Dometic 2510

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Pickledboater

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My Dometic 2510 fridge in our truck camper has started freezing every thing when in A/C mode. Works as it should on gas. On gas, set on 3-4 ish it keeps the fridge at 38. On electric, even on 1 it freezes (right around 28-30). It would probably get even colder if I didn’t open the door often. The outside temperatures this weekend were in the high 70s during the day and mid 50s at night. I’m thinking thermostat, but wanted some opinions before I drop $85.00 on a new stat. What say you-all?
 

JayArr

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Before you go spending a bunch of money on a new thermostat...

I have the RM2510 and it uses the same thermostat for both AC and propane. I don't see how a thermostat capillary could affect one and not the other but it's possible the contacts in the thermostat housing could be arced/shorted together or that the capillary bulb no longer causes them to separate.

It sounds like the AC heater is stuck on all the time, you could confirm this with a voltmeter.

Cut power to the fridge and disconnect the heater from the thermostat and then hook up your meter to the thermostat terminals and set it on ohms or continuity. Vary the thermostat control and see of the contacts make and break of if they stay connected all the time.
 
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Gary RV_Wizard

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Agree with JarArr. Same thermostat for both, so any thermostat issue effects both. However, I see the thermostat control has seprate terminals for LP and AC modes, so maybe some difference becasue of that?

From the description it appears that the AC heater comes on and stays on, causing a freeze-up. If the relay was stuck it would also use AC to cool while in LP gas mode (assuming 120v is available to the RV), so I'm guessing the circuit board isn't responding to the thermostat when in AC mode. It just closes the AC relay and leaves it that way.

Note that #11 in the 2510 Troubleshooter is thermostat wiring, not the thermostat itself.
 
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JayArr

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No circuit board in an RM2510 Gary.

It has a separate reigniter block but it is self contained and on my unit it was white and filled with potting epoxy. Even if the reigniter block fails you can manually light the pilot and the unit will run on propane. It just takes two people since the pilot button is on the inside with the controls and someone else needs to be outside with a match.

The AC heater is controlled with a set of contacts that are opened and closed mechanically by the capillary bulb. At the same time as the contacts are opened or closed the propane valve opens or closes. Since the unit works on propane I assume the capillary bulb is working.
 

Kirk

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Agree with JarArr. Same thermostat for both, so any thermostat issue effects both. However, I see the thermostat control has seprate terminals for LP and AC modes, so maybe some difference becasue of that?
Did you look at the troubleshooting chart in the service manual that I posted a link to?
 

Pickledboater

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Great information Fellas! I’ll check the thermostat wires with my meter tomorrow when I get home. Any idea where the relay for the heater unit would be located? Or is the thermostat just wired directly to the element? I’m just glad that it has at least “failed” on and not the whole cooling unit shot!! We’ll get Er figured out.
 

JayArr

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There is no relay, it's old school, the thermostat just has a set of contacts that the heater attaches to.

Download the manual, it's easy to find with google and it has wiring diagrams and connection diagrams.
 

Henry J Fate

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No relay or control board.

Must be a bad thermostat. It is a 2 pole thermostat. The switching contacts for the ac mode are not opening but the gas mode contacts are still opening and closing properly.

Easily checked with a multimeter.
 

JayArr

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You're right about the heater contacts not opening Henry but it's a single pole thermostat, there are no "gas mode" contacts, the thermostat mechanically opens the propane valve and that is working properly.

Reading Henry's post made me go look at the manual again and now that I think about it the contacts in the switch must be working properly what you need to test is the contacts on the thermostat. They should close if you hit the thermostat capillary bulb with a hair dryer and open if you hold an ice cube on it.

The only other possibility I can think of is a long shot, if the polarity of the AC to the fridge was reversed ( line for neutral) and the heater element shorted to the frame it could stay on irregardless of the thermostat contacts.
 

Henry J Fate

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You're right about the heater contacts not opening Henry but it's a single pole thermostat, there are no "gas mode" contacts, the thermostat mechanically opens the propane valve and that is working properly.

Reading Henry's post made me go look at the manual again and now that I think about it the contacts in the switch must be working properly what you need to test is the contacts on the thermostat. They should close if you hit the thermostat capillary bulb with a hair dryer and open if you hold an ice cube on it.

The only other possibility I can think of is a long shot, if the polarity of the AC to the fridge was reversed ( line for neutral) and the heater element shorted to the frame it could stay on irregardless of the thermostat contacts.
Ah. I did not have time yesterday to pull up the cut sheet on that thermostat but I thought Gary posted that the thermostat had 2 sets of wires. If not then I guess it's the mode switch that changes the thermostat duty from gas to electric and the thermostat uses the same switching contacts for both 12 volts (gas mode) and 120 volts (electric mode). In that case then it seems unlikely to be the thermostat unless the contacts are acting different when higher voltage and higher current is applied when using electric mode.
 
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Henry J Fate

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Looked at the wiring diagram. It appears quite difficult to create a set of circumstances where the gas option is cooling properly but the electric option is freezing everything.

Assuming everything is wired properly and the electric element is good, the selector switch is where the 2 or 3 modes have dedicated contacts but it doesn't seem possible to create the event at the selector switch.

A short at the electric element is possible and should be checked with a multimeter.

The other possibility is that the gas burner is not cycling either but the thermal impact is not as great as the electric element for reasons as simple as a low gas pressure , bad nozzle, bad airflow etc. In this case the thermostat could be bad and is not working at all.

Using a multimeter on the thermostat should provide the answer as to whether the thermostat is working or not.
 
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Pickledboater

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All roads leading to the thermostat. Found a supplier that I can get one through and it looks easy enough to change. I’ll have to pull the fridge out a few inches so I can get my hands in behind it to fish the capillary wire but that would be the only hang up.
Il
I’ll update as it goes. Thanks for the info guys!!!!
 

JayArr

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get some telephone wire and attach it to the old thermostat before you pull it out then attach the new thermostat to it to pull it into place. IIRC there isn't much space for a hand up there and you have to remove the whole fridge to get the cooling unit out of the way.

Good luck, let us know if this solves the problem.
 

JayArr

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Yes, maybe too much so. Keep in mind it's a hollow tube, it can be kinked in a way that ruins it and it can also split and leak which ruins it. You want nice graceful curves, no 90's if you can help it and be delicate.

You have the advantage of pulling a bad one out, you can play with it, kink it, work it back and forth and get to know how it bends and how much force it is too much before you put the new one in.
 

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