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Old 08-23-2016, 03:31 PM   #1
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Dometic woes

Fridge works on LP, refuses to fire up on AC. I'd like to have it fully functional. I did the onboard diagnosis and all tests passed, even the #2 test that sends 110v to the AC heating element. Ohm'd the element and it comes in at 38 ohms, pretty close to the 44ohm spec.
Any idea where to look next? I'm trying to avoid blindly throwing new motherboards and elements at it if I can.

Thanks
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Old 08-23-2016, 03:40 PM   #2
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I have a Norcold with an Amish cooling unit. My electric heater elements are very accessible. If yours are accessble, can you use an insulation piercing probe on a voltmeter to read the voltage going into the heating elements. If it has voltage going in, bad element. If no voltage going in, start checking backwards on the wire and circuit boards to see where it stops.
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Old 08-24-2016, 05:13 AM   #3
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That's the thing; I'm getting 120v at the J7 and J8 pins during the test, and the element is giving me 38 ohms resistance, suggesting both the board and element are good.
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Old 08-24-2016, 05:47 AM   #4
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What model Dometic?? I also assume you have the service manual for it.

Assuming its a 2652 (or similar) If you get 110 between J7 and J8, the heating element should be hot.

If you have shore power, with the frig in AUTO and the gas turned off, you should have 110 volts between J7 and J8.

The heating element may be bad, you could disconnect it from J7 and J8 and try wiring it directly to a 110 volt plug and plug it into a wall outlet to see if it gets hot.

You could also wire a 110 volt 60 watt light bulb to J7 and J8 and see if the light comes on.
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Old 08-24-2016, 08:52 AM   #5
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Hey Waiter. Its an RM3662. I can rule out the element, gets hot when plugged int wall outlet. I did your neat lightbulb trick. I'm definately getting 110 (124 actually) at J7/J8 during the self-test, but NOT when I just go and turn fridge on normally outside of the self-test mode
(shore or generator).


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What model Dometic?? I also assume you have the service manual for it.

Assuming its a 2652 (or similar) If you get 110 between J7 and J8, the heating element should be hot.

If you have shore power, with the frig in AUTO and the gas turned off, you should have 110 volts between J7 and J8.

The heating element may be bad, you could disconnect it from J7 and J8 and try wiring it directly to a 110 volt plug and plug it into a wall outlet to see if it gets hot.

You could also wire a 110 volt 60 watt light bulb to J7 and J8 and see if the light comes on.
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Old 08-24-2016, 10:25 AM   #6
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In the AUTO mode, the frig will automatically select a power source, AC or LP AND, if in the AC mode, the temperature is controlled by the electronics via a thermisiter.

HOWEVER, in the MANUAL mode, the temperature control is disabled and the heating element will run all the time.

Turn off your LP gas. put AC power on the coach.

Turn on the frig, then after a couple seconds, click the MANUAL button to force it into MANUAL mode using AC. The heater should run constantly, with no thermostat control.

There is a procedure to test the thermister in my book, but I think your 3662 is similar to my 2652.
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Old 08-24-2016, 11:20 AM   #7
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AS you are aware AC Mode can only be used when in AUTO
No manual AC mode.....manual mode only for GAS

So with fridge in AUTO, turned ON and 120V AC power source available Fridge will operated on electric heat element.
J7 & J8 S/B energized when in Auto/AC available fridge ON
J8 is lead that is 'switched' -------Circuit board AC relay
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Old 08-24-2016, 01:29 PM   #8
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J7 and J8 aren't giving me juice when Auto/AC and fridge on. With 120v available, when turning fridge on (in AUTO) it will wait for 2 seconds and go straight to gas. Could J8 be the culprit?

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AS you are aware AC Mode can only be used when in AUTO
No manual AC mode.....manual mode only for GAS

So with fridge in AUTO, turned ON and 120V AC power source available Fridge will operated on electric heat element.
J7 & J8 S/B energized when in Auto/AC available fridge ON
J8 is lead that is 'switched' -------Circuit board AC relay
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Old 08-24-2016, 05:36 PM   #9
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J7 and J8 aren't giving me juice when Auto/AC and fridge on. With 120v available, when turning fridge on (in AUTO) it will wait for 2 seconds and go straight to gas. Could J8 be the culprit?
Circuit board is bad.......could be ac relay, could be broken circuit, could be bad contacts

One thing for sure.....no 120V AC at J7/J8 circuit board is not functioning
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Old 08-25-2016, 03:53 AM   #10
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10-4.
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Old 08-25-2016, 04:00 AM   #11
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If the frig is trying to automatically switch over to LP when you know that AC is available, then it sounds like a bad controller board.

Remove the board and look very carefully to see if there is anything obvious that may be repairable.

I've run into bad solder pads where all I needed to do was re-flow the solder on a pad and we were good for a few more years.the AC is turned on
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Old 08-25-2016, 11:44 AM   #12
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Will do, Waiter. The controller board is the one on the fridge front, correct?

K

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If the frig is trying to automatically switch over to LP when you know that AC is available, then it sounds like a bad controller board.

Remove the board and look very carefully to see if there is anything obvious that may be repairable.

I've run into bad solder pads where all I needed to do was re-flow the solder on a pad and we were good for a few more years.the AC is turned on
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Old 08-25-2016, 01:26 PM   #13
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the board that you were testing J7 and J8. Mine is on the back, accessible from the outside.

Use you smart phone to take a couple photos of the board befor disconnecting anything.
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