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A bit of help if anyone can I've got a mdc 65 fridge that won't go any cooler than 3 degrees in the freezer part when it's running there is only about 4 inches of ice on the evaporator just after the end of the cap tube it was like that when I got it I was told it needed re gassing so I got it done but it doesn't seem to have made any change l am thinking that the cap tube might be blocked any replies welcome
Medion
Sounds like it could be a restriction in the capilary or maybe the filter, or maybe its just lost the gas again and a leak hasnt been repaired. Could also be that its been recharged to the wrong weight or even the wrong refrigerant.
With the correct refrigerant and weight charged in the system you would normally get a reasonably even frost over the plate evaporator after running for a bit. And the liquid line filter shouldnt have a temperature change from inlet to outlet, and should be at the same sort of temp as the condenser outlet.
If its the type of system Im thinking it is, if needed the filter shouldnt be to hard to replace but a blocked capillary might be more of a problem.
With the refrigerant charge being pretty small on those units its easy to over and under charge them.
Does the compressor just run all the time?
Is the compressor getting very hot?
Yes the compressor runs all the time it was charged with r134a if it's off overnight it works a little better first in the morning but if you stop it then start it again after a short time it won't go as cold the cap tube frosts as it leaves the filter dryer and where it enters the return line of the evaporator the condenser is quite cold apart from about 8 inches where it leaves the compressor but I think a lot of that is heat transfer from the compressor if its restricted is there any tests I can do to confirm
Thanks for your reply. Medion
To check it you would need to put atleast a pressure gauge on the suction side, and one on the discharge would be good as well. Again because you have such a small charge in those systems just putting a gauge line on can give a significant change to the system charge and pressures.
Another problem it could be is moisture in the system, which can give intermittent choking of the filter/capillary.
If it was me and I had access to gauges. I would first have the system running to pull the pressure low before switching the unit off, wait a wee bit to allow the low side pressure to hopefully just go above a vacuum, and then connect a low side/suction gauge using a short length gauge line. Then I would be leaving the unit off to allow the system pressure to equilise so I could check the standing pressure (can take some time with a choke). With the pressure equilised then I would be keeping an eye on the pressure and the temperatures of the pipework as it cools down, checking for the frost pattern on the evaporator and of the filter/capillary. The standing pressure and the running suction pressure would give you a rough idea of if its a choke or just low on gas, or something else.
If I was unsure what had been previously done to the system and had access to all the gear, and if it had a low suction pressure. I would be recovering the refrigerant from the system, giving it a leak check with nitrogen (if needed repair any leaks and check again), vacuum the system and check theres no moisture with a torr gauge, then with a gauge on the suction and discharge side I would be recharging it using sensitive scales and isolation valves on the ends of the gauge lines, with gauges on both sides see how it runs, then use the isolation valve on the dischage gauge connection to remove the gauge and allow the trapped refrigerant to be charged to the system to give near enough the correct charge, see how it runs with that. If I still got low pressures and frosting of the filter/capillary then you would be able to safely say theres a restriction there.
Anyway at the moment your probably at the point a fridge tech would be needed.
I have a low side gauge I will try it on tomorrow the problem with these fridges is because they run on 12v it's hard to find anyone to look at them thig is the first run of the day it seems to work a bit better but after a switch off then on it's not as good but I will take some notes and post back tomorrowQuote:
Originally Posted by seanf
Thanks for all the help. Medion
If you've got frost at the drier outlet then looks like the drier is blocked or partially restricted and needs replacing. Might be worth replacing the cap tube at the same time, save any grief.Quote:
Originally Posted by medion
Moisture in the system needs new drier a good vac and charging with fresh gas !
Transport Refrigeration repair companies might be the ones to try, they sometimes work on refrigerated cubes that get thrown in the back of vans which use the same 12V units. The same units are used for fridges on yachts, maybe you have a marina near by you could ask or search on a yacht forum.Quote:
Originally Posted by medion
Good cooling on the first run might just be from the refrigerant that collects in the evap while its off, along with a cool compressor. Or like redroge has said it could be moisture in the system that chokes it during the first run.
