A common issue with the absorption refrigerators fitted to most motorhomes is insufficient cooling performance when operating on gas. Absorption fridges are interesting devices that cool using no moving parts, and require only heat to drive the cooling process (which seems counter intuitive, but if you want to read more about the working principles Wikipedia has a good article here)
A 3-way fridge will operate on 12V, 240V (or 120V) and gas. All three energy sources simply create the required heat, so if you fridge is working OK on electricity but not on gas you know the refrigeration part is working correctly, but you are not getting the required heat from the gas burner. What is most likely the problem is that either the gas supply or the flue is blocked to some degree, so we need to get access to the back of the fridge to check it out.
On a lot of vehicles there are two fridge vents on the outside of the vehicle that can be removed for access to the rear of the fridge for inspection of the burner, flue etc.
Note – On our Hymer B544 the rear vent is behind the rear bumper so I took the fridge out completely to inspect it – there is a write up on how to remove the fridge here
At the rear top of the fridge is the main heat exchanger and flue outlet for the gas burner – make sure these are clean (a soft brush and a blow gun on an air compressor are good for removing built up dust etc.)
To the right of this image is the flue outlet, secured in place by one screw. With this removed you can lift out the spiral baffle from the flue and look down the flue for blockages/debris
At the bottom right you will see a cover box that enclosed the burner, igniter and flame sensor, remove this for access to the burner
Here is the burner assembly removed from the bottom of the flue (held in place by one screw), with the gas pipe unscrewed from the assembly. With this removed the whole flew should now be clear and can be cleaned with a pipe brush or similar if required
Here you can see the end of the gas supply pipe, this can become blocked with carbon deposits
To ensure the gas pipe is clear it can also be disconnected from the gas valve on the top of the fridge, you can them blow down it with compressed air – I also used some aerosol brake cleaner to flush it out.
Here you can just about see the small hole in the gas jet, this is the most likely part to be blocked – I cleaned this out with brake cleaner and compressed air
With the system cleared out and reassembled I once again had a fully functioning fridge.
Hopefully this helps you! – if you have any questions or comments please leave them below
UPDATE – we recently had another fridge issue where the baffle had dropped in the flue preventing the gas burner from igniting, you can read about that here.
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