FAQ's and introduction to the CA.

The CA was introduced to make use of a newer, safer refrigerant. Two versions were made; the original 1933 form A, and the 1934 form B, which provided for extra non condensable gas storage.
Although the principles of operation are the same as other refrigerators, the operating conditions are not. Main differences are:

• Methyl formate (a liquid at atmospheric pressure) is used instead of sulphur dioxide or later “Freon” type refrigerants.
  

• The system works in a vacuum, except for the high side when under load.
  
• A rotary compressor is used.
  

• Unlike modern refrigerators, the evaporator is flooded, and a float valve is used as the metering device.
  

• A crankcase heater is required to prevent refrigerant condensing inside the compressor dome.
  

• Non condensable gases can be more prevalent than in other systems.
  

This leads to confusion when attempts are made to bring a CA unit into service; with the assumption the unit is faulty.
It is likely that one or more of the following will be evident with a newly acquired CA unit:

1. Trips overload/compressor is stalled/or makes rattling noise.

• Heater must be working and given 24hrs before machine is started. Check for approx 1000 ohms across the plug pins, or about
  

      12W power consumption, with the control in the “off” position. The heater runs continuously and there are no short cuts or bypasses for one which is faulty.

• There may be non condensable gas build up in the system.
  

• Most CA problems are due to either or both of these.
  

2. Low or erratic frost line.     

• Inoperative heater.
  

• Non condensable gas accumulation.
  

• Sticking float valve.
• Note that frost line will fluctuate slightly depending on loading. It should not fall below the bottom of the header tanks.
  

3. Hissing/rushing sound in float or evaporator.

• Float valve needle and seat worn or stuck open.
  

4. Poor cooling /long run time but correct frost line.

• Float valve needle and seat worn. Even if cabinet temperature can be maintained, compressor run time will be excessive.
  

• Door seal.
  

• Wet insulation.
  

Q: Can these troubles be repaired?
A:  Yes,

• Replacement heaters are available, or it is possible to make one using high power resistors.
  

• Non condensable gases can be purged from the system.
  

• Float valve faults can be eliminated with a capillary tube conversion, or if originality is important, by repairing the float valve seat.
  

• Modern seals and insulation are available.
  

Q: Can these refrigerators be recharged?
A:  Yes, methyl formate is available. Units have also been refilled with R11 (blackhorse, Iceman52) and R123 (jhigdon2). Other possible substitutes which have not been tried yet are R141b, R601a, and Carrene.
Methyl formate and substitutes are low pressure refrigerants, operating under or around atmospheric pressure. “Freon” types work at much higher pressures which
will overload, if not stall, the CA compressor.

Q: Isn’t methyl formate toxic?
A: No more so than other household solvents. In fact, G.E developed its use as a safer
alternative to sulphur dioxide. Methyl formate does not produce any unpleasant
odour. Only common sense precautions are required in handling it, as with other
solvents.

Q: Is the old wiring safe to use?
A:

• The mains cord should be replaced as a matter of course. Note that it is terminated in a locking connector – this requires a slight twist to remove it.
  

• The heater wiring should also be replaced as insulation failure could cause the fridge to become live at 120V. Its wires run against the copper tubing in the cabinet top.
  

• Compressor wiring should be replaced in the long term, although if not disturbed, complete failure is probably not likely.
  

Q: My CA seems to work fine. Is there anything that needs doing?
A:

• As above, wiring is likely to have failing insulation.
  

• Frost line should be checked to see it is half way up the left header tank, and at least to the lower part of the right header tank.
  

• Cycling times need to be checked; typically 3 to 5 mins run time, with 13 or more mins off, with cabinet temp of 32-38F.
  

      This needs to be checked with an empty cabinet, with the door kept closed,and the unit in operation for at least 12 hours.

• The cabinet insulation needs to be checked for moisture. This is easily done by removing the lower “Textolite” (black plastic) strip at the bottom of the door opening. If this is not checked and moisture is present, the cabinet will rust out from the inside, as well as cause poor performance. Gleaming paintwork on the outside gives no indication to internal condition.
  

• The cabinet top seals should be replaced to prevent moisture and condensation inside the cabinet walls and insulation. Any holes in the “No-ox-id” cloth, lining the top of the cabinet, must be repaired.
  

• The start relay contact should be visually examined for excessive pitting. Do not apply any pressure to the internal mechanism, or the sensitivity might be put out of adjustment, causing improper operation or motor burn out.

Q: How do I tell if there's Non Condensable Gases in my CA?

A:     Non condensables collect in the float chamber. Non condensable gases insulate the warm refrigerant from the walls of the float chamber, and thus the float chamber feels cooler to the touch, than the condenser.

• To test, measure the condenser temperature at both the top and bottom halves using an infra red thermometer. Then measure the float valve temperature. All three temperatures should be quite close. The machine must be running under load; e.g. place a tray of hot water in the evaporator.
  
• If the condenser gets cooler from top to bottom, and the float chamber is cooler still, indications are that NCG's are present.   
• Note that a stuck float valve can also cause the same symptom.

Examples: 1)Condenser measures 96F from top to bottom and float chamber measures 94F. The system does not need purging.

              2)Condenser measures 96F at top, 83F at bottom, and float chamber measures 81F. The system should be purged.