Common complaints, refrigeration technician added too much refrigerant. Poor performance and frost on refrigerant line returning to compressor
Things to remember if
refrigerant level is in question:
1. Stop compressor and remove a very, very small amount of refrigerant. Run system 15 minutes, then check frost line it should not extend on un-insulated line more than a few inches outside refrigerated box in cold weather, in warm weather only condensation should be present outside the box. If there is still too much frost stop compressor and repeat process. When operating properly there must be a layer of ice forming over 90% of evaporator’s surface. If too much refrigerant is removed there will be an area of the evaporator without frost.
2. Once the system is operating OK set the thermostat to full cold for at least 12 hours. If at the end of this test run evaporator has lost its frost and evaporator is cold with only condensation on it there is moisture in the refrigerant.
3. If letting out refrigerant did not solve the performance problem or system freezes up due to moisture, a refrigeration vacuum pump will be required to remove air, moisture or incorrect gases.
I don’t like to connect gauges to a system until I have proven that the
refrigerant is the problem. Make sure there is adequate airflow through the
condenser. If your evaporator is a thin aluminum plate and not an Adler Barbour
Power Plate the frost line will indicate if the refrigerant charge is correct.
When there is sufficient refrigerant there will be frost covering 90% of the
evaporator’s surface and no bare spots. One half an ounce too much refrigerant
on a small cap tube system could double the daily amp-hrs consumed, see chart on
page 56 in 12/24 volt book.
Adler Barbour’s new super cold machine with BD 50 compressor has the same
components as the cold machine except the super unit has a small supplemental
water condenser on liquid pressure line. Servicing a DB50 with a capillary tube
expansion device is the same as servicing your old BD compressor except with
134a there is a small pressure difference. If you do need to add refrigerant
follow the steps listed on page 58 and 59 to the letter and you will end up with
an efficient system.
A frequent problem that occurs when servicing a 12/24 volt small refrigeration unit is that you or a service tech has added too much refrigerant to the system. While the unit is overcharged, check to see if there is frost on the return line and a 3 LED signal. This will confirm that too much refrigerant has been added. The first thing that you must do is to check for any leaks that might have been overlooked prior to servicing.
First check for any leaks: The areas to check for leaks on AB Cold Machines are: mechanical line connections, the three refrigerant service connection leak proof caps and line connections at the power plate, if you have one, instead of a standard aluminum evaporator.
By using a one inch paint brush and a 50/50 mixture of liquid soap and water you will be able to find leaks as small as a ½ ounce per six months if you follow these instructions:
If one of the serving caps or line connectors are leaking, use two wrenches to tighten but never tighten any tighter than what it takes to stop the leak. Some of the power plates have O rings as seals so in order to stop a leak there, it may be necessary to remove the refrigerant and replace the O ring seal.
To correct an overload - indicated by frost on the return line and confirmed by three LED flashes, do the following:
After two or more hours running time the evaporator’s surface area should be covered 95 to 100% covered with a thin layer of frost with no frost on the return line outside of the refrigerated area on the line towards compressor.
After 40 years in the tool and die business, I have switched professions to Marine canvas and Marine Refrigeration. Just today I was asked to charge an older AB system and found the compressor much warmer than I liked. I found the low side at 16 psi and compressor amperage at 7.6 equalized pressure on this system was 40 psi
I bled the system down to 7-8 psi and normal ranges prevailed.
My question may be more ethical than technical but this system was apparently charged by someone who didn't know where they were heading. Would it be prudent to advise the customer to pay for a recovery and deep vacuum with recharge to eliminate the possibility of air from lines they may not have bled properly . I don't know how many times they may have opened the system.
Answer: I hear of at least two systems a week that have been serviced incorrectly. The first thing to determine is why it was necessary in the first place to tamper with refrigerant level. In many cases poor or no cooling performance relates an electrical problem with boat wiring or Danfoss compressor and not refrigerant volume. Once the decision is made to connect gauges to one of these small systems the door is open to major contamination problems. If refrigerant was truly needed then there is a leak and it needs to be found before evacuating and re-servicing. In the last twenty years I never charged for a service call to add refrigerant to one of these systems if I could not confirm and repair the leak.
4. Servicing BD (Variable speed compressor)Too much refrigerant ?
unit is destined for service. It cools my 8cft freezer box, and I have installed
a new CU-200 and vd -162 in the refrigerator portion- which is approximately
12-14 cuft with 4" insulation. For the fridge, I bought the evaporator new, but
the compressor deck was 1 year old and had been used for that period. I removed
the old couplings and soldered on new, also soldered on a new filter/dryer and
then vacuumed the unit and charged it to the max it would hold with 134a. I then
vacuumed it again and recharged to the max it would accept (65 psi) with 134a
again. At that point I connected the unit to the evaporator per the
5. Too much Refrigerant Now what do I Do?
The unit I
have is a cu-200 from 2006. It is a BD50. The thermostat capillary tube is
correctly installed and the refrigerant tube frosts back about 5 feet. When it
exits the box, there is no frost line, only inside the box.
Five ft of frost on the return line would indicate too much refrigerant on that manufacturer’s condensing unit and evaporator. Refrigerant volume is very critical on a refrigerator that incorporates a capillary tube expansion device and there is very little room for error if energy efficiency is important. To pre-charge your system, to a specific volume by weight is not possible for you to do. The only way to service your unit is by suction pressure, frost line or amperage. Assuming there are no restrictions in any connections you made in tubing (soldering small tubes together can cause blockage}, and refrigerant is 134a. Here is what to do to relieve the over-charged condition:
6. Servicing BD35 Another overcharged system
First, thanks for all
your help and such a great web site. Both your books have been a great help.
7. Return Line Icing Too Much Refrigerant
Why do I have frost on my refrigerant line all the way back to compressor?
Answer: Adler Barbour and other similar ice box conversion units supply a three foot piece of insulated tubing to use on the lines just outside the box. In moderate temperatures and humidity three feet of insulation should be enough to prevent moisture on the lines outside the box. There is one condition that will produce frosting on the return line and extend the compressor running time, and that is too much refrigerant in the system. The factory refrigerant charge will not cause this condition but if the system was field serviced with refrigerant that could cause the problem you describe.
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