Old Dometic fridge cooling problem

Discussion in 'General RVing' started by sp, Sep 9, 2005.

  1. sp

    sp Senior Member

    The last two trips I've had a problem with the fridge staying cold the whole time. I fire up the propane the day before we leave and it is around 40 degrees when we are ready to go (overnight). I drive to the campground(s) (3 1/2 hrs and 1/2 hr trips) and the temp goes up. I level the unit and let it sit and the temp still is high (~4hrs). I switch to electric, which never seems to cool properly from day one about 3 years ago now, and it gets cool but not enough (over night). I switch back to propane and in a few hours it is at 40 again. There isn't a complete pattern of when it does this.

    I know: has to be level, it has worked properly for two years and two trips so this issue is recent (last two trips), may need to pull and clean, burner and jet, and the temp feeler by the burner is worn/burnt at the tip.

    Any ideas??

    Thanks,
    Steve
     
  2. Kirk

    Kirk Senior Member

    Old Dometic fridge cooling problem

    I hate to bring bad news, but I would suspect that the cooling unit of your refrigerator has lost part of it's coolant. The coolant in an absorbtion refrigerator is a mixture of ammonia and water. When it gets old one of two things will eventually happen. It can spring a leak and you usually know that because it will smell of ammonia and frequently have some yellow dust in the rear of the unit. The other thing that will happen if it is around long enough is that the ammoina will begin to crystalize and deposit into different locations, where it begins to restrict the flow of the coolant that does vaporize. Either of these will cause the cooling process to slow. The most apparent one is for the leak but since your refrigerator is now nearing 30 years old, it is highly likely that retirement is in order. There is probably not much that you can do to correct the problem, but to replace it. Most likely it will continue to deteriorate. It will operate better and for longer on propane as it is the greater hear source. Good luck! I will hope that I prove to be wrong on this one.
     
  3. C Nash

    C Nash Senior Member

    Old Dometic fridge cooling problem

    Check the flame for proper adjustment and also ck the flue for obstructions. Might try removing the unit and turning it upside down overnight. let us know what you find
     
  4. s.harrington

    s.harrington Senior Member

    Old Dometic fridge cooling problem

    what model do you have? (This is for non electronic controlled refers). Sounds like it could be your themostat has gone bad. However it could be that your cooling unit has an inlernal leak. Do you hear a perking soun like an old coffee pot when its running on electric (you'll have to be outside with the vent door open and your ear stuck inside by the area where the
    heating element goes)? If you do its probably your cooling unit. To check the t-stat you need an extra person. you take the t-stat metal tube out from under its holer @ the fins in the refer and put it in some icewater. The heighth of the flame should change. if it doesn't change it out.
     
  5. sp

    sp Senior Member

    Old Dometic fridge cooling problem

    It says in my book that it is a RM66e. It runs on electric or propane so it has two thermostats. I don't think it is an internal coolant leak because I don't hear that any perculating noise and it also stays cold for periods of time. It has never really worked well on electric so I'm thinking what Kirk said about propane being the better heat source. I do need to have someone help me check the level of the flame as I move the temp controller from 0 to max. I'll also have to check for cobwebs that may have blocked the flue. I'm going to wait to here from others to see if I get a reoccuring theme and then head there first.

    Thanks for all the info.
    sp
     
  6. sp

    sp Senior Member

    Old Dometic fridge cooling problem

    Well, I finally got some time to play around with this. I removed the metal around the feeler,jet and burner and blew some air through it. I tried to check the stack from down below but it was loaded with insulation so I just put it back together. I didn't have time to pull it and do C Nash's flip trick. I set the thermostat to max to see if the flame was any higher than at setting 4 but it was hard to tell because you can't really see up the stack. The burner actually sounded different at the higher and lower settings and when I checked it at night you could see that the flame was narrower on 4 and wider on max. On max it got down to 20 degrees so I played with the settings until it kept a constant of 38 degrees for 2 days straight.

    Lets see if it works this well when I need it, this weekend. I'm putting its retirement on hold for now. ;)

    Thanks, sp
     
  7. Kirk

    Kirk Senior Member

    Old Dometic fridge cooling problem

    It does sound as though you do have a good cooling unit, and that is good news! A couple of things of note.

