCONTINUED W/O REPLACEMENT
- REBUILD SERVICE AVAILABLE AT:
LUIS SALES, WALBRO CORP. CARBURATOR DIV.
6242 GARFIELD ST
CASS CITY, MI 48726
517-872-2131
- REPLACEMENT CARB. REBUILD GASKET: BRIGGS & STRATTON P/N 281165S
- MAIN/RUN JET SEAL: 1/8” ID x 1/4” OD O’RING
- SET FLOAT LEVEL AT 1/16” (NOT 3/32” AS NOTED IN SOME GMC MANUALS)

• STARTER MOUNTING BRACKET
- REPLACE BROKEN BRACKET W/HIGH STRENGH STEEL BRACKET FROM
RAGUSA PATTERNS, SANTA ANA, CA 949-261-5898 P/N RV-04

• VERIFY HOUSE/ONAN BATTERY IS FULLY CHARGED, BATTERY CABLES CLEANED AT BOTH ENDS WITH ANTI-CORROSION APPLIED (NCP-2) ANTI-CORROSION COMPOUND TO BATTERY TERMINALS/ CONNECTORS & ANTI-OXIDANT (NOALOX) ANTI-JOINT COMPOUND APPLIED TO OTHER CABLE ENDS.

• OBSERVE THE STARTER RELAY K-1* (LARGE RELAY LOCATED JUST BELOW THE
CONTROL BOARD) AS FOLLOWS:
• THE SMALL RIGHT TERMINAL "I" SHOULD NOT HAVE ANY WIRES ATTACHED.
• IF IT DOES, REMOVE ALL WIRES & ATTACHED TO THE LARGE LEFT TERMINAL.

• OBSERVE THE AIR FILTER AS BEING CLEAN.......REPLACE WITH K&N's R-1030 FILTER

• PUSH & PULL ON THE STARTER TO VERIFY THAT THE STARTER IS ATTACHED FIRMLY W/O A BROKEN BRACKETT OR LOOSE BOLTS.

NOTE:
(*) K-1 Relay is not a common Automotive Starter relay since it has an internal connection of one lead of the coil to the large right terminal. Requires a Good Ground connection to the "S" for Relay action.

• KEEP WATER OFF OF ONAN KEEP WATER OFF OF ONAN
* IF IT GETS WET, DRY IT OUT BEFORE STARTING [24 HRS MIN.]

• CLEAN CONNECTORS & BOARD TERMINALS W/ ELECTRICAL CLEANER
* CRC INC. #2-26 ELECTRICAL GRADE CONTACT CLEANER OR EQUAL @ HOME DEPOT HOME CENTER [ELECTRICAL DEPT.]

• REPAIR J1 & J2 W/CLEANER & CAREFULLY CLOSE FEMALE SOCKETS [BACK TO ORIGINAL SHAPE] FOR BETTER CONTACT [HARDWIRE IF NECESSARY]

• VERIFY LOW OIL PRESSURE [LOP] CIRCUIT AS NOTED HEREIN [COULD SAVE AN ENGINE WHICH IS LOW IN OIL PRESSURE]

• BEFORE YOU DECLARE THE CONTROL BOARD FAULTY VERIFY:
    * FUSE F-1 [5 AMPS] IS FUNCTIONAL
    * J1 & J2 CONNECTOR IS FUNCTIONAL [CLEAN & REPAIR]
    * WIRE TERMINALS /BOARD TERMINALS ARE FUNCTIONAL
    * NO BROKEN OR SHORTED WIRES
    * LOP FUNCTIONAL [NOT SHORTED TO GROUND]
    * VOLTAGE REGULATOR [VR 1] IS DISABLED: TERM. 8 TO 11 @ 28 =/- 2 V AC

• HIGH SUSPECT IS FAILED BRIDGE RECTIFIER (BR):
REPLACE/ADAPT W/HIGHER VOLTAGE RATED BR (NTE 5328 OR EQUIVALENT)
NOT PIN COMPATIBLE & REQUIRES BASE MODIFICATION TO ALLOW INDIVIDUAL WIRE ATTACHEMENT
- SEE GMC MAINTENANCE MANUAL FOR BR TEST METHOD

• ONAN CIRCUIT BREAKER FAILURE:
REPLACE/ADAPT BUTTON TYPE W/MORE RELIABLE UNIT (GE/WESTINGHOUSE
“QUIK LAG” TYPE @ 40 OR 50 AMP.)
- PROBE EACH CB WIRE TERMINAL W/RESPECT TO CHASSIS GROUND TO DETERMINE IF AC IS PRESENT

• LOSS OF RESIDUAL MAGNETISUM:
DISASSEMBLY OR ELECTRICAL FAULT MAY CAUSE LOSS/REVERSAL OF RESIDUAL MAGNETISUM
- POLARIZE MAGNET BY A FLASH/MONENTARY CURRENT FLOW INTO FIELD WINDING:
- REMOVE BR & APPLY FLASH/MONENTARY BATTERY + VOLTAGE TO THE FIELD + WIRE & CHASSIS (-) VOLTAGE TO FIELD NEGATIVE (–) WIRE (MONENTARY ONLY)