Just a bit of a update
52 psi at startup drops to 2 psi then rises to 20 psi and stays at that then when switched off it takes 16 minutes to equalise so I let the compressor cool down a bit then back on the ice box dropped to 2.2 degrees c but wouldn't get any cooler then off again and 16 minutes to equalise again
Thanks again. Medion
What sort of temperatures do you get at the discharge pipe, condenser outlet and evap outlet at the start, during and end of a run? What sort of run time are you talking about also.Quote:
Originally Posted by medion
Whats the temperature of the room the fridge is in?
Does the filter and capilary frost up/sweat straight away or does it slowly start at the evap inlet and work its way back to the filter?
Is it just the evap inlet that frosts heavily or does the full evap plate sweat?
Further update temprature testQuote:
Originally Posted by seanf
Condenser inlet 14.7 start 23.3@1min 24.9@3min 25.1@6min 25.4@9min 20.6@12min 17.9@14min 17.1@16min 19.0@18 29.3@52min 35.5@72 min
Condenser outlet 14.9 start 17.4@3 min 14.0@6min 12.4@9min 12.54@9min 12.5@12min 13.7@14min13.5@16min 13.6@18min 8.5@52min 3.2@72min
Evaporator outlet16.6 start 14.4@1min 14.3@3min 13.5@6min 3.3@9min 2.2@12min 2.5@14min 2.7@16min 2.5@18min 5.9@52min 5.2@72min
The dryer hasn't got any frost on it just the capillary after a couple of minutes
The evaporator plate frosts at the capillary end and about 4 inches of the first line on the plate there is no further frost on the plate I am not sure if the plate is sweating or just condensation I can't see if the frost travels down the capillary because it's covered by insulation but they probably frost at the same time
Thanks again medion
From what I remember working on this type of unit, the ones that were working well, they would first pull down the standing pressure to between just under 0psig to 5psig. With the box temp and evap still warm the pressure would build up to around 10-18 psig. With the evap mostly frosted and box cooling they would normally run 0-6 psig.Quote:
Originally Posted by medion
Temperature wise, most of them seemed to run with the condenser pretty cool. The compressors normally ran with a wee bit of warmth, some units the comps ran a bit too warm but still cooled well and had good suction line temps.
To me it sounds like its most likely got a restriction and its been slightly over charged.
what do you think the chances of there being any problems with the compressor in case I end up chopping the compressor out and getting it fitted to a small mains fridge I doubt I would get anyone to change the capillary if it was restricted at the evaporator end if it's just a matter of similar btu and it using r134aQuote:
Originally Posted by seanf
Thanks again for all your support
Medion
It could be that your unit has the correct charge, that it does have a restriction and the compressor isnt pumping as well as it should. I guess I would be looking at how quickly and well it pulls the pressure down from standing pressure. Having a gauge on the high side as well would help get a better idea of how well its doing also.Quote:
Originally Posted by medion
If I remember correctly, yer the capillary connection to the evap plate wouldnt be the easiest thing to do. I know that you can get replacement evaporator plates with the suction and capillary already connected.
That your getting frost at the start of the capillary reasonably quickly suggests its more likey to be restricted at the filter outlet or capillary inlet. You could cut the filter out and check it for a blockage and check the capillary inlet at the same time. You may also be able to get away with taking a very small length off the start of the capillary if its blocked the tip. You may also get lucky and find that someone has made a bad repair when changing the filter and pushed the capillary tube up against the filters outlet fine mesh screen.
For putting the 12V comp on a standard fridge you would need to match the compressors capabilities well. A compressor thats too small/big for the system can give you problems. You also need to think about things like, is the air flow from the condener fan part of the compressor cooling.
Some of these wee Danfoss 12V comps if I remember, may allow you to adjust there capacity through using different resistors on their control module for selecting different speeds, which may give you more options if you were to try and use it on another system.
Further update
Finally had the fridge done today the capillary was restricted at the drier end the capillary had been pushed to far in and was hard against the mesh so instead of a large area there was next to nothing after a little buildup so after a new drier it all seems to be working fine now
Thank you so much for the update.
It's the little things that can cause the biggest headaches.
Glad it's running again.