12V problem with dometic RM2553

Submitted: Monday, Nov 30, 2015 at 14:14
ThreadID: 131014 Views:2115 Replies:1 FollowUps:6
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I have the dometic three way fridge and it has worked just fine for the last 7 years - I did replace a 240v heater a couple of years back. It has just stopped working on 12v and I was wondering if it is the 12v element or could I look at other possible problems before I buy a new element?
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Reply By: Allan B (Member, SunCoast) - Monday, Nov 30, 2015 at 14:32

Monday, Nov 30, 2015 at 14:32
A failed 12v heater is a likely possibility but before you purchase a replacement, are you able to use a multimeter to test the existing heater? I can offer instructions if you possess a multimeter.
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Allan

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Follow Up By: Jim W6 - Monday, Nov 30, 2015 at 18:12

Monday, Nov 30, 2015 at 18:12
Yes, I do have a multimeter and would appreciate your assistance. Cheers.....Jim
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Follow Up By: Allan B (Member, SunCoast) - Monday, Nov 30, 2015 at 18:58

Monday, Nov 30, 2015 at 18:58
OK Jim,

There can be a number of reasons for the 12v option to not work....... thermostat, wiring connections, supply problems...... but let's start with the 12v element itself.

First, be sure that the 230v supply is isolated.
1) Then locate the 12v element and disconnect it from the wiring
2) Turn your multimeter to the 'Resistance' mode. this may be marked as 'Ohms' or the omega symbol. With the leads apart it should be reading 'High' or 'OL' or such but not a numeric reading.
3) Touch the multimeter leads together and it should read 0.1 or 0.2 Ohms which is the resistance of the leads.
4) Hold the multimeter leads onto the terminals of the heater. The meter should read in the order of 2 or 3 Ohms. If the reading is much higher than this, even 'OL' perhaps, then it indicates that the heater is open-circuit, i.e. burnt-out, and will need to be replaced.

Try the above and report back before I complicate it with other possibilities.
Cheers
Allan

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Follow Up By: Jim W6 - Monday, Nov 30, 2015 at 21:01

Monday, Nov 30, 2015 at 21:01
Thanks Allan....I will get back to you once I have checked out the multimeter readings. Cheers....Jim.
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Follow Up By: Phil 23 - Tuesday, Dec 01, 2015 at 07:35

Tuesday, Dec 01, 2015 at 07:35
On a side note,
I'd also suggest that everyone that owns a multimeter should also invest in a simple screwdriver type test light.

Like this.


I usually replace their standard 24v bulb with a 12v one. Think mine has a 10w festoon, so would draw a bit under an amp.

As everyone that understands electronics will know, multimeters have a very high input impedance and can give false indications to people who don't fully understand electronics & Ohms Law, voltage drops across resistance.

A test light will draw current, & put a small bit of load on the circuit, which is often a more appropriate test.

Even with a long background in electronics, the test light is always my first go to tool when checking out 12v stuff, then pick up the Fluke if it's needed.

Cheers.
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Follow Up By: Allan B (Member, SunCoast) - Tuesday, Dec 01, 2015 at 08:32

Tuesday, Dec 01, 2015 at 08:32
Yes Phil, you are absolutely right. The test lamp is by far preferable when 'voltage hunting' and more convenient than a meter.
Mine differs only by having a 33 Ohm load resistor and couple of LED's for ruggedness, having broken glass lamps in the past. But the one you show would be rugged enough.

Of course, it won't measure resistance in an unpowered circuit where a meter is called for.
Cheers
Allan

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Follow Up By: Phil 23 - Wednesday, Dec 02, 2015 at 07:36

Wednesday, Dec 02, 2015 at 07:36
That's one of the best I've found. A Toledo from Super Cheap. I just ditch the 24 volt bulb.

Also great to check power either side of blade fuses to check if they are blown.
Some people my not be aware that you can test voltage either side of a fuse from the exposed contacts at the top. Seen either side of the "10".
Earth the test light, and if the lamp light on one side of the fuse & not the other then it's blown.


Also handy to carry a short wire with 3 blade connectors, so the test light can be connected in the place of a blown fuse to check for short circuits.

I also carry a meter Alan, but agree the test light with some load is much better for "Voltage Hunting".

Have also used a tone trace to try following some wiring in the van.....
Now that was recipe for going on a wild goose chase.

The tone traces & the nature of the wiring was just a no go.
Bloody tones popping up everywhere they shouldn't.
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