    First of all, the temperature setting of your refirgerator does not change the flame that boils the coolant in any way. What it does is to determine the temperature at which it shuts off. When you lower the temperature it just means that the cooling will stay on to a lower temperature setting before it turns off and it will reignite the flame at a lower temperature than it would have when set to a warmer setting. But the flame is not turned up or down like it is on a stove top. It is either on, or off. I would suggest that you get a good shop vacume and clean everything that you can with it. If there is a tool that you can reach up into the stack, that too is a good idea. If not, blow the stack with compressed air and then use the shop vac to remove what falls down into the flue area. It is normal for the inside of the chimney to rust and that rust could be a major part of your problem.

    Locate the electric element. It will have two leads that come from it to the circuit board of the refrigerator. I would unplug the AC power plug before I did anything with that part, for safety. Once you unplug it, trace the two leads from the circuit board that go to the same general area as the propane flame is located. The element is usually located near the propane flame, but above it. It can be removed and cleaned. If it looks to be in poor condition, they are not difficult to clean or to replace. And they should not be very costly either. While you have it out, apply the shop vacume to the opening for it as well. While you have the vacume applied to the hole, tap gently on the flue with a rubber mallet or some plastic item to loosen any rust, but using care not to dent the flue. Rust can cause the electric element to work poorly and it is only about 1/2 to 2/3 of the heat output of the propane flame under the best of circumstances.

    Good luck! It does sound as though you are making progress.
     
  8. Just BeClaus

    Just BeClaus New Member

    Old Dometic fridge cooling problem

    Very Good "Kirk" you hit the nail on the head or the flu.. But I thought that the cooling unit was a mixure of ammonia and hydrogen. That when they go bad the hydrogen leaks out first cause it is a thinner gas then the ammonia (clears your sinus out) when they are bad. I could be wrong on this but it makes since.. Just BeClaus
     
  9. Johnny-O

    Johnny-O New Member

    Old Dometic fridge cooling problem

    YOU MIGHT WANT TO TEST THE HEATING ELEMENT WITH AN OHM METER. I'M NOT SURE WHAT THE RESISTANCE SHOULD READ, SOMEWHERE AROUND 40 OHMS. MOST SHOPS HAVE A BOOK WITH ALL THIS INFO, IF THE HEATING ELEMENT IS BREAKING DOWN, IT WONT GET HOT ENOUGH TO BOIL THE AMMONIA AND WATER. AFTER 30 YEARS HEATING ELEMENTS WILL TEND TO BREAK DOWN.
     
  10. sp

    sp Senior Member

    Old Dometic fridge cooling problem

    Boz, is there a chance that the themostat is fluctuating? What is the actual name of the heating element. I have the original oweners manual and diagram of parts. There is one side for electric and one for gas. So the gas side has nothing to check with the meter. Maybe i jsut don't understand if you just want me to test the electric side.
    thx sp
     
  11. Johnny-O

    Johnny-O New Member

    Old Dometic fridge cooling problem

    Hi SP, I understand you might be a little confused, so I'll try to explain. The thermostat is simply an on/off switch. When the refer cools to a preselected temp. the t-stat shuts off the energy source, whether it's gas or electric. Some older models have a high/low type valve, but only because they lacked an electronic ignition system. If the flame went out, you had to relight it manually. If your refer works better on one energy source than the other, the problem is more likly the energy source, not the t-stat. To check the "Heating Element", first (as Kirk suggested) unplug the AC cord. Remove the two wires from the control board leading to the heating element. Set your meter to OHMs, at it's lowest setting, (Rx1 for analog meters). Attach your leads to the wire ends and note your OHM reading. Your manual should give you the correct OHM reading. If not, talk to your dealer, or look up the Dometic web site. RV refers have no moving parts and rely on a chemical reaction to work. A precise heat range is critical for the refer to cool. You might also have your LP pressure checked, This requires a special guage called a "monameter". Any shop can do this, and it only takes a few minutes. A high LP pressure creates to much heat, and can cause the cooling unit to crystalize, blocking the plumbing. Anyway, I hope this helps. Good luck. By the way guys, there are 4 elements in a cooling unit, amonia, hydrogen, water, and the yellow stuff. Never could remember the name of that stuff. But the only reason it's there is to indicate a leak in the cooling unit. The Boz
     
