This Old Refrigerator

Editor’s note: The August 7 Service Hotline included a question and answer about an old refrigerator. Since that appeared, we have received an additional answer. Here we repeat the original question as well as the latest response.


From Alvertis Bledsoe Marianna, AR

I have a General Electric monitor top refrigerator that is more than 50 years old. The nameplate shows sulfur dioxide was in it. The compressor still works, but there is a hole in the coil due to rust.

I want to know how I can restore this unit. Since sulfur dioxide is no longer available, can I use another refrigerant?


By Henry Ehrens Senior Engineer Sealed Unit Parts Co. Allenwood, NJ

I actually overhauled a monitor top about 50 years ago. It was a very challenging experience. The following is what you will be up against.

  • There isn’t any alternative refrigerant for sulfur dioxide. You may be able to obtain a few pounds from a chemical house. This is a very toxic gas and extreme caution must be used when handling it.
  • You have to obtain a special service valve that fits over the high- side float before you do any repairs.
  • Since you state that you ran the unit, air was taken in and must have built up a pressure in the dome. If you turn the setscrew on the high-side float very carefully, you will feel the pressure. Keep your face away.
  • It would be best to bleed the pressure outside the premises.
  • The evaporator leak should be repaired using a brass or silver welding rod.
  • Since the suction line of the evaporator goes directly into the unit, there isn’t any service access to the low side. The only means of testing the evaporator for leaks is to use the high-side float service valve. If you turn the valve stem to the left about five turns, the float needle — which is spring-loaded — if it is not stuck, will actually lift off from the orifice, thereby opening the high to the low side.
  • There is also a magnetic coil that fits over the high-side float and, when energized, it will lift the float and a needle away from the seat. Technicians used this coil to test the float in the field.
  • Since there always was a problem with the high-side float orifice getting clogged, it was routinely tested before evacuating and charging the unit. The dome was pressurized to 50 lb with dry nitrogen and the tube from the float to the evaporator was cut. If lifting the float by the service valve or the magnetic coil did not release any pressure, a thin pointed rod was then inserted into the tube to clear the clogged orifice. Repair the tube with silver solder.
  • You should use an old compressor with the discharge going outside the premises for the first air removal, and a deep vacuum pump for the final evacuation.
  • A final word of caution:I would sincerely advise against the restoration unless someone who has had experience with SO2 and monitor top can coach you.



    By John Lawler Nu-Calgon

    We’re writing in response to the answer provided to the question on burnouts in the Sept. 4News. The solution provided (CF-20) should not be considered the only alternative available.

    The question’s parameters of cost effective, safe for the system, environmentally safe, and non-hazardous to people, do not limit the answer to the one provided at the expense of other available solutions. And more importantly, the degree or severity of the burnout will also play a role in selecting a solution.

    Many equipment and component people will argue in different directions. Component folks will certainly suggest that multiple oil changes and drier changes comprise the best approach. And equipment people will have their preferred approach that will not include the solution proposed in the original answer.

    For that matter, we would certainly propose our own solution, Rx11-flush, as an attractive answer, given its degreasing capabilities, excellent evaporation rate and low boiling point.

    The point is that there are options and choices. Any such answer to handling a burnout should definitely urge the reader to identify the cause in the first place, and get it corrected.


    By Virginia KMP

    We happened to read in your Sept. 4 issue the question regarding burnout cleanup. The answer given by our good friend Dallas Rohrer was incorrect. In fact there are several products in the marketplace that will serve as compressor burnout clean- up. We at Virginia KMP have a new product that will serve that purpose. The product is named Opti-Flush. I would like to make sure that your readers are informed that CF 20 is not the only one in the market.

    New Refrigerants

    New RefrigerantsQUESTION:

    From C. Bernard Middletown, NY

    Where can I find the table(s) for the property of saturated liquids and saturated vapors for the new refrigerants?


    By Paul Reed DuPont Wilmington, DE

    Information on sources of saturated liquid and vapor properties for new refrigerants are available from refrigerant manufacturers for products of interest. For example, readers can contact DuPont in the United States at 800-234-7882; in Canada at 800-873-7882; or via the Internet at

    Valve Plate


    From Eric Hersbrook Eastpointe, MI

    I’m not clear on the procedure to inspect or replace a compressor valve plate. Here is my understanding of the process.

    1. Close the king valve at the receiver outlet.

    2. Jump the terminals or jimmy the low-pressure switch.

    3. Pump the low side down to pressure well into a vacuum.

    4. Close both the compressor service valves and vent the compressor discharge side into the low side.

    5. If the compressor pressure dropped below atmospheric, crack the king valve to allow the pressure to rise slightly above atmospheric before finally isolating the compressor for service.

    My misunderstanding lies in steps 4 and 5. In step 4, are the service valves front seated or back seated? I can’t see how the discharge side could vent back to the low side without the service valves being cracked or in mid-position. If they are front seated, the discharge line and suction line will be isolated from the compressor. If they are back seated, the gauge ports will be shut off.

    In Step 5, why wouldn’t the compressor pressure be left below atmospheric? You would still have to hook up a recovery machine to recover the refrigerant vapor, wouldn’t you?

    ANSWER: By Daniel Kramer, P.E. Patent Attorney and former Chief Engineer, Kramer-Trenton

    After pumping the low side into a vacuum, you should front seat only the compressor discharge service valve. Then you could vent the high pressure in the discharge side of the compressor head back into the low side through your gauge set. Keep a plug in the charging hose.

    If the pressure in the compressor was still in a vacuum, you could crack the king valve to get the pressure up to zero. Then you would front seat the suction service valve and remove the compressor head.

    Proper Cfm


    From Gregory Daw Poughkeepise, NY

    The basic guideline for determining the proper cfm of a blower unit in a forced hot air furnace, also used for air conditioning, is to use 400 cfm for each ton of cooling (12,000 Btu). How is this calculation affected by the height or vertical rise of the duct system when the blower is in the basement and cooling is required on the first floor, second floor, etc.?


    By Daniel Kramer, P.E. Patent Attorney and former Chief Engineer, Kramer-Trenton

    The relative elevation of the ducts in an air conditioning system should not affect the basic cfm requirement at all. However, long ducts with many elbows and braces might require you to employ a higher capacity blower to get a desired airflow.

    You would have to consult a duct chart and read from it the pressure drop per 100 equivalent ft of duct of your size with your desired airflow. The equivalent length of the various fittings and registers are available from charts and should be added to the actual duct length.

    Then, knowing the total pressure drop in inches water gauge that your duct with its fittings would impose, you could enter the chart for your blower to determine what you had to do to get the desired cfm.

    The Refrigeration Service Engineers Society Service Applications Manual Section 56 has substantially all the data you would need for this purpose. RSES can be reached at 847-297-6464; (website).

    Publication date: 12/04/2000