NOTE: THE CONTROL BOARD IS FOR ENGINE OPERATION ONLY & HAS NOTHING
TO DO WITH AC POWER GENERATION

• PRESS CONTROL BOARD'S STOP SW: NON FUNCTIONAL/WILL NOT STOP
* REMOVE WIRES FROM BOARD'S UPPER TERMINALS 1, 2 & 3
- ATTACH JUMPER BETWEEN UPPER TERMINALS 1 & 2
- NON FUNCTIONAL/WILL NOT STOP
- SUSPECT FAULTY CONTROL BOARD
- FUNCTIONAL
- SUSPECT FAULTY REMOTE CONTROL PANEL OR ASSOCIATED WIRING
* TO FORCE STOP FUNCTION
- REMOVE WIRE FROM BOARD TERMINAL 11, 9 OR 1

NOTE: RECONNECT WIRES & PROBE BOARD TERMINAL 9 TO 1 ..... THERE SHOULD BE LESS THAN 1 VOLT DC PRESENT WITH ONAN NOT RUNNING. IF VOLTAGE IS PRESENT, REMOVE WIRE FROM BOARD TERMINAL 9 & PROBE TERMINAL 9 & THEN WIRE ONLY FROM TERMINAL 9 TO SEE IF VOLTAGE IS PRESENT FROM THE BOARD OR THE ONAN WIRING.

• IF ANY OF THE RC PANEL FUNCTIONS ARE NON RESPONSIVE
- SUSPECT THE 4 WIRE CONNECTOR FAULTY (LOCATED IN ONAN COMPARTMENT NEAR REAR ON COMPARTMENT FLOOR)
- ELIMINATE THE 4 WIRE CONNECTOR BY HARD WIRE BYPASS

• PRESS RC PANEL START SW & STOP SW: ONAN SHOULD RESPOND
- IF NON FUNCTIONAL
- REMOVE WIRES FROM UPPER BOARD TERMINALS 1, 2 & 3
* JUMPER UPPER TERMINAL 1 TO 3: ONAN SHOULD START
- IF FUNCTIONAL
- SUSPECT RC PANEL/WIRING FAULTY
- IF NON FUNCTIONAL
- SUSPECT CONTROL BOARD FAULTY
* JUMPER UPPER TERMINALS 1 TO 2 (ONAN RUNNING): ONAN SHOULD STOP
- IF FUNCTIONAL
- SUSPECT RC PANEL/WIRING FAULTY
- IF NON FUNCTIONAL
- SUSPECT CONTROL BOARD FAULTY

• PRESS CONTROL BOARD START SW & NO STARTER ACTION
• JUMPER K-1 STARTER RELAY “S” TERMINAL (SMALL) TO CHASSIS GROUND
* STARTER ACTION
- CONTROL BOARD OR WIRING FAULTY
* NO STARTER ACTION
- APPLY +12V DC TO K-1 STARTER RELAY “S1” TERMINAL (LARGE, LEFT SIDE)
- STARTER ACTION
- K-1 RELAY FAULTY
- NO STARTER ACTION
- APPLY +12V DC TO STARTER SOLENOID “S” TERMINAL (SLIP-ON TERM.)
- STARTER ACTION
- WIRING BETWEEN K-1 & STARTER SOLENOID FAULTY
- NO STARTER ACTION
- STARTER FAULTY

NOTE:
IF STARTER EVER STAYS ENGAGED AFTER ONAN STARTS
- PULL SLIP-ON TERMINAL WIRE FROM STARTER SOLENOID TO STOP STARTER
- IF STARTER WILL NOT STOP: SUSPECT STARTER SOLENOID (CLEAN & LUBE)
NOTE: REMOVE BATTERY CABLE TO STOP - IF STARTER STOPS: SUSPECT K-1 RELAY & ASSOCIATED DRIVE CIRCUIT

2) Measure DC Voltage between Terminals 5 & 1 (s/b ~ 12.8 v dc) _______________v dc

3) Measure DC Voltage between Terminals 8 & 1 (s/b ~ 12.8 v dc) _______________v dc

4) W/Starter engaged, measure dc voltage Term. 10 & 1 (s/b 10.5 v dc min.) _______________v dc

5) Jumper Terminals 9 to 5, Hear Fuel Pump & Start Onan FUEL PUMP RUN YES_____ NO____
NOTE: If No Start: Ignition, Fuel supply or wiring problem START YES_____ NO____

6a) W/Onan Running, Measure AC Voltage between Term. 8 & 11 (s/b 26 to 31 v AC) ___________v ac
6b) Measure DC Voltage between Term. 12 & 11 (s/b near zero) ___________ v dc
6c) Measure DC Voltage between Upper Term. 1 &2 (s/b ~ 12 v dc) _ __________v dc
6d) Remove the jumper.....does the Onan continue to run * * * * RUN Yes____ No____

7a) Stop Onan & measure DC Voltage between Term. 12 & 11 ( s/b ~ 12.8 v dc) __________v dc
7b) Pull wire from Term. 12.........................Try to Start START YES____ NO___*

8a) Stop Onan & measure DC Voltage between Upper Term. 1 & 2 (s/b ~ zero v dc) _________v dc
8b) Pull wire from UPPER Term. 1 , 2 & 3........Try to Start START YES____ NO___*

NOTE: 1) *If STEPS 1 THRU 6 (except 6d) is OK & Step 7 & 8 is No Start: Suspect Control Board !!!
2) "S/B~" Means "Should Be Approximate value"