Post by cablehack on Aug 22, 2013 3:11:19 GMT
Because methyl formate is a liquid at atmospheric pressure and room temperature, the refilling procedure is very simple. Essentially, the liquid is poured into the charge valve without allowing air to enter. The following is the procedure I have used, but there are no doubt others - alternatives are welcome.
Items required:
As a further precaution against leakage, wrap a few turns of plastic tape around the charge valve/funnel connection.
Weighing in the Methyl Formate for float valve equipped CA's.
If not familiar with refrigeration scales, experiment with a container of water to see how the zeroing action works, and how the scales are used to show how the amount of liquid (in lbs) removed from the container can be shown. It is important to know what to expect when it comes to pouring in the methyl formate.
With the bottle of methyl formate on the scales, record the weight for future reference. Zero the scales. Now, as the bottle is emptied it is possible to see how much has gone into the cooling unit. For CA's with the original float valve, 2.75lbs is required for the CA-2, and 2.25lbs for the CA-1.
With the Bristol key inserted in the charge valve, decant some methyl formate into the funnel. Gradually open the valve and it will be sucked in by the vacuum.
As the methyl formate level approaches the top of the funnel nozzle, close the valve to prevent air entry.
Place the bottle back on the scales and record how much has gone in. Then repeat the process, until the required weight has entered the cooling unit.
For capillary converted CA's.
The procedure is the same as above, however less than the specified amount is required. It has to be found by experiment.
For each time the funnel is filled, run the compressor for a minute. This circulates the refrigerant rather than preventing a high load on the compressor if all the refrigerant is put in at once. The reason being, the capillary has small fixed orifice which could result in the liquid being sucked back to the high side of the compressor - this being the easiest path.
After about 50% of the specified charge has been put in, it is then necessary to fine tune the amount. It will be noted that even at half charge, the evaporator cools and a frost line appears. Progressively smaller amounts are then put in until the frost line is just above the bottom of the right side header tank. Note that several minutes of compressor run time are required for the frost line to settle at a particular level after starting.
Once the frost has reached this level, start recording cycling times after a day to allow stabilisation. Add very small amounts (such as .03 to .04lbs) while watching the cycling times. Again, it is necessary to wait a day or two to see the effects. Stop adding when cycling time starts to deteriorate.
If the conversion was done with the unit fully charged, it will be necessary to remove refrigerant instead.
The charge amount for a capillary converted unit is critical for best cycling times. It can only be found by experiment, but is roughly 90% of the original charge.
Things to note:
Items required:
- Bristol key: 6 flute, size .216.
- Medium size plastic funnel with nozzle end smaller than charge valve diameter.
- Methyl formate.
- Refrigeration scales.
As a further precaution against leakage, wrap a few turns of plastic tape around the charge valve/funnel connection.
Weighing in the Methyl Formate for float valve equipped CA's.
If not familiar with refrigeration scales, experiment with a container of water to see how the zeroing action works, and how the scales are used to show how the amount of liquid (in lbs) removed from the container can be shown. It is important to know what to expect when it comes to pouring in the methyl formate.
With the bottle of methyl formate on the scales, record the weight for future reference. Zero the scales. Now, as the bottle is emptied it is possible to see how much has gone into the cooling unit. For CA's with the original float valve, 2.75lbs is required for the CA-2, and 2.25lbs for the CA-1.
With the Bristol key inserted in the charge valve, decant some methyl formate into the funnel. Gradually open the valve and it will be sucked in by the vacuum.
As the methyl formate level approaches the top of the funnel nozzle, close the valve to prevent air entry.
Place the bottle back on the scales and record how much has gone in. Then repeat the process, until the required weight has entered the cooling unit.
For capillary converted CA's.
The procedure is the same as above, however less than the specified amount is required. It has to be found by experiment.
For each time the funnel is filled, run the compressor for a minute. This circulates the refrigerant rather than preventing a high load on the compressor if all the refrigerant is put in at once. The reason being, the capillary has small fixed orifice which could result in the liquid being sucked back to the high side of the compressor - this being the easiest path.
After about 50% of the specified charge has been put in, it is then necessary to fine tune the amount. It will be noted that even at half charge, the evaporator cools and a frost line appears. Progressively smaller amounts are then put in until the frost line is just above the bottom of the right side header tank. Note that several minutes of compressor run time are required for the frost line to settle at a particular level after starting.
Once the frost has reached this level, start recording cycling times after a day to allow stabilisation. Add very small amounts (such as .03 to .04lbs) while watching the cycling times. Again, it is necessary to wait a day or two to see the effects. Stop adding when cycling time starts to deteriorate.
If the conversion was done with the unit fully charged, it will be necessary to remove refrigerant instead.
The charge amount for a capillary converted unit is critical for best cycling times. It can only be found by experiment, but is roughly 90% of the original charge.
Things to note:
- For opening and closing the valve, it may be possible to use the Bristol wrench as supplied with the Hermetic Adaptor kit, depending on funnel size.
- Because of the flammable qualities of methyl formate, do this job away from any ignition sources as it has a low flash point temperature (e.g; a sparking switch).
- It is safe to refill indoors, but reasonable ventilation should be provided.
- The methyl formate bottles should be stored in a cool area (it boils at only 32C). Make sure the bottles are cool before opening them - they can be stored indefinitely in a refrigerator.
- As a rough guide to the amount required, methyl formate has a similar specific gravity to water. 1 litre of water weighs 1kg, which is about 2.2lbs.
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