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A mate of mine has turned up with a small fridge which he has removed from his motorhome which will not run. Its a 12v jobby and consists of a thermostat which has a red reset button located on the thermostat panel, a cylindrical Compressor and a PCB which is a oscillator board. I have checked the thermostat and thats fine but the compressor has two connections which come from the PCB Oscillator baord and the compressor appears to be down to earth in that I can read a circuit between the main casing and two compressor terminals ? This all be Negative earth on a vehicle this does not seem right but has anyone worked on these sort of things ?
How does the PCB operate the Compressor ? additionally are spares available for these as the things made in japan or china and are they cost effective to repair ?
Thanks
Re: Caravanette and Motor Home Fridges ?
You’ll probably find the “cylindrical compressor” houses a heater and the fridge is the (very) old-fashioned absorbtion type, full of an ammonia based refrigerant. the pcb is more than likely a changeover device enabling the fridge to work off mains or 12v dc when connected to the auxilliary socket at the rear of the towing vehicle.
Re: Caravanette and Motor Home Fridges ?
Single pressure absorption refrigeration[edit]
Labeled photo of a domestic absorption refrigerator.
1. Hydrogen enters the pipe with liquid ammonia
2. Ammonia+hydrogen enter the inner compartment of the refrigerator. Change in partial pressure causes ammonia to evaporate. Energy is being drawn from the surroundings – this causes the cooling effect. Ammonia+hydrogen return from the inner part, ammonia returns back to absorber and dissolves in water. Hydrogen is free to rise upwards
3. Ammonia gas condensation (passive cooling)
4. Hot ammonia (gas)
5. Heat insulation and separation of water from ammonia gas
6. Heat source (electric)
7. Absorber vessel (water + ammonia solution)
A single-pressure absorption refrigerator uses three substances: ammonia, hydrogen gas, and water. At standard atmospheric conditions, ammonia is a gas with a boiling point of -33°C. The system is pressurized to the point where the ammonia is liquid. The cycle is closed, with all hydrogen, water and ammonia collected and endlessly reused.The cooling cycle starts with liquefied ammonia entering the evaporator at room temperature. The evaporated ammonia is mixed with hydrogen. The partial pressure of the hydrogen is used to regulate the total pressure, which in turn regulates[clarification needed] the vapor pressure and thus the boiling point of the ammonia. As the ammonia boils in the evaporator, it pulls heat from the refrigerator’s interior and provides the cooling required.
The next three steps exist to separate the gaseous ammonia and the hydrogen:
1.In the absorber, the mixture of gases enters the bottom of an uphill series of tubes[why?], into which water is added at the top[how?]. The ammonia dissolves in the water, producing a mixture of liquid ammonia solution and hydrogen. The gaseous hydrogen collects at the top of the absorber, while the liquid ammonia solution flows to the bottom.
2.The next step separates the ammonia and water. In the generator, heat is applied to the solution to distill the ammonia from the water. Some water vapor and bubbles remain mixed with the ammonia. This water is dried out in the final separation step, by passing it through the separator, an uphill series of twisted pipes with minor obstacles to pop the bubbles, allowing the collected water to drain back to the generator.
3.Finally, the pure ammonia gas enters the condenser. In this heat exchanger, the hot ammonia gas is cooled to room temperature and hence condenses to a liquid[clarification needed], allowing the cycle to restart.
(copied from Wickipedia)Re: Caravanette and Motor Home Fridges ?
Uploaded with ImageShack.us
Labeled photo of a domestic absorption refrigerator.
1. Hydrogen enters the pipe with liquid ammonia
2. Ammonia+hydrogen enter the inner compartment of the refrigerator. Change in partial pressure causes ammonia to evaporate. Energy is being drawn from the surroundings – this causes the cooling effect. Ammonia+hydrogen return from the inner part, ammonia returns back to absorber and dissolves in water. Hydrogen is free to rise upwards
3. Ammonia gas condensation (passive cooling)
4. Hot ammonia (gas)
5. Heat insulation and separation of water from ammonia gas
6. Heat source (electric)
7. Absorber vessel (water + ammonia solutionRe: Caravanette and Motor Home Fridges ?
And when they stopped working usually tipping upside down a few times would cure them.
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Re: Caravanette and Motor Home Fridges ?
lee8 wrote:And when they stopped working usually tipping upside down a few times would cure them.
But not if the heater ain’t working. Does it get hot at the back Squady? From what you tell us I think not.
Re: Caravanette and Motor Home Fridges ?
Martin no it does not get hot, I will upload a picture of the rear to see if it makes it any clearer re design.
Re: Caravanette and Motor Home Fridges ?
Some interesting reading that may help
http://www.sawafuji.co.jp/english/index.html
http://www.sawafuji.co.jp/english/tech/shindou.html
http://www.roadtrucker.com/engel/engel-12-volt-fridge-freezer-technical.htmlRe: Caravanette and Motor Home Fridges ?
squadman wrote:
Walk away from it, slowly, turn and run away!!
Re: Caravanette and Motor Home Fridges ?
jag-12 wrote:Some interesting reading that may help
http://www.sawafuji.co.jp/english/index.html
http://www.sawafuji.co.jp/english/tech/shindou.html
http://www.roadtrucker.com/engel/engel-12-volt-fridge-freezer-technical.htmlThanks Jag, very helpful !
Re: Caravanette and Motor Home Fridges ?
Jag,
As you are over in Devon do you repair these ? being surrounded by Camp sites etc it may be that you see a lot of these ?
Cheers
Re: Caravanette and Motor Home Fridges ?
Looks like an integral piece of frankeinstein’s laboratory.
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Re: Caravanette and Motor Home Fridges ?
Saw this thread and thought 30 years of absorption work might help!
Unfortunately not, looks to me like a rotary compressor as there is a standard condenser, unlike the absorption ones.
The electrical device is likely to be some type of inverter combined perhaps with a switch over from 240 to 12 volt, .The reasons these compressors are used is for quiet starting and running as folks will be kipping a few feet.
Have seen a couple of similar one’s in marine/boat installations
Check the wattage on the motor label and using ohms work out the resistance.
Also you could disconnect the motor lead, check the compressor label for voltage and type, connect your meter, set correctly, switch on and check the voltage on your meter.
If you can put a picture of the terminal entries into the compressor up it would help.
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