  12. Johnny-O

    Johnny-O New Member

    Old Dometic fridge cooling problem

    Hi SP, I understand you might be a little confused, so I'll try to explain. The thermostat is simply an on/off switch. When the refer cools to a preselected temp. the t-stat shuts off the energy source, whether it's gas or electric. Some older models have a high/low type valve, but only because they lacked an electronic ignition system. If the flame went out, you had to relight it manually. If your refer works better on one energy source than the other, the problem is more likly the energy source, not the t-stat. To check the "Heating Element", first (as Kirk suggested) unplug the AC cord. Remove the two wires from the control board leading to the heating element. Set your meter to OHMs, at it's lowest setting, (Rx1 for analog meters). Attach your leads to the wire ends and note your OHM reading. Your manual should give you the correct OHM reading. If not, talk to your dealer, or look up the Dometic web site. RV refers have no moving parts and rely on a chemical reaction to work. A precise heat range is critical for the refer to cool. You might also have your LP pressure checked, This requires a special guage called a "monameter". Any shop can do this, and it only takes a few minutes. A high LP pressure creates to much heat, and can cause the cooling unit to crystalize, blocking the plumbing. Anyway, I hope this helps. Good luck. By the way guys, there are 4 elements in a cooling unit, amonia, hydrogen, water, and the yellow stuff. Never could remember the name of that stuff. But the only reason it's there is to indicate a leak in the cooling unit. The Boz
     
  13. Johnny-O

    Johnny-O New Member

    Old Dometic fridge cooling problem

    Hi SP, I understand you might be a little confused, so I'll try to explain. The thermostat is simply an on/off switch. When the refer cools to a preselected temp. the t-stat shuts off the energy source, whether it's gas or electric. Some older models have a high/low type valve, but only because they lacked an electronic ignition system. If the flame went out, you had to relight it manually. If your refer works better on one energy source than the other, the problem is more likly the energy source, not the t-stat. To check the "Heating Element", first (as Kirk suggested) unplug the AC cord. Remove the two wires from the control board leading to the heating element. Set your meter to OHMs, at it's lowest setting, (Rx1 for analog meters). Attach your leads to the wire ends and note your OHM reading. Your manual should give you the correct OHM reading. If not, talk to your dealer, or look up the Dometic web site. RV refers have no moving parts and rely on a chemical reaction to work. A precise heat range is critical for the refer to cool. You might also have your LP pressure checked, This requires a special guage called a "monameter". Any shop can do this, and it only takes a few minutes. A high LP pressure creates to much heat, and can cause the cooling unit to crystalize, blocking the plumbing. Anyway, I hope this helps. Good luck. By the way guys, there are 4 elements in a cooling unit, amonia, hydrogen, water, and the yellow stuff. Never could remember the name of that stuff. But the only reason it's there is to indicate a leak in the cooling unit. The Boz
     
  14. ARCHER

    ARCHER Senior Member

    Old Dometic fridge cooling problem

    Hey Boz,
    What is considered too high for LP pressure? I've got a pressure gauge on my ole 89 Winnebago Chieftain that I can monitor for pressure and leaks, but was just wandering what is a normal pressure for LP (+/-)
     
  15. Johnny-O

    Johnny-O New Member

    Old Dometic fridge cooling problem

    Hi Archer,
    All RV apliances are designed to operate at 11 inches water column +/- 1/2 in.
    The Boz
     
  16. ARCHER

    ARCHER Senior Member

    Old Dometic fridge cooling problem

    Hey Boz, thanks for the info. I'll check it after I get to Texas next week for the winter.
     
  17. Gary B

    Gary B Senior Member

    Old Dometic fridge cooling problem

    Hey Archer, Have a good and safe trip to Texas, let us know how your doing there!!!! :) :approve:
    I know you told us but I forgot just where are you going in Texas? :sleepy: :(
    Have good one GB
    :) :laugh: :cool: :bleh: ;) :approve:
     
  18. ARCHER

    ARCHER Senior Member

    Old Dometic fridge cooling problem

    Hi Gary, Hope all is well with you and yours.
    Port Isabel/South Padre Island Texas is our target....we're pulling out tomorrow am real early. gonna stop at Graceland (never been there) and just take our time getting down South. Our reservations at Port Isabel are not until 1 Dec.
    Have a good and safe winter. :) :laugh: :cool: ;)
     
  19. SnowbirdInFlight

    SnowbirdInFlight Senior Member

    Old Dometic fridge cooling problem

    What RV park in South Padre? We'll be heading down that way in about 4 weeks. South Padre's a little high isn't it? At least compared to further inland. Does the place you stay at have Cable T.V. and Internet hook-ups?

    Gee I wish we could leave now, but we have to wait for the last litter of pups to be sold first. :(
     
  20. Grandview Trailer Sa

    Grandview Trailer Sa Senior Member

    Old Dometic fridge cooling problem

    Snowbird, What type of pups?
     

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